seeking replies from home owners..............

[Irishmist]

There seems to be a lot of discrepency within our own industry as to the importance of performing "load calculations" when a representative comes to your home.

I know many of you have come to this site to get advice and direction, and I am curious as to how many of you are aware of the importance of properly sizing your heating and air conditioning system, and more importantly the part that a properly performed load calculation plays in that process whether performed before, during, or after the proposal is made available to you.

The disagreement we seem to have on this subject has prompted me to get YOUR feedback. After all, your thoughts are the most important on the subject and I for one, would appreciate your candid reply.

Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is.

Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed.

And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.

Thank you.

Irishmist

[gary_g]

I think homeowners with older homes and/or original HVAC (probably oversized) equipment can benefit most from the Manual J. Also, homes that have insulation added, windows/doors upgraded, and storm doors added would also benefit greatly from not oversizing.

My case is a little different. Built on '86, all-electric, good Anderson windows, good insulation. Simply replaced the original 21 year-old 3-ton heat pump with another 3-ton heat pump. No Manual J done or needed in my opinion.

Take care.

[sprintmj19]

gary g...why would no Manual J be needed? Was one done when the house was built?

[safetyguy]

I have, in the past, bought a heat pump replacement without any type of load calculation. However, after being educated by the folks on this site, my next one (I hope its a a long time from now) will have a load calculation made to determine the correct size.

[gary_g]

gary g...why would no Manual J be needed? Was one done when the house was built?

I am the second owner so I don't know if a J was ever done.

I was satisfied with the way the old system performed so the new system was sized the same. I made no changes to the original insulation, windows, etc.

At 1800 square feet, I am probably oversized by a half ton. But in a climate that requires more heating than cooling, I need all the btu's from the heat pump I could get. The aux strips come on at low 20's ambient. I am happy with that.

Take care.

[gary_g]

I have, in the past, bought a heat pump replacement without any type of load calculation. However, after being educated by the folks on this site, my next one (I hope its a a long time from now) will have a load calculation made to determine the correct size.

You can do the load calc now, yourself.

HVAC-Calc at the top of the page. $50.

Take care.

[wahoo]

Here's a "new" task....run your manual J calculations, and then try and convince the homeowner that they will be "happier" with another size unit AFTER they tell you the old unit worked fine. Oh, by the way, the manual J shows they need a SMALLER AC unit, and they simply want the size they had. Been there, and most every contractor has. Remember, the customer may not be right, but they are still the customer, and the people "paying" the bill, so....if they aren't happy....????
P.S. Don't forget in our "push" to always do manual J, that very FEW customers operate their units within the parameters of the recommended manual J temperatures. Another point is that these new "Green" home recommendations will only allow the home to cool to @82 degrees on a 100 degree day (delta of 18). If the utilty company installs their "load control" thermostat, then the home won't even cool that well. Who will be responsible??? You guessed it, the contractor who sold them the new "comfort system"!!!
Gary also makes a good point with a slightly oversized heat pump!
I know the horse is already out of the corral, just thought I'd put in my 2 cents worth of things to think about!:anyone:

[ga-hvac-tech]

As usual, there is a balance somewhere in the middle... and where that middle is; changes with each customer.

Personally, I ask a bunch of question and LISTEN to the customer... then I know what they want... Some folks want a Man J and some folks do not...

Generally I will do it unless I see that it will cause more problems than it will solve.

[wahoo]

I agree ga-hvac, Do it (manual J), however "feel" the customer out. Following it to the letter may cause more problems than you want to deal with. Somewhere in the middle works for me!

[sancyk]

> "Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is."

My understanding of it is the total heat loss/gain through the entire building envelope. That would include heat gain from the sun and heat loss/gain through walls, windows, opening, etc via processes like conduction, infiltration, exfiltration, radiation....


> "Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed."

I think it's relatively important but is only of value if the person doing it knows what he's doing and looks at the big picture. I know they will look at window size and orientation but do they look at windows coverings and glass types ? For example, if I have honeycomb shades, awnings, or low-e glass the heat gain will change significantly. Do you take that in consideration ?

Let's face it, in an existing home, if your load calculation tells me that my ducts are undersized, chances are that I won't be in a position to do anything about it. So why bother doing the load calc ? If my existing 80% 90000 BTU furnace gives me enough comfort, why would I not be satisfied if you tell me that a new 95% 65000 BTU furnace will be good enough ?

Also, in a suburb where all the homes are identical, you do a load calc for one house and you probably have it done for most of them :-) If a contractor has done a lot of work in a particular neighbourhood, a load calc at each home may not be needed.

As a responsable homeowner, I don't want to waste your time more than I have to. I would be ok if you gave me a preliminary estimate based on your experience so that I can budget properly. Once I have it narrowed down to a contractor and/or equipment, then I would probably expect a load calc to finalise the size.



> "And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you."

See point number 2.

[Stamas]

I think homeowners with older homes and/or original HVAC (probably oversized) equipment can benefit most from the Manual J. Also, homes that have insulation added, windows/doors upgraded, and storm doors added would also benefit greatly from not oversizing.

My case is a little different. Built on '86, all-electric, good Anderson windows, good insulation. Simply replaced the original 21 year-old 3-ton heat pump with another 3-ton heat pump. No Manual J done or needed in my opinion.

Take care.

Just left a home that was same age. Had a 4-ton, replaced in 95 with a another 4-ton 2-stage. Gave a price on a 3 & 4 ton system on service call, but was contingent on load calc.
Came back-did calc and gave price on 3.5.
They were always comfy too.

[Carolinarider]

[Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is.
As I understand it, a load calculation determines the appropriate system size based on "standard" parameters for a given situation (i.e. location, insulation, people, size and number of external openings)

Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed.

Four months ago I would have suggested the it would be important only for new construction. Existing home owners would not benefit from it much because they alreay have a system installed and know what it provides in the way of comfort. Therefore they can provide that feedback to the installer and he could make an informed decision as to what needed to be done to improve the homeowners comfort.

I am now of the opinion that you a load caculation should be part of a good practice assocaited with every installation wether it be a new system on an new home or a replacement system. It should be done after the initial meeting with the homeowner before a specific system is suggested. Remember I am just a homeowner and not a HVAC professional. I have purchased two new systems in the last ten years and no one mentioned a load calculation. I would have been interested in having one done as well has having the ducts looked to determine appropriate size. No one every suggested.


And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.

Before, no. Now yes.

I am in the process of builiding a new home and am now looking for an HVAC contractor. I'll be sure that the one I select will do a Manual J calcualtion.

Although not a question asked, part of the problem implied in the question is understanding. You might be a cracker-jack installer with excellent quality but the home owner has little knowledge of the real workings of a system. The first task, it would seem to me, would be education. I'd much rather have someone installing my HVAC system that took the time to explain to me how the system affected by comfort, why it is necessary to do a load calculation (under sized or over sized units will have an effect on the comfort level) and then finally after all that is done and the home owner hads some understanding of what and how, provide the appropriate system to meet the needs identified.

It will take more time and maybe it's not something that can be done but I know in my case, if the guy who came out to my home to replace the HVAC unit had done that, I would feel alot better about the systems quality. Just because he took the time to educate me.

[gary_g]

Just left a home that was same age. Had a 4-ton, replaced in 95 with a another 4-ton 2-stage. Gave a price on a 3 & 4 ton system on service call, but was contingent on load calc.
Came back-did calc and gave price on 3.5.
They were always comfy too.

OK, so you dropped down a 1/2 ton.

If that were my house, I would not drop a 1/2 ton on a heat pump w/aux strips in Maryland.

Take care.

[mikethe ductman]

Just left a home that was same age. Had a 4-ton, replaced in 95 with a another 4-ton 2-stage. Gave a price on a 3 & 4 ton system on service call, but was contingent on load calc.
Came back-did calc and gave price on 3.5.
They were always comfy too.

That might work 9 out of 10 times, but what about the one guy that calls when its 110 degrees outside and he says his 4 ton worked better. Is 200 cfm's worth a couple trips back and a half dozen phone calls?

Here in Atlanta most units are undersized, when the building boom was going on the price to put in hvac was by the ton, if a builder could shave a ton off 100 or 500 homes well lets just say it ain't chump change.

[Irishmist]

Man it's like a friggin kindergarten around here. I solicit comments from homeowners on a relatively "hot" topic notwithstanding an important one, and there are nearly as many 'professional' replies as not.

Let the folks here in residential provide their opinions and comments WITHOUT any editorials from any of us; please.

Thanks.

Irish

[jerryd_2008]

Didn't build my house, 2nd owner. Built around '94 and had original system. Seemed tight and I added 6 " more of cellulose on top of badly disrupted fiberglass in attic. Pretty sure ducts were good if poorly designed. But increased 1 of 2 returns in size. Added some minor insulation under new siding on non-brick areas.

Had the local electric co-op do an economical blower door and infrared camera check along with a Manual J. Had a pretty good idea that the house was tight. Told all contractors they could NOT propose an AC capability larger than current. The old one was cooling fine. Asked for Manual J. Some did and some didn't. Finally allowed anyone to use the co-op calcs.

Got the exact same capacity HP in a DFHP replacing an old NG furnace and split AC. The new furnace was larger due to modularity. I think that a better review of the proposed equipment and house might have lead to a smaller furnace that would have been very adequate and even more comfortable and economical due to longer run times.

Totally agree that older homes are probably in the most need due to previous practices, DIY, rule-of-thumb, inefficient old equipment, etc.

[DavidPJ]

As a homeowner that has built several homes, I'm familiar with or at least know of load calculation and Manual J. I have always assumed, and probably incorrectly, that the builder would contract with someone that would perform the load calculation.

I feel the load calc should be done, and presented to the customer through their builder. The contractor can then temper the results with their experience. Sadly, I've never insisted on seeing a load calc and wish I would have in every case. My previous home's HVAC was terribly undersized and I later had the entire system zoned, which worked out great, but fairly expensive.

[Stamas]

Man it's like a friggin kindergarten around here. I solicit comments from homeowners on a relatively "hot" topic notwithstanding an important one, and there are nearly as many 'professional' replies as not.

Let the folks here in residential provide their opinions and comments WITHOUT any editorials from any of us; please.

Thanks.

Irish

Sorry,
I was watching this and was interested, but get some posting like they are pro's and know-but aren't and don't.
In voyeur mode now.See where it goes..............

[stevies3]

Hi,
I am the original owner of a condo built in 1987, Approx 2800 sq ft. located in Long Island, NY As mentioned in other posters the builder provided the same systems across the development, 2 zones for each home, Upstairs 1-2.5 ton (where all bedrooms are located) HP & 1-2.0 ton HP for the main level both with electric as backup.
I'm not aware that the builder or installer did any kind of manual J. But from talking to HVAC repairmen I have encountered over the years they felt it was properly sized.
Since first taking ownership we have replaced our windows & entry doors, added insullation to the attic floor & have had vinly sidding installed, Also about 8 years ago the local electric company offered to do an analysis of my home of which included a blower door test, sealing of all available duct work & cleaning of my coils on both systems. So now with these enhancements the home should now be better insullated than at purchase.
About 4 years ago we replaced both systems with Trane equipment, XL14 -2.5 ton HP with a VS air handler for the upstairs & XR13 - 2.5 ton HP with VS airhandler for the main level. We upped the tonnage for the main level as we finnished our basement & tapped into the first floors duct work to accomodate the basement heating & AC to reduce the cost of installing a 3rd zone. At no time was I told of a manual J or even knew about it. But the results are working well with no complaints. Would i have changed my tonnage based on the manual J, Thats a good question as proposed by several of you, I'm not sure, As a home owner with limited knowlege & changing what is the norm for the community.....
As Gary_G alluded to, Heat is more important to me than AC for my climate, I will guess I need AC for about 3-4 months & heat for about 6-7 months of the year.

[riderman]

Irishmist
I'll speak for a close neighbor. 2,000 sqft 2 story with a 3 ton HP. He needed a total system replacement. 4 bid's, 3 contractors performed J calculations. 2 bidders recomended replacing with same size 3 ton, two bidders, both who performed J calculations, recommended 2.5 ton but stated 3 ton would be OK. My neighbor was confused and asked my opinion. I know his wife likes it cold, about 71-72 degrees on those high humidity 95 degree day's we get a few times around here in Virginia Beach. Bottom line, he had the best contractor install a 2 stage 3 ton, VS AH with IAQ Tstat a couple of months ago. It's been cold here recently, his unit has been running mostly in second stage, but on the more moderate day's, it runs in first stage. He's been bragging to other neighbor's about his comfort. How would he feel with a 2.5 ton HP? I dont know. Do you think 2 stage units might be an answer to J calc's that are close between tonage and based on the customers specific heating\ cooling desires and not just a "green" J calc model?

[bwsaw]

We're about to replace a leaking Burnham Hydroponics oil fired cast iron boiler, and got quotes from our heating contractor/oil supplier for both steel and cast iron replacements. Manual J/load calc was not mentioned, but I will ask for one today before deciding. Seems very important to have, especially from an efficiency standpoint.

[erik337]

Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is.

Yes, I am aware of the term and have a clear understanding of it's meaning.


Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed.

I believe it is important for every residence to have properly sized HVAC equipment. I also believe the process and corresponding report should be standardized so that it is performed only when the building is new or significantly changed. I don't see the point of multiple calculations being performed on the same building.


And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.


It would make a difference, but would not necessarily be the determining factor for which contractor I chose. Hope this is helpful.

[Phasewolf]

My unit failed last year in the middle of January so I had little time to shop around. I feel lucky that I did do a load calc myself as no one else seem to want too and 2 of the contractors were way over sized on there guess. I went with the 3rd person and there guess is what the load really was. Sometimes home owners just don't have time too look around. It was important to me so I made sure I did it myself just in case.

[ILDAIP2]

28 year old house, 3000 sqft and going from natural gas to XP19 with G71. I had 5 quotes with the capacity ranging from 2-5T. No one did a load calc and only two of the five guys even bothered to review the number of hot air registers and the cold air return currently installed.

The two installers that did gave me some confidence that they were trying to work out what was a properly sized system. I three that didn't bother really didn't get a lot more consideration on that simple fact alone.

So with that experience in mind......


Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is.
After having reviewed the information on this side I now understand the concept of the load calculation and the importance of that guidance when working with a new install or an installation with enough changes to the assumptions about the building. (new insulation, additions/renovations, air sealing etc.)


Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed?
IMHO…. On the initial quotation to give the customer the peace of mind on the competence of the installer. I would place a large level of importance on this as even the simple task of counting registers did for my installation.


And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.
Without a doubt would make a difference even to the point of choosing a bid that is more expensive. I like the peace of mind.

As others have commented on, if the install is the simple replacement of existing equipment that has functioned properly then I don't think it would sway my judgment. Even if the load calculation shows an error in the original sizing at that point of the relationship the customer is trying to gain insight if they can trust the contractor. Tell them the equipment they have is flat wrong goes against the customers’ gut feeling that it has worked well. Could the correct sized equipment work better? Probably but that is a long road to educate a customer.

BTW: Tell the guys you work with and the installer not to mention when this is the first time you have ever done XYZ. (See my other thread on the G71 horizontal installation) You can loose all the trust made in the initial contacts.

IMHO

Dave

[Irishmist]

Thanks to all that replied. I sincerely appreciate your input since You are the reason for us being in business at all.

Again, thanks.

Irish

[hvacjonathan]

I am a homeowner and new to the industry professionally. I would definitely request that a heat load be done. It certainly isn't a make it or break it thing, but it will ultimately make the system more accurate and probably make it last a little longer. Any HVAC guy should be able to do one in about 30 min or less. Hope that helps!

[Gimmered]

I had my system changed out last spring and really didn't understand load calcs. I've been coming on here about everyday and learning constantly.

I'm likely oversized on my system but it is a 2 stage HP and a 2 stage 95% NG backup so that helps. I'll do a load calculation when I can spend $50 without my wife shooting me.

If I were starting over today I wouldn't consider replacing a system without one.

[kwilcox]

Well, my understanding is that a load calculation determines the most efficient system. Bigger is not better in HVAC because short cycling = lower efficiency/higher failure. The point here is that the "bigger is better" mentality must be a common assumption that causes difficulties and may even present resistance to costs etc associated with performing a proper load calculation as part of an HVAC install/upgrade.

[gary_g]

Well, my understanding is that a load calculation determines the most efficient system.

The load calc determines the size needed, not the efficiency.

Take care.

[jerryd_2008]

Well, my understanding is that a load calculation determines the most efficient system. Bigger is not better in HVAC because short cycling = lower efficiency/higher failure. The point here is that the "bigger is better" mentality must be a common assumption that causes difficulties and may even present resistance to costs etc associated with performing a proper load calculation as part of an HVAC install/upgrade.

But isn't putting in a little bigger system just a comfort and annoyance avoidance for many HVAC contractors? Isn't easy to explain to a HO that, yes it's hotter or colder than the design parameters, but 95%+ of the time it's much more efficient. A rationalization for overcoming HO lack of education, right?

[kwilcox]

That must be a bit of a treacherous path to walk for sure. I had my eyes opened here recently when one pro stated that a hvac system is at it's most efficient when it is running constantly to maintain the setpoint.

That turns so called "common sense" on its head since an uneducated person would think that a "bigger, badder" hvac system should be able to maintain a setpoint with a minimum amount of "work" and therefore be more efficient and last longer too because the parts are moving/burners burning less often.

A good friend of mine did that same thing in his cabin up north. Heat cycle lasts less than 5 minutes when I'm there in the dead of winter and he's wondering why his furnace ignitor needs replacing damn near annually while he's burning through propane like there's no tomorrow. Now I'm no pro but it seems to me that his furnace is oversized. Of course, nobody did a load calc.

[Jack2007]

There seems to be a lot of discrepency within our own industry as to the importance of performing "load calculations" when a representative comes to your home.

I went through the process of replacing my HVAC system in mid 2008 and in my area they don't like doing a load calc until an agreement is signed. They do an inspection of the house write down numbers and give their "estimate".


And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.

I would have liked to get a calc before signing an agreement but I understand the reluctance to "put in time" without a commitment. The three contractors all agreed on the size of the unit needed.

The contractor I decided on was highly recommended. I tried to get him to reduce the size from a four ton two stage heat pump to a three ton two stage but I'm glad he didn't budge.

The proper size would be 3 1/2 ton but two stage units did not come in half sizes. I have been very comfortable so far.

I should add that I spent a solid year reading here at HVAC Talk before getting contractors to do estimates. I'm glad I did.

.

[paul42]

Just a homeowner, but not a typical one. More like a typical engineer - or at least what I think a typical engineer should be like <grin>!

I did my own heat load calculations using HVAC Calc. I would have liked to see a confirmation from the contractor, but that didn't happen and I wasn't surprised.

I used HVAC Calc to help me figure out where to best spend my insulation dollars while building.

I used it to pick the size of the heat pump I needed for my house (2 tons for 4,000 sq. ft.)

I went out for bids on the installation and only one company was willing to bid on that small of a unit.

[gary_g]

I used it to pick the size of the heat pump I needed for my house (2 tons for 4,000 sq. ft.)

I went out for bids on the installation and only one company was willing to bid on that small of a unit.

Paul:

Don't you have a separate 3-ton mini-split for your master bedroom suite that you keep ice cold?

Is your bedroom suite included in that 4,000 sq-ft number?

Take care.

[paul42]

I have a 1.5 ton mini-split for the bedroom. We use it to cool the bedroom in the summer at night and heat the whole house in the winter.

In the summer, because the mini-split does such a horrible job of humidity control, I only run it at night. The 2 ton heat pump keeps the house at 74 degrees 40% humidity even on the hottest days I have seen so far - around 108.

In the winter, I run the mini-split 24 hours a day and it is enough to heat the whole house until the ambient goes below freezing. The coldest moring I have seen so far at my new house is 14 degrees, and the mini-split and heat pump were both running close to full time, but did not have to run the heat strips.

[jerryd_2008]

Just a homeowner, but not a typical one. More like a typical engineer - or at least what I think a typical engineer should be like <grin>!

I did my own heat load calculations using HVAC Calc. I would have liked to see a confirmation from the contractor, but that didn't happen and I wasn't surprised.

I used HVAC Calc to help me figure out where to best spend my insulation dollars while building.

I used it to pick the size of the heat pump I needed for my house (2 tons for 4,000 sq. ft.)

I went out for bids on the installation and only one company was willing to bid on that small of a unit.

Hope that is a mechanical engineer with HVAC experience. Technical background might make you more comfortable doing your own load calcs, but ....

I'm a HO, but tell me how a 2 ton HP can adequately handle a 4,000 sqft house. I want to do what you did!

The comment that only one contractor would go with that size seems to support my "nuisance avoidance" theory on contractor over sizing tendency.

[jerryd_2008]

28 year old house, 3000 sqft and going from natural gas to XP19 with G71. I had 5 quotes with the capacity ranging from 2-5T. No one did a load calc and only two of the five guys even bothered to review the number of hot air registers and the cold air return currently installed.



Dave, I checked your other thread but I didn't see the size that you finally installed. May have missed it but I'm curious as to how you got to what you picked when you had proposals in the 2-5 ton range!

What did you have previously? If it did a decent job, did you at least tell the contractors to not to exceed the current system?

[troutfly]

The load calc determines the size needed, not the efficiency.

Take care.

True,not the eff. of the equipment,but i know it has a lot to do with the eff. of the system.I offer a LC on every job,but i now have a new policy after reading a few of the posts.I will produce one when the proposal is signed,i'm tired of doing them for the HO to price me and jacka-- who call themselves pros.......

[troutfly]

[
I'm a HO, but tell me how a 2 ton HP can adequately handle a 4,000 sqft house. I want to do what you did!

.[/QUOTE]

His home is in the ground or he has superior r values.I have been around a few of these jobs......

[paul42]

Hope that is a mechanical engineer with HVAC experience. Technical background might make you more comfortable doing your own load calcs, but ....

I'm a HO, but tell me how a 2 ton HP can adequately handle a 4,000 sqft house. I want to do what you did!

The comment that only one contractor would go with that size seems to support my nuisance avoidance" theory on contractor over sizing tendency.

Nope, I'm an electrical engineer in the aerospace industry.

A load calc is not rocket science, especially when you have direct control over the design of the house and how it is insulated. HVAC-Calc is designed to be fairly easy to use.

To minimize the required A/C size
1. put the air handler and all duct work in conditioned space.
2. shade all the windows in the summer.
3. make the house air tight
4. adequate insulation

Engineering comes into play when trying to figure out the most cost effective means to do all of the above.

The house is 100% above ground.

I have R13 walls and R49 attic insulation. According to HVAC Calc, I went over board on the attic insulation - but cellulose was really cheap.

[jerryd_2008]

Nope, I'm an electrical engineer in the aerospace industry.

A load calc is not rocket science, especially when you have direct control over the design of the house and how it is insulated. HVAC-Calc is designed to be fairly easy to use.

To minimize the required A/C size
1. put the air handler and all duct work in conditioned space.
2. shade all the windows in the summer.
3. make the house air tight
4. adequate insulation

Engineering comes into play when trying to figure out the most cost effective means to do all of the above.

The house is 100% above ground.

I have R13 walls and R49 attic insulation. According to HVAC Calc, I went over board on the attic insulation - but cellulose was really cheap.

Got an excellent energy consultant/architect around here that work's with the electric co-ops that has a $40 video that tells me those things for new construction and as best you can in retrofit situations. And he has been advocating cellulose for 20 years. He says foam is great too but it's several times more expensive.

Paul, I'm not picking on you, but I still don't understand how 2 tons and a bit more insulation does it for that size house in Dallas, right? You must have done some serious house envelope work, including windows, doors, house orientation, etc.

[paul42]

Got an excellent energy consultant/architect around here that work's with the electric co-ops that has a $40 video that tells me those things for new construction and as best you can in retrofit situations. And he has been advocating cellulose for 20 years. He says foam is great too but it's several times more expensive.

Paul, I'm not picking on you, but I still don't understand how 2 tons and a bit more insulation does it for that size house in Dallas, right? You must have done some serious house envelope work, including windows, doors, house orientation, etc.

The windows & doors are not as much of an issue as you might think. I went with casement and fixed windows to cut down on infiltration, but they are standard vinyl windows. There are five doors, a mixture of metal cladd, wood, and fiberglass. The total heat gain through the doors & windows is less than 3,500 btu/h.

Orientation is important. My house is a big rectangle running pretty close to due east / west. The garage shades the east end of the house, and we designed the layout so that the only windows on the west end are some small windows right under the eves in the master bathroom. The sun hits them about 6pm in the summer - and I paid for extra low e-coatings on those.

The rest of the windows are shaded by a 3 foot overhang all around the house. My wife likes lots of light, so we have a lot of windows. But, they are right under the eve and even at 5 feet high, they are still well shaded.

I put a lot of thought & effort into air sealing the house. instead of a conventional house wrap, I used a peel & stick roofing membrane. It makes the walls both air & water tight. The walls are insulated with 4x8 sheets of 2 inch thick polyiso foam on the outside of the house wrap. It was more expensive than using cellulose, but a LOT cheaper than spray foam and totally eliminated bridging through the studs. It also eliminated possible problems with condensation etc.. Everything outside of the peel & stick roofing membrane is not affected by moisture. Everything inside the membrane stays at room temperature & humidity.

I put a lot of personal effort into making the ceiling air tight. Now, a better answer would be to have the insulation company spray in an inch of foam to the attic floor before blowing in the cellulose.

[jerryd_2008]

...

I put a lot of personal effort into making the ceiling air tight. Now, a better answer would be to have the insulation company spray in an inch of foam to the attic floor before blowing in the cellulose.

Went to an open house with an all-electric air-source HP. They did a lot of foam under cellulose. The energy consultant was there and thought that this was a bit of overkill compared to straight cellulose. Couldn't find my post on that, but I recall that this ~2800 sqft house had a sub-$100/month bill. Also used a separate small (1 ton?) HP for a media room in upstairs. Don't think they got away with 2 tons total though. I was really impressed with how quiet the Rheem inside blower was.

[newwindblowing]

Irish, you pose a most interesting question. am a ho monitoring this forum in anticipation of replacing original 20 yr old ng central air system installed in 1989. now am aware of hvac load calc. have 8 different proposals and not a mention of load calc from any. for me, diy calc seems ill conceived. public utilities do not offer. iho, fee for service load calc with dual fuel hybrid incremental cost pay back chart would go a long way to assist prospective clients. how does a ho relate to replacing a 140k btu (probably 0versized) with current equipment. if 3.5 ton ac not fully comfortable for 20 yrs why downsize? if furnaces jump sizes by 20k btu increments, what is load calc all about on a retro? i'd rather be attempting to buy a used car from sam sausage motors. Great Forum in any event--thanx all.

[needhelp7]

There seems to be a lot of discrepency within our own industry as to the importance of performing "load calculations" when a representative comes to your home.

I know many of you have come to this site to get advice and direction, and I am curious as to how many of you are aware of the importance of properly sizing your heating and air conditioning system, and more importantly the part that a properly performed load calculation plays in that process whether performed before, during, or after the proposal is made available to you.

The disagreement we seem to have on this subject has prompted me to get YOUR feedback. After all, your thoughts are the most important on the subject and I for one, would appreciate your candid reply.

Let me know if you are aware of the term "load calculation or heat loss/heat gain" and what your understanding of it is.

Secondly, could you let me know the level of importance that YOU apply to this task and where during the process you believe it should be performed.

And finally, let me know if it would make any difference to you whether a contractor performed a load calculation or not in the process of making their recommendations to you.

Thank you.

Irishmist

Just finished getting information via different thread for choosing an hvac contractor. Based on recommendations from these website discussions,we screened potential contractors with the simple question: "How do you size your units." Before we learned to do that, though, the contractors who came out didn't offer to run one, and based unit sizing on current unit - just added a ton to our what they thought was the current unit to accomodate our closing in our garage. Because of tightening up the house a bit, the fact our cureent 3.5T unit is oversized for existing area, and the better efficiency of today's units, they would have oversized us by 1-1/2T - priced 5T units, and we only need 3.5T (and some on this list think we could go even smaller) per manual J. That question weeded out 7 of 11 contractors, and the one we ended up with will guarantee we are satisfied.

The contractor we went with was the only one to do a Manual J before he gave us a quote - he might have done Manual N as well - and that is how he quotes ALL his jobs. Our elec co. ran one for us as well, but strongly suggested that whoever did our job do his own, to confirm the numbers. How could a contractor even make a proposal without load calc, if he is going to use load calc at all?

Thinking load calcs are VERY important in choosing a system that will provide comfort, and not just "well, it's blowing cold/hot air so it's working".

[ILDAIP2]

Dave, I checked your other thread but I didn't see the size that you finally installed. May have missed it but I'm curious as to how you got to what you picked when you had proposals in the 2-5 ton range!

What did you have previously? If it did a decent job, did you at least tell the contractors to not to exceed the current system?

Had a old NG furnance I was replacing so no rule of thumb to assist with the sizing. Ended up with a 3T. So far works fine with heating the structure but the noise (line set and return air) is way higher than expected. Installer just said that the only silent heat is radiant so get used to it. hum..... not quite what I wanted to hear.

IMHO in the area Vancouver we don't have qualified installers. At least none of the 5 I talked to could (I mean would) perform a load calc. They figured they could size it just using a rule of thumb..... 1T per 1000 sqft.

It's also typical to set the balance point at 34-35 degrees despite the efficency of the outdoor unit still being better than NG.

Dave

[pstu]

I am way late in responding to this thread, but I do believe a Manual J is only one way to get good sizing information. No argument that Manual J is the best method for new construction, and for when the person has not lived in the house. My point is that a homeowner has experience information not available to a visiting pro.

Grudgingly, I can see the merit in sizing by what was experienced to work before. Yes there are times when the old system did not do its job well, but not always.

I wish professionals would pay more attention to ductwork leakage and/or airflow issues, if we had to pick just one topic to focus on.

Thank you for asking -- Pstu

[gstein]

Speaking as someone who has spent an ungodly amount of money on HVAC issues and been burned nearly 100% of the time, I think an honest manual J is fine and dandy, but system size requirement is as much a function of duct design, installation quality, and similar factors as it is a function of heat load. For example, our current residence is 4200 SF with 10 tons of AC in Houston, which was supposedly determined with a Man J. Definitely oversized, but the ductwork is restrictive and unbalanced, 80% of air flow passes through only one side of each A coil, duct insulation is poor, etc. We need the full 10 tons to cool the house, dehumidification is poor, and our electric bills are painful. I suspect 5 or 6 tons would be more than adequate with a better install. Another example, our previous home in Florida was 3200SF with a 4 ton A/C. Properly sized according to Man J, maybe, but the ductwork is restrictive and runs at very high static pressures and can't be balanced making one side of the house 3 or 4 degrees warmer than the other. The A/C can't keep up on hot days. Our fancy 19 seer system gave us $350+ cooling bills (not including other electrical usage) in the summer.

I am not in the HVAC business, but it is obvious to me that sizing a system depends on much more than simple heat load. The problem I see is that Manual J calculations and, for that matter, manual D designs, are based on overly-simplified assumptions. Whether one is dealing with Global Warming, Nuclear Physics or a heat load calculation, a mathematical model is NOT reality. It is a useful tool that provides information, like a gage set, but it is simply a guess based upon certain incomplete assumptions. The results of a heat load calc might be useful or might be less-than-worthless BS, depending on the assumptions and how the results are interpreted. For example, we are currently renovating a house in Florida which the initial Man J calculation specified 5 tons of cooling. The original A/C was 4 tons, which was able to keep the house cool and mostly dehumidified on a hot day with single pane windows AFTER all of the insulation and sheetrock had been removed. The remodeled house will be very tight and super insulated. I don't believe it, 3 or 3.5 would likely be more than adequate. The Man J doesn't take into account the shading effect of the garage roof, roof pitch and convection, how many windows simultaneously face the sun, and tons of other variables. Of course, an inflexible county code enforcement department is involved so common sense does not apply.

Our contractor has a good reputation so I am sure we will be able to negotiate a workable design, but my point is that I think common sense and experience are far more important than the results of a calculation. I think the difference between a pro and a hack is a thorough understanding of his tools and their limitations.

Peace

[beenthere]

Speaking as someone who has spent an ungodly amount of money on HVAC issues and been burned nearly 100% of the time, I think an honest manual J is fine and dandy, but system size requirement is as much a function of duct design, installation quality, and similar factors as it is a function of heat load.

Manual J can't account for a bad install. That is not its purpose.