View Full Version : Buying a furnance and AC unit
09-19-2005, 11:32 AM
I have a 2700 Square Foot home. Live around the Toronto area in Canada.
My wife has complained that our house (which 18 years old) was too cold so I have done the following
- I recently had the windows re-done
- 40 Bags of insulation blown into the actic.
- An actic electric fan (for the summer)
She is still cold.
So now it is time I put in an AC/Furnace.
I have been told that my 2.5 TON AC unit is working but it is too small. I was also told my 75K BTU is too small.
What is the recomend TONNAGE and BTU for a 2700 SQFT home.
The 2700 SQFT is based on two stories we do use the basement, so the actual living space including the basement would be about 4K SQFT..
09-19-2005, 11:45 AM
Get a Load Calc done (ret tab up top).
Till then, everything is just a guess!
09-19-2005, 12:01 PM
75k BTU furnace in Canada?....that's probably enough furnace for a mobile home!! Seriously, for a 4k sq ft house up there, at least double that (maybe even triple). Have a heat loss done to know what you really need though...especially since you have better windows now. Be sure the duct work can handle the furnace you'll soon install. The existing ducts may work for heating, but undersized ducts with cooling is a no-no. You running oil heat by chance?
09-19-2005, 01:26 PM
120,000 BTU furnace with a 4 Ton Condenser & TXV Coil.
Also put in a Zoning system for each floor.
09-19-2005, 02:26 PM
If the furnace keeps the house as warm as you want it during the winter, it can't be undersized.
If the A/C keeps the house as cool as you want it during the summer, it can't be undersized. [edit: Thanks dash, my brain is running faster than my fingers!]
Small is beautiful when it comes to energy efficiency, so if your small equipment is doing the job, don't rush to switch to larger equipment. Given all the insulation and window changes you've made this year, it would be best to actually do a load calculation before selecting new equipment. It could be that they were undersized before the energy improvements, but that they are just the right size now. It's hard to tell until you (or somebody) runs a load calculation.
You can buy a the homeowner version of the HVAC-Calc software and do your own calculations for $50. That's what I did when I had my mechanical systems redone last year. You may be able to find a contractor to do them, but many are unwilling to invest the time to do such detailed calculations (at least before the sale is made). Sizing by rules of thumb based on square footage, while common, is not the best choice for comfort or efficiency.
[Edited by wyounger on 09-19-2005 at 02:53 PM]
Originally posted by wyounger
If the A/C keeps the house as cool as you want it during the summer, it can't be oversized.
I'm sure you meant,"can't be undersized".
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