What do these numbers tell you?

[coldbud]

Ok, HVAC professionals if I'm not out of line with my question here goes. My house size is 2300 sq.ft., two levels, the attic has 12 inches of cellulose, the walls are filled to R-11, the windows are double pane, LowE krypton filled with with a .28 U- factor and the entry doors are weatherstripped. The blower door test says the house has a .2 air changes per hour rating and the house is pretty tight. It also stated I need 55cfm in the house. Now, I have a Sears AC 2.5 or 3 ton unit that was installed in 1986 or 1987 and a Carrier 58SSB095-BC gas furnace that was installed in 1988. I would like to change both units out in order to receive better comfort and more efficency in my home. Ok , now for the hard part, my contractor say's his company does not normally do a load calculation on change outs and that should have been done when the original system was installed. Also if the current sizes worked fine cooling and heating the house stay with what I got except for modernizing the equipment. Based on his inspection of the property he thought a 3 ton 13 SEER unit and a 80% 2 stage VS system would work just fine based on his eyeballing the place. I realize most of you guys say "go with what your contractor recommends" but should that rule work in this situtation. The price of the equipment and install is not the problem, but am I getting the right size of equipment for the house. There are four people in the house and we like like it warm, not hot, in winter and cool in summer. We are in the mid-Atlantic section of the country. Sometimes cold and always hot in summer. Thank you for your input and have a cold one on me.

Rots-a- Ruck

[fat eddy]

Its really not that complicated if he is within a half ton either way it will be close enough, and he probably is. Load calcs in general are a waste of time and money, what if your load calc said a 39,000 BTU an hour ac system is needed. You would have to buy one higher or lower than that because if you go shopping for a 39,000BTU unit you won't have much luck finding one.

[BamaCracker]

Get a new contractor. If he did not do a load calc after you asked for one, he doesn't know how. That ios NOT a contractor you want to do business with.

Either that, or click the link on this page, download the software, and run your own.

I'd get a new contractor.

[dhvac]

trust your contractor? i dont want to so no for sure but i'de do some more checking. you can do your own heat load/loss calc by clicking the bullseye at the top of the page but we do them on every job for our customers. heck i thought they hired me cause i was the pro with the answers not just eyeballing and guessing. get a few more estimates.

[BamaCracker]

Originally posted by fat eddy
if you go shopping for a 39,000BTU unit you won't have much luck finding one.

Pretty easy to put together a system that produces 39,000 BtuH, just choose the airhandler and condenser from the manufacturer's extended ratings guide, or from the ARI website.

A load calc that is 1/2 ton off is no big deal, but I have seen contractors "eyeball" houses as much as three tons off on a 4 ton load. And my own house in Oklahoma was ONLY 1 ton oversized, but was uncomfortable as any house I ever lived in.

[joef]

I'm in the process of doing a replacemet A/C. My contractor had no problem with doing a load calculation. In fact, one of the reasons I chose the contractor that I did, was because he said he would do the calculation. I don't think my system was sized correctly when it was first installed, so the load calc was very important to me. I also got tired of hearing "if you like 3 tons, you'll love 4". It doesn't take much research to figure out that's exactly the wrong way to do it. Especially in the east (high humidity). All the posts from the pros on this board will tell you the key is to pick a good contractor. That's easier said than done. It actually takes some work to figure out the right questions to ask.

[rich pickering]

Heeeeeeeeeeeeeeeeeere's Bama

[fat eddy]

Do you feel that the existing size of your equipment was suffuceint for your home ? if so then so will the new one of the same size, any contractor that needs to do a load calc on such a standard type house probably doesn't have enough experience doing this kind of work. ( this actually applies to non standard houses as well) I would be embarassed if I needed to do a load calc to size a piece of residential equipment. gees o man c'mon U got to be kidding me this isn't rocket science no matter how hard you try to make it look like it.

[BamaCracker]

Originally posted by fat eddy
Do you feel that the existing size of your equipment was suffuceint for your home ? if so then so will the new one of the same size, any contractor that needs to do a load calc on such a standard type house probably doesn't have enough experience doing this kind of work. ( this actually applies to non standard houses as well) I would be embarassed if I needed to do a load calc to size a piece of residential equipment. gees o man c'mon U got to be kidding me this isn't rocket science no matter how hard you try to make it look like it.

If you refuse to do a load calc for a customer who wants one, you are a loser. If you think you can eyeball a load on every house, you're an idiot.

You might think what you do is not rocket science, but then you are doing it wrong.

I was a contractor and service tech for more than 15 years, and worked in the industry for more than 20, before becoming an engineer. And let me tell you this, it is closer to rocket science than even I thought it was.

Maybe you live in a part of the country where humidity is low and any size unit works good? Or maybe you live in a part of the world where people don't recognize comfort? Or maybe, just maybe, you are an idiot?

I don't know for sure, but I am willing to bet that one of those is correct.

[fat eddy]

None of those are correct, though I will agree that maybe everyone couldn't do what I do with the same amount of precision and accuracy (100%) but I know that I canand always do.

[BamaCracker]

Uh, huh.

Try this one:

1550 square feet in Norman, OK. 18 inches of wood cellulose in the attic, 5.5 inches in the walls. Double pane glass, on a slab, 3 bedroom, 2 bath.

Give it your best shot. Need more info? Just ask.

[condenseddave]

Wrong hill to die on, seriously.

A world of shit is headed your way if you continue on this kick.

[fat eddy]

And what temperature and relative humidity would you like to hold a 1% tolerance to sir ?

[condenseddave]

I can't look.

[fat eddy]

Now when I post the correct answer are you going to fess up or lie to make me look bad ?

[BamaCracker]

I would like to hold 72ºF, and . . . . .oh, let's make it easy on you. . .50% RH.

I have a family of four, two boys (13 and 10) and two large adults.

[condenseddave]

Bamacracker is a man of his word.

If you get it right, he'll admit it.

[berad]

Originally posted by fat eddy
Do you feel that the existing size of your equipment was suffuceint for your home ? if so then so will the new one of the same size, any contractor that needs to do a load calc on such a standard type house probably doesn't have enough experience doing this kind of work. ( this actually applies to non standard houses as well) I would be embarassed if I needed to do a load calc to size a piece of residential equipment. gees o man c'mon U got to be kidding me this isn't rocket science no matter how hard you try to make it look like it.

If for no other reason you should run a load calc and keep it in the customer file in case you get dragged to court. I've been surprised by equipment sizes from my load calcs occasionaly. I run those twice, they come up the same, I put them in and get good feedback. Every time a system is oversized you screw your customers' power bills.

[a\c don]

Originally posted by fat eddy
Do you feel that the existing size of your equipment was suffuceint for your home ? if so then so will the new one of the same size, any contractor that needs to do a load calc on such a standard type house probably doesn't have enough experience doing this kind of work. ( this actually applies to non standard houses as well) I would be embarassed if I needed to do a load calc to size a piece of residential equipment. gees o man c'mon U got to be kidding me this isn't rocket science no matter how hard you try to make it look like it.

WOW!

[BamaCracker]

Actually, most of the older guys here already know the answer, cause I posted it here about 4 years ago. I also posted it in other forums as well. In addition, I have photos, and the load calc I did before rebuilding the A/C to my own specs.