How to determine if my heating & cooling system is adequate for my home?

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Old 02-10-15, 08:16 AM
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Question How to determine if my heating & cooling system is adequate for my home?

Is there some kind of calculation I can follow to determine if the heating and cooling system in my home is rated (adequate) for the size of the house?

I assume there is some way to say something like “for X square feet per floor you need Y kind of system” for heating and cooling.

I recently bought a house (basement + 2 floors - ~1020 square feet per floor excluding garage) and I have the following system:
- Rheem heat-pump (Model - RPLB-030JAZ) which is rated as 30,000 BTU/HR (8.79 kW)
- Amana 15 kW Electric Furnace (Model – MBR1600AA-1AA)

So, trying to determine if this system is sufficient (or not)…
Thanks,
 
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Old 02-10-15, 08:24 AM
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You will need to do a heat load (manual J)
 
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Old 02-10-15, 08:40 AM
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Just off the top of my head I would say that might be a bit too large for a 2,000 square foot home in Canada. But Airman is correct, you really need to do a heat loss/gain calculation to be sure. Do a search using manual j heat loss/gain calculation as the search term for more information.
 
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Old 02-10-15, 09:20 AM
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But when we buy such a system, how do they determine what you need? I doubt the company will spend time and money on a barrage of tests - so how do they determine it? I had assumes it was simply based on the home square footage - at least for a good approximation.
 
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Old 02-10-15, 09:32 AM
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Any good company will do a Manual J. Doesn't take that long and it's a good indication of a quality company. It's not a bunch of tests, it's just some measurements and typing into a computer basically. Square footage is just a "rule of thumb" guess. And it's just a WAG. You really need to take all the design into consideration. Number of windows and doors, height of ceilings, actual cubic feet of the home (not just square footage), avg temps in your area, etc.

Too big and it will short cycle. Too small and it won't keep the set temps.
 
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Old 02-10-15, 09:59 AM
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I doubt the company will spend time and money on a barrage of tests - so how do they determine it?
Unfortunately, 4 out of 5 companies will likely just replace the unit with the same size you currently have.
 
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Old 02-11-15, 06:10 AM
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If you know that when the emergency heat is activated that the full 15kw is applied, then you can easily determine the heat loss as a function of temperature (load line) with a clock and a little patience.
1) turn thermostat to emHt, complete one cycle at normal room temperature, say 70F.
When the cycle ends, note the time (t1), note the ambient temperature, Ta .
2) wait until the thermostat activates the emHT, note the time, t2.
3) wait until heat cycles off, note the time, t3.

the amount of energy used for one heating cycle, from t1 to t3, is 15kw*(t3-t2) .
So you know the power consumption, p= 15kw*(t3-t2)/(t3-t1) to maintain the house temperature ... this is a point on the load line.
Another point on the load line is when 0 power is required, namely when the ambient temperature = room temperature.
Draw the load line, a straight line through (Ta,p) and (70,0).
Repeat a few times at different ambient conditions for improved accuracy, but even one cycle will probably answer your question.
 
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Old 02-11-15, 11:26 AM
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Try doing a load test of your house, this is a good calculator to give a ballpark.

Load-Calc
 
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