Heating & Cooling Calculations & Equipment

corgi11

Could somebody please explain to me equipment & calculations. Most of the central air conditioners in my area are 24k to 36k. If I accidently do the calculations wrong and pick a 30k instead of a 24k unit I am basically one bedroom unit to large and that difference is spread over the entire house. My new boiler is 10k smaller gross than my old one. That is about 2 electric portable heaters spread over my house also. My question is if you are close on the the heat gain or loss even if you are 5 or 10k under on the heating and have to go up 40k are you better being 5 or 10k under or should you go up to the next size. It seems to me central air at 6k difference per unit is not as critical.

Thank You guys for always helping.

EdTheHeaterMan

It's not Rocket Surgery. getting as close as you can without being too small if the goal. When it comes to undersizing you won't know about it until it is at the "Design Temperature". if you are too small. On a heater if it was designed for a low temperature of 10°F to be 70°F inside and you need a 52000 BTU NET output. and you chose a 42,000 BTU NET output then it will work just fine at an outside temperature of 25° or even 20°. The trouble starts when a 42000 can only get you a 50° higher temperature inside than the outside temperature. So when it gets to 19° outside you will only be able to get 69° inside. Likewise when it gets to 15° outside then the inside temperature will get to 65° and that is all that you will get. The burner can't make any more heat than the amount of fuel that can go into it. So your decision to use the smaller because the larger was "in your opinion" is Too large… then you will need do deal with that problem when it gets cold outside.

By the way, when it is really cold outside there will be nothing you can do about it but that service call will be there to waste your time when you could be out there making money on other service calls fixing frozen pipes.

corgi11

Thank You

pecmsg

On the A/C side I advise Smaller is better. An Oversized system will never be proper 100% of the time, an undersized system will be only wrong maybe 1 or 2% of the time.

corgi11

Thank You