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Heating & Air Conditioning

Finished basement HVAC plan

12 years ago

I have a new home that I'm getting started on the basement. I have a 3.5 ton 13SEER/7.7HSPF Tempstar HP with a 92% nat gas furnance backup. Currently the house is all one zone. The first floor is about 1600sqft and the second is about 1200sqft. Conditioned space in the basement will be about the same as first floor.

My plan is to zone the house into three zones; basement, first, and second floor. The first and second floors can be zoned with two dampers. I planned to run basicly the same system of vents and returns as the first floor.

I see a lot of posts about how the basement doesn't need much HVAC, but in my last basement I didn't have nearly enough and it got really hot while hosting parties. Does anyone see anything wrong with this plan. I'm going to be using Honeywell equipment.

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Comments (3)

chuckfh
12 years ago
Zoning has its place. In the scheme of HVAC application. This one seems a little dubious. But get with Jackson Controls. They are experts with zoning. My thoughts are, a little tricky with available static pressure needs when a long call for cooling from from each zone at the same time..will at some point lose temperature control.
david_cary
12 years ago
You are going to have to have it setup so that 2 out of 3 zones are open at all times. Then it may be alright. If only 1 zone calls, the airflow will be too much for that ductwork. If 3 zones call, you may have issues with too little flow for the distant areas - although this is less likely to be a problem compared to just having 1 zone open.

You really can't have enough a/c for a party with most residential systems. You would have to double the ductwork/registers for the basement to put all 3.5 tons down there at once. You could do that and I did something similar. I mostly did it for quick heating when we wanted to go downstairs in the winter. I haven't set up the dampers yet so I can't say how it works. Try to remember to turn the stat down a lot before parties. I haven't had a party in the basement but you should do pretty well by overcooling it ahead of time.
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If the AC condensers are 2 and 2.5 tons then it does not appear they are over sized for a 3700 sf foot house in central Florida. It is unusual that the second floor is more humid than the basement. Have you checked the attic lately? You mentioned the roof has spray foam. Was that applied to the roof deck? Do you have adequate attic ventilation? If the attic ventilation is poor then the rising warm humid air may be rising and not able to escape up through the attic. If this is happening then you need to add attic ventilation. I can't advise you whether spending $600 on an "engineer" to assess your house and write a report is money well spent or not. You should go out and buy hygrometers to measure the humidity at all the levels. I like that type that also measure temperature. I have the AcuRite Humidity-Monitor. It is fairly accurate and inexpensive. Buy one for each level and monitor the temperature and humidity. The fact that you have to lower the temperature to 72 degrees shows the humidity is high and your trying to compensate with a lower temperature. The goal is to get the humidity down to 40%. If you can do then you should be comfortable at 75 degrees and possibly higher. Keep us posted. This is an interesting situation and I would like to see how it plays out.
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blk94f150
Original Author
12 years ago
When we were building the house, we could have zoned it for $2,850. That would be basement and first floor on a zone (10 4x10 registers) and second floor on a zone (9 4x10 registers). Other than that there would be no difference from what I have now.

For my basement I had planned on running 9 4x10 registers. One in storage, one in 1/2 bath, three main living/tv area, two in bar, and two in fitness (not likely) or pool room. That makes nine and I'll put in a return equal to the input of the area. I also plan on a bypass and DAT sensor to cover high pressure or extreme temps.

So I don't see what the problem is unless what they put in normally is bad to begin with. I was also hoping for the secondary benefit of lowering my second floor temp as it's always about three degrees higher than floor one.

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