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Whole house dehumidifer vs. variable speed AC

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RandB

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Discussion starter · #1 ·
We're replacing the furnace and AC in our 1650 square foot ranch house in Wisconsin. Based largely on what I've read here I believe whole house dehumidifiers are a good solution for nights when the temperature is over 70 and the dew point is high. Unfortunately our furnace room is kind of cramped and fitting in the unit and the associated ducts would be pretty tight. For about the same money I could upgrade to a variable speed AC (looking at Lennox XC20) that can ramp down to something like 1 ton for a 3 ton unit. Is this a reasonable solution?

Richard
 
#3 ·
RandB said:
We're replacing the furnace and AC in our 1650 square foot ranch house in Wisconsin. Based largely on what I've read here I believe whole house dehumidifiers are a good solution for nights when the temperature is over 70 and the dew point is high. Unfortunately our furnace room is kind of cramped and fitting in the unit and the associated ducts would be pretty tight. For about the same money I could upgrade to a variable speed AC (looking at Lennox XC20) that can ramp down to something like 1 ton for a 3 ton unit. Is this a reasonable solution?

Richard
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Just be careful--VS works well where I am as it is dry climate--when a VS compressor ramps down, your indoor coil does not, resulting in not so good dehumidification on low sensible day
 
#4 ·
RandB said:
We're replacing the furnace and AC in our 1650 square foot ranch house in Wisconsin. Based largely on what I've read here I believe whole house dehumidifiers are a good solution for nights when the temperature is over 70 and the dew point is high. Unfortunately our furnace room is kind of cramped and fitting in the unit and the associated ducts would be pretty tight. For about the same money I could upgrade to a variable speed AC (looking at Lennox XC20) that can ramp down to something like 1 ton for a 3 ton unit. Is this a reasonable solution?

Richard
Click to expand...
If you want 50%RH throughout your home during cool outdoor temps and high dew points, go with a small whole dehumidifier. You will get 50%RH with low/no cooling loads or even with a/c off. The idea that a/c can maintain 50%RH without a steady 1-2 ton of cooling is mechanically impossible. Reheat on the a/c or supplemental dehumidification is a must. A high efficiency dehumidifier like the Ultra-Aire 70H would be ideal. Its the size of a hat box.
Currently the basement %RH in green grass climates is on the rise. We are approaching 60%RH and we are a month away from any cooling loads. For comfort and low energy consumption, a small whole dehumidifier is best. You also can avoid complicated multispeed a/cs.
Keep us posted about the %RH control regardless which way you go. Where in WI?
Regards Teddy Bear
 
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Discussion starter · #7 ·
lkapigian said:
Just be careful--VS works well where I am as it is dry climate--when a VS compressor ramps down, your indoor coil does not, resulting in not so good dehumidification on low sensible day
Click to expand...
So you're saying that the AC on its lowest setting might be running at one ton but with a three ton coil? What effect would that have?
 
#9 ·
Coil runs warmer can mean lower latent capacity which is humidity removal. And less air gets to distant rooms, especially 2nd floor with furnace in the basement. We get a lot of complaints about warm upstairs even with 100% blower. I'd hate to think about how little air will make it to the 2nd floor with 400 CFM out of a 3 ton on low.
 
Discussion starter · #10 ·
We are in Madison. I've been having a difficult time trying to find a contractor that believes in doing any measurements. I ran loadcalc.net and got slightly under 20,000 BTUH for the cooling load. I finally convinced one contractor to run a manual J (with my inputs for insulation amounts, window sizes, etc.) and they got 15,000 BTUH cooling load. But they strongly advise against installing anything smaller than 2.5 tons. Our original AC was 2.5 tons, since then we have insulated the attic and installed low-E windows.

For me it seems the path of least resistance is to either go with a 2.5 ton single stage AC and a whole house dehumidifier, or a variable speed so the exact rating isn't so important and I can stop arguing with them about sizing. I'm just trying to avoid overcooling the house at night to get the humidity down. Which sounds exactly like we need the dehumidifier, but if we could get similar results with a variable speed AC and avoid taking up the extra space in the basement that would be preferable.
 
#11 ·
RandB said:
We are in Madison. I've been having a difficult time trying to find a contractor that believes in doing any measurements. I ran loadcalc.net and got slightly under 20,000 BTUH for the cooling load. I finally convinced one contractor to run a manual J (with my inputs for insulation amounts, window sizes, etc.) and they got 15,000 BTUH cooling load. But they strongly advise against installing anything smaller than 2.5 tons. Our original AC was 2.5 tons, since then we have insulated the attic and installed low-E windows.

For me it seems the path of least resistance is to either go with a 2.5 ton single stage AC and a whole house dehumidifier, or a variable speed so the exact rating isn't so important and I can stop arguing with them about sizing. I'm just trying to avoid overcooling the house at night to get the humidity down. Which sounds exactly like we need the dehumidifier, but if we could get similar results with a variable speed AC and avoid the extra taking up the extra space in the basement that would be preferable.
Click to expand...
I'll do your Manual J and S email is in my profile if interested. But I am betting 2 is more than enough--if your 2.5 cycled on the hottest days, it is oversized--Do not go 3 just because, verify don't let them guess
 
#17 ·
RandB said:
We are in Madison. I've been having a difficult time trying to find a contractor that believes in doing any measurements. I ran loadcalc.net and got slightly under 20,000 BTUH for the cooling load. I finally convinced one contractor to run a manual J (with my inputs for insulation amounts, window sizes, etc.) and they got 15,000 BTUH cooling load. But they strongly advise against installing anything smaller than 2.5 tons. Our original AC was 2.5 tons, since then we have insulated the attic and installed low-E windows.

For me it seems the path of least resistance is to either go with a 2.5 ton single stage AC and a whole house dehumidifier, or a variable speed so the exact rating isn't so important and I can stop arguing with them about sizing. I'm just trying to avoid overcooling the house at night to get the humidity down. Which sounds exactly like we need the dehumidifier, but if we could get similar results with a variable speed AC and avoid taking up the extra space in the basement that would be preferable.
Click to expand...
Why not try to get the contractor to commit to putting in writing the maintaining 50%RH throughout the home part during cool damp weather?
Just kidding. We are approaching the point in WI where the home %RH is starting to rise. In fact my WI home basement is +55%RH right now. Time to activate the small whole house dehumidifier. I also suggest a small amount of fresh air if your home is moderately air tight. During the calm winds of S/S/Fall fresh air during occupancy improves the indoor air quality of most WI homes.
You could also stop by our MSN Lein Rd office/plant.
Keep us posted.
Regards Teddy Bear
 
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Discussion starter · #18 ·
At this point I'm leaning toward the Lennox XC16 2 stage AC at 2 tons. Along with the EL296V two stage furnace. I will try that and add the whole house dehumidifier if needed. Is there any major advantage to going with the Lennox communicating thermostat for 2 stage gear, or am I free to spec out a 24 volt thermostat? Dealer likes Honeywell, I'm intrigued by the Ecobee3 (which they will install if I ask for it), mainly because I dabble with home automation and it integrates well with that stuff (Lennox does not).
 
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