Is this Sized Right?

[JPSilver]

I am contemplating buying a newly constructed townhouse in Sevierville, TN.

The unit has 3200 sq. ft. (2400 down, 800 up). It has Pella Low-E double pane windows, R21 in exterior walls with 24" OC studs and 5/8" drywall exterior walls and ceilings. It has radiant barrier decking and R40 in the attic with full soffit ventilation and ridge vents. They are putting in an Amana 16-SEER 3-ton A/C unit and a 70,000 BTU 95% efficient natural gas heater. The house is ENERGY STAR CERTIFIED.

I have lived in Texas and Oklahoma all my life and you would roast here during the summer in a house that size with only 3-tons. My current house in Dallas is 18 years old, single story, 2400 sq ft with a Carrier 4-ton. It does a very nice job even at 100+, I believe my heater to be 80,000 with 80% efficiency. It has R13 walls and R26 attic insulation.

East Tennessee normal summer temps are in the 80s with higher humidity. 90s are the exception and don't occur often. The nighttime temps usually fall back into the low 70s and upper 60s.

Are they anywhere close on the sizing?

I have been lurking on this board for awhile and have added quite a bit to my HVAC knowledge as a non-professional.

[pwg11386]

without visiting the house and doing load calculations there, i couldnt tell you. It does sound reasonable though. There is a huge difference between the insulation of both houses, and i'm betting the windows as well. Ask the engineer how he arrived at this tonnage and if he did a load calculation. I don't see many builders put in 16 seer equipment without investing the time and money for proper load calculating.

[Cool_Air]

I am contemplating buying a newly constructed townhouse in Sevierville, TN.

The unit has 3200 sq. ft. (2400 down, 800 up). It has Pella Low-E double pane windows, R21 in exterior walls with 24" OC studs and 5/8" drywall exterior walls and ceilings. It has radiant barrier decking and R40 in the attic with full soffit ventilation and ridge vents. They are putting in an Amana 16-SEER 3-ton A/C unit and a 70,000 BTU 95% efficient natural gas heater. The house is ENERGY STAR CERTIFIED.

I have lived in Texas and Oklahoma all my life and you would roast here during the summer in a house that size with only 3-tons. My current house in Dallas is 18 years old, single story, 2400 sq ft with a Carrier 4-ton. It does a very nice job even at 100+, I believe my heater to be 80,000 with 80% efficiency. It has R13 walls and R26 attic insulation. :East Tennessee normal summer temps are in the 80s with higher humidity. 90s are the exception and don't occur often. The nighttime temps usually fall back into the low 70s and upper 60s.

Are they anywhere close on the sizing?

I have been lurking on this board for awhile and have added quite a bit to my HVAC knowledge as a non-professional. :eek2:With as much insulation that you have it my or may not be close with out doing a manual J ,S and check D it's only gussing If you do all this and the ducts wrong its a no go! To little uncomforable in low and hi temps. To large short cycles hi hum. hi ligh bills unit could fail early. This is just my fillings. hope this helps. Good luck.

[BaldLoonie]

Dang, that place is INSULATED! Might be oversized!

Pretty rare to see undersized stuff. Upstairs may not cool that well with 1 system unless the duct system was well designed. But usually well designed duct systems and RNC don't go hand in hand.

[George2]

Dang, that place is INSULATED! Might be oversized!

Pretty rare to see undersized stuff. Upstairs may not cool that well with 1 system unless the duct system was well designed. But usually well designed duct systems and RNC don't go hand in hand.

B.L.

That's a great point regarding the second floor. He might move in, not be able to cool the second floor, and "think" the A/C is to small when in fact it's the duct work.

Sounds like a good candidate for zoning.

[pwg11386]

Hate to see a zone that small on such a large system

[acwizard]

No doubt that this home is well insulated. I would ask the builder for the energy calcs on this home. Here is just another thought, As houses become better insulated and become tighter, the energy that is required to heat or cool becomes less. The down side of this is the actual air quality in the home. With the size given in relationship to the volume of space in the home, the system would only be changing the air approx. twice in one hour. These figures start to become concerning when no outside air is introduced into the living space. Ventilation rates are just as important as reduction in energy.

[pwg11386]

Well said.

[George2]

Hate to see a zone that small on such a large system

I don't remember the size of this home but I do remember the size of the A/C.

It sound very similiar to this (example) house.

It had a 3.5 ton A/C. The second floor, I believe had 5 (6") supplies. Two bedrooms and a bathroom, again, as I remember it. The point is that the main floor was 3 times larger.

Anyway, I put in a two zone system (no by-pass, I was told was needed) and she is absoultly delighted with it.

She could not A/C the second floor (for her son) before the zoning and now he has his on thermostat.