View Full Version : Size of HeatPump
11-15-2005, 09:19 AM
In our upstairs, we have 960 sq ft consisting of 4bed 2 baths. We will have 1 heat pump to service this area. My contractor is pushing me to get:
* 3 Ton variable speed air handler
* 2.5 Ton Heat pump
Isn't that to big? What are the advantages & disadvantages to putting in an oversized unit? Will I be blown out by rushing air when the system is on? Will I spend more $ on electric costs?
11-15-2005, 10:33 AM
Only a load calc will tell you if it is too big. Sounds like it to me but depends upon location, windows, insulation, etc. Before putting 2.5 tons on that small of a space, demand to see how he arrived at that calculation and get assurances that your ducts can handle that kind of airflow.
11-15-2005, 12:04 PM
Isn't that to big? It sounds too big but only a load calc can tell.
What are the advantages & disadvantages to putting in an oversized unit? Advantages=0, Disadvantages= uncomfortable air, mold problems, and possible compressor failures.
Will I be blown out by rushing air when the system is on?
This is a result of the ductwork design and system cfm, not tonnage.
Will I spend more $ on electric costs? No, however it will not be comfortable if sized improperly.
Get a load calc professionally done.
11-15-2005, 02:46 PM
I agree with the above, except for one point- an oversized system will cost more in utility bills. These systems take several minutes of running before they can reach any meaningful level of efficiency, and oversized systems rarely get to run long enough continuously to get to the efficient stage.
The lack of comfort produced by an oversized system (inadequate dehumidification) typically leads people to set the thermostat to lower temperatures than they would otherwise, which pushes the utility bills higher still.
11-15-2005, 03:23 PM
Big /Way over sized = Will short cycle on off on off on off?
Think of as putting a jet engine in a small VW bug and just going to the store for milk or the paper every day.
Over sized a little too much = will short cycle, bump on off?
Think of driving a tractor trailer to get milk or the paper every day.
Sized just right = energy efficient no short cycle, runs on the maximum time and shuts down for the maximum time.
Think of driving to get the milk and paper in the VW bug
11-15-2005, 05:33 PM
Here in Lanc, PA, that would be grossly over sized.
Where are you located?
11-15-2005, 08:04 PM
If yur in the south, it is not too big.
What yur contractor is telling you is that he recommends a 2.5 ton system with an oversized indoor coil ( 3 ton size )
With 960 sq ft, rule of thumb would be 2 ton, but an upstairs area generally gets warmer du to the warmer air from downstairs rising to the upstairs, so the upstairs will have more heat to 'condition'. I. personally don't like the idea of the larger indoor coil,( I know it is suppose to make the system more efficient ) but I have never installed one either. I would prfer to go with the 2.5 indoor coil for the humidity removal, if nothing else.Either way, if in the south, I wouldn't go any less than 2.5 ton - to insure comfort.
Hope this helps,
tinknocker service tech
11-15-2005, 08:14 PM
i agree with Born on this. Only need add is do a load calculation
11-16-2005, 04:06 PM
Thanks for all the replies! We live in Atlanta and we do have a wide stairway so we get a lot of air moving up and down the stairs.
11-16-2005, 04:30 PM
Have your contractor do a load calc, or do your own, by clicking the hvac calc tab at the top.
If 2.5 tons is over sized, you'll have alot of humidity trouble.
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