load calcs and duct work question

[lkstl]

I apologize because I forgot to add this on to my last question, but I've noticed all over the forum that it's almost a universal recommendation from you pro's to make sure my contractor does a load calculation and measures the duct work in my house to ensure they're selling me on the correct sized system.
I've had 4 of the more reputable companies out for bids and not one of them has done this.
Is it something I should have to ask them to do, or am I calling the wrong companies?
I have a basic 35 year old ranch in the midwest, and these guys typically just look at my old equipment to make their decisions on deciding what to offer me.
Can it be they've done it so long it's second nature and easy for them to tell?
This is the last heat and AC I hope to buy so I don't want to kick myself for the next 15 years because I made a mistake.

Thanks for any advice.

[Gunnery Sergeant Hartman]

ask them to and if they decline, then decline to have them bid your job...
They should do it without you asking, but who knows???

[Reliant Air]

They might have done it already and simply just not provided you with the report.

[dash]

If they did a calulation you'd likely have noticed the time spent measuring the home and windows ,plus checking the R value of the insulation.I doubt they did.

Now is you are in a subdivision they are very familar with,they may know fairly well that it's sized correctly.If it was sized tooo small,you would know and surely have told them.

If it's oversized,the danger is ,you don't realize it,and they didn't do a calculation.

When we do calcs and the home needs a half or one ton less,it's a battle to get the owner to downsize,but we at least put it in writing,to cover us.

Signs of being oversized:

System cycles on/off often on the coldest and or hottest days.

Damp feeling in the summer,bath towels take a long time to dry.

[heetseeker]

lkstl
I know exactly what you are talking about since I am going through the same thing. Nobody seems to to a real load calc. I am sure it is because most people don't ask. It takes time and they may not get the job. The most common method seems to be to look at the size of the old equipment. Others do an estimate on the square footage of the home. I even had one sales guy measure the room sizes and the windows but there were no questions about the insulation. My question is this: Does importance of the the load calculation decrease with a two stage or modulating furnace since it will run on low fire most of the time decreasing the short cycling seen with oversizing.

[dash]

Originally posted by heetseeker
lkstl
I know exactly what you are talking about since I am going through the same thing. Nobody seems to to a real load calc. I am sure it is because most people don't ask. It takes time and they may not get the job. The most common method seems to be to look at the size of the old equipment. Others do an estimate on the square footage of the home. I even had one sales guy measure the room sizes and the windows but there were no questions about the insulation. My question is this: Does importance of the the load calculation decrease with a two stage or modulating furnace since it will run on low fire most of the time decreasing the short cycling seen with oversizing.

Bingo,it certainly does.

So this fact will give the industry another resason to skip the load calculation.

To add to my last post,another problem is when we do a calc.,and the system should be smaller,the customer says the competition says,No you the same size or even larger.

Lots of consumer education needed in this area.

[tuccillo]

Originally posted by lkstl
I apologize because I forgot to add this on to my last question, but I've noticed all over the forum that it's almost a universal recommendation from you pro's to make sure my contractor does a load calculation and measures the duct work in my house to ensure they're selling me on the correct sized system.
I've had 4 of the more reputable companies out for bids and not one of them has done this.
Is it something I should have to ask them to do, or am I calling the wrong companies?
I have a basic 35 year old ranch in the midwest, and these guys typically just look at my old equipment to make their decisions on deciding what to offer me.
Can it be they've done it so long it's second nature and easy for them to tell?
This is the last heat and AC I hope to buy so I don't want to kick myself for the next 15 years because I made a mistake.

Thanks for any advice.

I recently asked for 4 bids for HVAC on a new house. Only one contractor actually did a Manual J. One said he did but when I asked to see his work he claimed he had deleted from his computer ( I really dont think he did one ). The other two didnt do Manual J calculations. We wound up going with the contractor that did the Manual J calculations. I have spoken with friends of mine who have received quotes for replacement systems without any indication of what equipment they were bidding.

[detroit_pierogi]

What do you guys think about trying to do our own load calculations, like with the free trial program that is advertised at the top of this site ?

[chrisc]

From a contractors point of view, a home with 35 year old duct work was originally designed to heat your home, cooling was a far off secondary back then. I would primarily focus on the duct sizes of your main supply ductwork, branch ducts and return duct sizing. If I felt those ducts were inadequate to cool the house, then I would make a point to upgrade the ducts to a size that would accommadate a properly sized system for your home. If the price makes your eyeballs pop out of their sockets the only other thing that can be done is to size the system according your blower size and/or main supply/return duct sizes. Additional supplys or returns may be neccessary to properly accommadate the new system. Your economic situation may overrule system efficiency in this particular situation.

[jdew1920]

Detroit - why don't you down load it and try to use it. You'll see that the trial version doesn't give you any info. You'll have to cough up a few bucks for a working copy.

[amickracing]

Originally posted by heetseeker
lkstlI even had one sales guy measure the room sizes and the windows but there were no questions about the insulation.

This isn't directed towards you, nor am I tryin to take the side of the person doing the calc but... I can understand why he wouldn't ask what kind of insulation you have in the walls. Most home owners barely know how big thier house is, much less facts on it's construction. And if this place has had several owners the info is likely not to be transfered on. So either he rips some drywall open to see for sure, or just does his best to estimate what's in there by the age of the house and thickness of the walls.

[robertee]

I don't think anyone in my area does anything but rule of thumb. Sq.ft.=xxton. I had 3 contractors to look at my project and the only thing asked was square footage. None of them even saw or knew the size of my old unit or the duct work size. For 1900 sq.ft. two of the installers sized a 3 1/2 ton heat pump the other one wanted to install a 3 ton.

[Jax]

If you read this board regularly you would think a load calculation was done on every furnace/AC replacement.
Truth is in the real world it is not done and it is not necessary.
Don, the man who wrote the advertised heat load program on this site is probably one of the most knowledgeable people on the subject.
In his response to a question about heat loads a few weeks ago he said at best a heat load is a good estimate. And anyone who understands loads knows he is dead on the mark.
It takes time to do a good load calculation and then you are guessing at the insulation in the walls, construction etc. No matter how accurate, several contractors will not come up with the same load. It is not an exact science. After you have load caculation, you need to take into consideration your usage and life style.
But you have a working system that can tell you far more than heat loads. You have Real world testing of a known sized system. You should convey to your contractor any short coming your system has. An experience contractor can size your system correctly without a load. I do it every day.
If you are replacing you duct system, then by all means do a load.
If there are serious problem, address them.
But to do a load calculation only to use the existing duct system makes little sense.

Jax

[AllTemp]

Originally posted by detroit_pierogi
What do you guys think about trying to do our own load calculations, like with the free trial program that is advertised at the top of this site ?

Hey, didn;t I advise you to do this days ago on anotehr thread?

GREAT IDEA!

Thats a pretty good offer if I say so myself. Download it and have some fun with it!

Lets us know how you did...

[framehvac]

Originally posted by AllTemp

Originally posted by detroit_pierogi
What do you guys think about trying to do our own load calculations, like with the free trial program that is advertised at the top of this site ?

Hey, didn;t I advise you to do this days ago on anotehr thread?

GREAT IDEA!

Thats a pretty good offer if I say so myself. Download it and have some fun with it!

Lets us know how you did...

Ok AllTemp your ad is just wrong in so many ways you should have to pay money for a ad like that.Why didn't I think of that?

[professor hvac]

There arte many things that can change over the years since the last time the heating and air have been replaced! If the insulation has settled or been added to, then the cooling load would be different. If there have been any updated windows, doors, or even the color of the roof!

Then again if you go by the equipment that is being replacesd, you are asumming that the last guy that installed the system did everything right and did a load calc on the house and did it right!!!

Many contractors don't like to run loads on every bid they give because it takes a lot of time and time is money! I usually told customers that the estamate was also an estamate on the size and it should be in the ball park and if they were interested in my estamate then I would run a load calc from that point!

I never would start a job without doing a load calc on it first!

[pstu]

>>But you have a working system that can tell you far more than heat loads. You have Real world testing of a known sized system.

Thank you Jax, for pointing out something very logical. I still have the highest respect for all the educated experts who advocate the ACCA calculations (Manual J, D, etc.), I think they have a lot to teach us. I do think another valid area of inquiry is how to get the most out of a system being *already* installed. For example all the measurements you can make which are not available prior to building, starting with the obvious "does it make you comfortable?". Of course measurements are less subjective and help any two people communicate better.

In the end, if we have a brain like Lstiburek and enough time to figure things out, I expect the ACCA methods to generally agree with after-the-fact real world testing. But at the present, I would need somebody to explain a lot of details.

Best wishes -- P.Student