Heat Pumps and Electric Heating - Heat Loss/AC Load Calculation Question
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dcliptak
10-03-08, 11:59 AM
Hello- I've looked but have not seen a specific answer to this question- probably should have checked here first before proceeding...
Had a contractor out this morning to get an estimate to replace the heat pump portion of our 23 year old dual fuel HVAC system (gas furnace was replaced a few years ago by this same contractor). For our 2100 sq. ft house, they recommended a 15 or 16 SEER 3 ton unit. But they did not do a Load Calculation, and when I asked about it, the rep said he wasn't real familiar with doing the calculations, and it really was based "mostly on square footage". So I got no real answer on how they came up with these recommendations. First, is there some way I can do an estimate of this calculation myself? Should I request that they come back out and do the load calculation, given that he's "not really familiar" with it? Or should I get estimates from 2 other contractors with the load calculations to see if they are in line? The cost estimate seemed awfully high for our house, and I'm wondering now if I got the "Little Lady" treatment. Any insight would be welcome.
Had a contractor out this morning to get an estimate to replace the heat pump portion of our 23 year old dual fuel HVAC system (gas furnace was replaced a few years ago by this same contractor). For our 2100 sq. ft house, they recommended a 15 or 16 SEER 3 ton unit. But they did not do a Load Calculation, and when I asked about it, the rep said he wasn't real familiar with doing the calculations, and it really was based "mostly on square footage". So I got no real answer on how they came up with these recommendations. First, is there some way I can do an estimate of this calculation myself? Should I request that they come back out and do the load calculation, given that he's "not really familiar" with it? Or should I get estimates from 2 other contractors with the load calculations to see if they are in line? The cost estimate seemed awfully high for our house, and I'm wondering now if I got the "Little Lady" treatment. Any insight would be welcome.
Gunguy45
10-03-08, 12:24 PM
Run away, run away! If someone from a HVAC company doesn't know about Load Calcs, you don't need them working in your home either.
Call some other companies.
The Pro's will be in later, there are programs out there to do you own calculations if you know or can get the info they require.
Call some other companies.
The Pro's will be in later, there are programs out there to do you own calculations if you know or can get the info they require.
mattison
10-03-08, 01:48 PM
You can do it yourself using this one. http://hvaccomputer.com/talkref.asp
But as Gunguy said I would not use them if they do not practice load calcs. Anytime you get a new system you should get at least 3 quotes.
But as Gunguy said I would not use them if they do not practice load calcs. Anytime you get a new system you should get at least 3 quotes.
dcliptak
10-05-08, 09:34 AM
Thanks to both of you for the info- I'd have to find a PC in order to run this software- (using a mac now). I'll call some other contractors on Monday, and get estimates only from those who will do a load calc. I appreciate the help and advice.
Jarredsdad
10-05-08, 05:08 PM
Run away, run away!
Very funny, and very true.
You can also try Quickloads. Full funtioning for a number of program starts.
QuickLoads (http://www.obrienglobal.com/demos.htm)
Very funny, and very true.
You can also try Quickloads. Full funtioning for a number of program starts.
QuickLoads (http://www.obrienglobal.com/demos.htm)
dac122
10-07-08, 07:55 AM
Thanks to both of you for the info- I'd have to find a PC in order to run this software- (using a mac now). I'll call some other contractors on Monday, and get estimates only from those who will do a load calc. I appreciate the help and advice.
Yes, run, don't walk.
Get 3 (or more) quotes, ask for the load calc numbers, ask for various SEER/HSPF options from each contractor, and then repost the results here. Also post to hvac-talk as there are pros there that might point out some things such as a heat pump option that does not provide full heat btus compared to others.
You also want to be sure if they are mating to your existing air handler/fan you get the full HSPF rating. You don't want to pay for a 9.5 HSPF unit just to find out its really just an 8.2 because they didn't upgrade your air handler/fan
Realize the load calc (or Manual J as ACCA calls it) only tells you what tonnage you need via heat/cool btus. It will not tell you what SEER/HSPF you need. The higher SEER/HSPF numbers are a trade-off between upfront cost, operation cost and comfort.
Yes, run, don't walk.
Get 3 (or more) quotes, ask for the load calc numbers, ask for various SEER/HSPF options from each contractor, and then repost the results here. Also post to hvac-talk as there are pros there that might point out some things such as a heat pump option that does not provide full heat btus compared to others.
You also want to be sure if they are mating to your existing air handler/fan you get the full HSPF rating. You don't want to pay for a 9.5 HSPF unit just to find out its really just an 8.2 because they didn't upgrade your air handler/fan
Realize the load calc (or Manual J as ACCA calls it) only tells you what tonnage you need via heat/cool btus. It will not tell you what SEER/HSPF you need. The higher SEER/HSPF numbers are a trade-off between upfront cost, operation cost and comfort.