Ton to Square Foot rule of thumb?

[Mr Bill]

If people learned how to use manual J and Manual S like they are suppose to. they wouldn't have to worry about how small the manual j load is.

I even go a step farther, I personally think any LC's period/home energy audits, should become a trade withing itself. Most of of old guys started out running service and installations that was enough, now like me most of us older folks are probably just running service and have install crews. I don't know about the larger companies, maybe they have folks on the payrolls that can do all this sealing the envelope stuff, but I need all my help I have on the front lines, not performing LC's. I personally believe it would benefit the whole trade to take the responsibility and liability off the backs of the a/c and heating service companies, then we could concentrate on our job we were born into to perform, not doing something we had forced upon us. This would be so easy, Mr. Jones we would love to set you up with a new system, let me give you the number of a professionally "qualified" company that can perform an LC and energy audit on your home and when there finished we can fix you up, takes the liability of sizing correctly off our backs. Let me tell you, I would rather have my wisdom teeth pulled, than go through the anguish of wondering if the system we installed in "Houston" if going to be the correct size according to the LC performed, do we really need this added burden on us? I have enough on my plate just keeping up with my everyday calls.

[54regcab]

Ah...
they taught us manual J, D, and P, but id never seen S until now,
very interesting

http://www.constructionbook.com/acca...cca-standards/

"Why the "400 CFM per ton rule" is a myth, why the blower CFM is exclusively defined by the sensible heat equation, why lower DX coil air flow rates are compatible with humid climates, and why water source refrigeration cycle equipment should not be sized to satisfy the design heating load"

I too believe the 400 CFM/ton is a myth. In an ideal world the thermostat should be able to control the CFM/tom based on sensible vs latent load. If the humidity is high slow the blower down to the point where the maximum humidity is removed regardless of sensible capacity. If humidity is low put the blower on the speed that offers the highest sensible capacity per watt. There's no reason systems today can't do that since they make thermostats can sense humidity and equipment that can communicate. If this means a Low CFM of 250/ton and a high CFM of 600/ton so be it... IMHO this would reduce real world power use while maintaining comfort.

[tedkidd]

Kidd,


When you get to close to talking about System Efficiencies, Sealing/Insulating, and the dynamics of looking at the house as a whole, you start to hit the nerves of the "swap the AC" and the "customer can't afford it" gang.

If you take a poll of the past 10 ACCA presidents you will find all of these companies now focus on the house as a whole.

As you are also aware, AC contractors are losing lots of work due to not moving in this direction. They loose lots of work, but they don't see that. You don't see the jobs you lose to other companies and trades where you were never even invited to participate.

The nice juicy fish are increasingly being caught upstream from them. Then they will tell you about all they see are price shopper fish, parts swapper fish, fish with no credit, etc.. No Sht. The good ons were caught upstream.

ACBD

Homer Simpson "doh" moment. Separating fix it right and fix it cheap homeowners. They see the fix it cheap folks. The only non-communicating equipment I've ever sold has been due to fact none are rated for mobile homes. It's a mindset. Helpful, thanks.

MR BILL - you nailed it!! That's EXACTLY what I'm trying to build! Bring design build to resi, or at least the spec part of bid spec. Take it a step further, it's on US (meaning Auditors) to learn what idiot behaviors people think are "smart", and train homeowners how to properly operate their equipment, manage comfort, and what expectations are reasonable. It's the auditors job to teach building science and efficient operation, further freeing you to focus on getting your part right.

[Mr Bill]

H.The only non-communicating equipment I've ever sold has been due to fact none are rated for mobile homes. It's a mindset. Helpful, thanks.

Technically even the old stuff communicated, the stat told the AH/Furnace and condenser when to come on.

[udarrell]

Homer Simpson "doh" moment. Separating fix it right and fix it cheap homeowners. They see the fix it cheap folks. The only non-communicating equipment I've ever sold has been due to fact none are rated for mobile homes. It's a mindset. Helpful, thanks.

MR BILL - you nailed it!! That's EXACTLY what I'm trying to build! Bring design build to resi, or at least the spec part of bid spec.

Take it a step further, it's on US (meaning Auditors) to learn what idiot behaviors people think are "smart", and train homeowners how to properly operate their equipment, manage comfort, and what expectations are reasonable. It's the auditors job to teach building science and efficient operation, further freeing you to focus on getting your part right.

Well, from the headache & liability aspect, I tend to agree with Mr. Bill & tedkidd but some contractors could have a unit doing half what it should & they will simple tell the person they should have put in a larger tonnage or, without any real test data they'll say it's doing all it can...

The reason I once said that contractors need to get involved in Home Audits, is because there are not enough Raters or Auditors to cover the need.

Yes, for numerous reasons, both Home Auditing & Load Calc's (LC's) really ought to be performed by experts, with all the required test instruments & software, along with actual equipment sizing, - separate from the contractor.

That would sure take a lot of weight off overloaded HVAC/R Contractors.

This is really strange, in all the years I did equipment replacements & fixing poor performing systems, I never had one complaint that it wasn't cooling well enough for them; I still can't believe it. Maybe they just called someone else?

A lot of the equipment was oversized with many aspects of the duct system too small & screwed-up. Back in the 1970's when electric power was relatively cheap, a lot of us ignored too much, including me...

Well; this is a new energy era, however, customers & too many contractors haven't caught-up.

[thes]

Well, from the headache & liability aspect, I tend to agree with Mr. Bill & tedkidd but some contractors could have a unit doing half what it should & they will simple tell the person they should have put in a larger tonnage or, without any real test data they'll say it's doing all it can...

The reason I once said that contractors need to get involved in Home Audits, is because there are not enough Raters or Auditors to cover the need.

Yes, for numerous reasons, both Home Auditing & Load Calc's (LC's) really ought to be performed by experts, with all the required test instruments & software, along with actual equipment sizing, - separate from the contractor.

That would sure take a lot of weight off overloaded HVAC/R Contractors.

This is really strange, in all the years I did equipment replacements & fixing poor performing systems, I never had one complaint that it wasn't cooling well enough for them; I still can't believe it. Maybe they just called someone else?

A lot of the equipment was oversized with many aspects of the duct system too small & screwed-up. Back in the 1970's when electric power was relatively cheap, a lot of us ignored too much, including me...

Well; this is a new energy era, however, customers & too many contractors haven't caught-up.

hey brother here's the deal, basically this will start with new construction, where the codes say load calcs etc. there are a lot of architects,who don't know load calc nor do they care! the problem IMHO, is simple,loading out,and designing a hvac system is a separate trade/profession. to think most,not all ,but most hvac co. are going to be proficient in every aspect of this trade. ain't happening, there's too much too know, ain't happening, especially on basici residentil hvac.i was at a field controls seminar one time and the instuctor tom, was saying you guys should expand into IAQ. i told him that should be a separate trade. as long as this industry thinks one guy is going to know IAQ,load calc, humidification,design/layout,control wiring of complicated units,etc, they will be dissapointed. there is a reason dr.s specialize,lawyers specialize,accountants specialize,i know plumbers that specialize in just installs, others repair and replacement. IMHO, this trade was set up as mom/pop operations putting in basic systems, with all the new products being intro'd into the market at break necking speed, a total rethought of the way this trade is approached is in order, but IMHO what it always get down to is real simple 80% of the h/o's it gets down to one thing$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$. i think that out in calif. they have new rules on new const. like blower door tests and so forth.
i agree we're approaching a new era, but change is usally slow, but guys should be aware it's coming.

[Mr Bill]

This is really strange, in all the years I did equipment replacements & fixing poor performing systems, I never had one complaint that it wasn't cooling well enough for them; I still can't believe it. Maybe they just called someone else?

Hey Darrell this is what I am thinking also, since 1978 no call backs on new systems not performing as expected, maybe all my customers have low expectations.

[thes]

i'll just throw this out there, they should have a code, what ever , that it's up to a homeowner to get a load calc, before installing a hvac system or up grading! this way a contractor approaching the job, is given the load sheet by johnny h/o and every one knows what's going on. they can have co's that specialize in this,the way this trade is set up, you can actually have 10 contractors bid on a job and have 10 guys give 10 load calcs. that's stupid,inefficient,wastes everyone's time. the reason it won't happen is the h/o wants free estimates,free load calcs,free what ever. again the way this whole hvac industry is set up, especially on the residential side, is F@#%$D up. you basically have a bunch of mom and pop operators that where set up for basic systems, and you add the builders who will beat you up with a crow bar, to get the price below cost. it ='s bad results! again change is slow, but IS coming!

[Mr Bill]

you can actually have 10 contractors bid on a job and have 10 guys give 10 load calcs. that's stupid,inefficient,wastes everyone's time. the reason it won't happen is the h/o wants free estimates,free load calcs,free what ever.

And, if they had to "PAY" for the load calcs that would stop a lot of tire kickers, not all but a lot.

[thes]

And, if they had to "PAY" for the load calcs that would stop a lot of tire kickers, not all but a lot.

AGEED-AGREED-AGREED=AGREED- i was in a stationary store a while back, and they had a indian guy roaming around and asked me if i can help you, i told him i'm just kicking tires, his response "was what's kicking tires" ?
change is coming!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
the saying kicking tires is going the way of the edsel!

[54regcab]

Perhaps make the building code set a maximum size that can be installed per sqft based on age of home and area. This would force contractors to fix the cooling/heating load rather than just installing bigger equipment.

[Mr Bill]

the saying kicking tires is going the way of the edsel!

How about coming into the 70's "Hey Dude it would be groovy if you could slide by, I am looking at prices for a new system" I am @ 714 Haight Ashbury, even if I don't buy we could still drop some acid.

[thes]

Perhaps make the building code set a maximum size that can be installed per sqft based on age of home and area. This would force contractors to fix the cooling/heating load rather than just installing bigger equipment.

for guys in the trade i hear ya, but again, just like the dry r-22 units the epa let them do it, because johnny h/o just might not have the money, people get p@@@@d when the government comes in and start to tell you that you have to do that! it gets down to $$$$$$$$$$$$$$$ jmho.
imho we are gravitating toward energy efficiency,building upgrades on older homes but it's a process, slow but progrssing. anyone in the trade or just getting in should just be aware its coming! and to stay on top of the changes in there area!