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Old 12-17-2012, 09:25 PM   #1
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Central Dehumidifier Question


We recently built a home in central Alabama with spray foam insulation. After a long discussion with our HVAC contractor about humidity in tightly built homes, we opted for the variable speed AHU and two-stage compressor for our HVAC (trane units). Fast forward to our first winter, and we've had nearly two months where our HVAC runs very little. I would guess on average it runs for a few minutes once or twice a day, and some days not at all. So there is little to no humidity control. Unfortunately, the humidity outside has been relatively high for most of the winter so far, and the humidity in most of the house stays between 55% and 60% and the master bedroom usually stays between 60% and 65%. Oddly enough, our basement is the driest part of the house as it's only creeped above 55% in the past few days. I run the vent fans, but it's just pulling in humid air from outside.

Should I be considering a central dehumidifier? I'd love to say this type of weather is rare in Alabama, but I'd say this is probably the norm for a good portion of winter and spring.
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Old 12-18-2012, 04:25 AM   #2
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Central Dehumidifier Question


A whole house dehumidifier would be your best bet. Might even want to get one that is a ventilating dehumidifier. So that it can bring in fresh air and dehumidify it before it brings the air in.
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Old 12-18-2012, 06:52 AM   #3
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Any suggestions on a brand or place to get one? My contractor uses Honeywell I believe, but I have very little experience with these.
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Old 12-18-2012, 01:00 PM   #4
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Check into Therma-stor. they also make some of the Honeywell models.
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Old 12-19-2012, 06:52 AM   #5
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Thanks for the feedback. Now, it's off to the Googles!
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Old 12-22-2012, 10:36 AM   #6
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Central Dehumidifier Question


I'd buy a Nortec steam humidifier if I were you, its called the Res Delux. I have one and they work great.
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Old 12-22-2012, 11:20 AM   #7
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Central Dehumidifier Question


My Dad told me when I was about 10 years old that it is really no good to build a house too tight. He used to say that a well built home should be able to "breathe" He also mentioned the pilot lights that ran continuously, and the chemicals use to make rugs, insulation, plywood and such, that dump things into the air that are not good for the average respiratory system. I am sure this came from my mom. She was against spray paint in cans and hair spray way back in the 50's and 60's. She is long gone, but now we know she was right.

When you build a house too tight, and insulate it with an insulation that leeches its blowing chemical throughout its lifetime, an insulation that cuts off any and all pathways to air infiltration, you are asking for trouble, IMHO. You pay more to make the house extremely tight to save energy, then go back and burn energy (Money) to change the moisture content in the air. Kind of ridiculous, dont you think?

Here in MD we constantly have humidity above 65% and it does not seem to bother anyone till it hiits like 70 or so. Maybe it feels different where you live. I know that 70-50 is what commercial buildings shoot for.

Seems to me that it makes more sense to let the house breathe by using an inorganic insulation like fiberglass, which you cant make as tight as foam, and put on a sweatshirt in the winter time, does it not?

You might want to have a air quality survey just for the heck of it, to check for airborne chemicals.

Just My Opinion, I could be wrong
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Last edited by jagans; 12-22-2012 at 11:28 AM.
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Old 12-22-2012, 05:11 PM   #8
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There are lots of threads on the pros and cons of spray foam, so I'm not going to head down that tangent. My main concern is not comfort, as I'm pretty comfortable in a wide range of temps. I'm more concerned with mold growth and possible condensation in the basement. The humidity in our house is generally lower than outside, so even a house that "breathes" would not improve the humidity issue. From what I understand, a RH higher than 70% will start mold growth and then anything above 60% will susstain it.
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Old 12-22-2012, 05:26 PM   #9
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Central Dehumidifier Question


What time of year are you talking about in MD? Humidity levels are way below 65% in the winter, no matter how tight or loose your house is you still need to add humidity if you want to be between 40-50% RH in the winter months which is the ideal RH levels for health. You can also keep your temp 2-3 deg below what you would normally would when you humidify to 40-50% RH. The extra water in the air makes it seem a little warmer.
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Old 12-22-2012, 05:37 PM   #10
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Quote:
Originally Posted by pool View Post
I'd buy a Nortec steam humidifier if I were you, its called the Res Delux. I have one and they work great.
I think I have the other humidity problem the humidity in my house it too high (I think anyway), and here in Alabama it stays that way most of the year. I don't know that I've ever seen a humidifier installed in this part of the country.
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Old 12-22-2012, 05:54 PM   #11
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Quote:
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I'd buy a Nortec steam humidifier if I were you, its called the Res Delux. I have one and they work great.
Why, he wants to remove humidity, not add it.
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Old 12-22-2012, 05:57 PM   #12
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Quote:
Originally Posted by pool View Post
What time of year are you talking about in MD? Humidity levels are way below 65% in the winter, no matter how tight or loose your house is you still need to add humidity if you want to be between 40-50% RH in the winter months which is the ideal RH levels for health. You can also keep your temp 2-3 deg below what you would normally would when you humidify to 40-50% RH. The extra water in the air makes it seem a little warmer.
Depending on the size of the house, and how tight it is, no humidity needs to be added. It needs to be removed. Tight homes seldom need humidity added in the winter. loose homes usually do though.

At low outdoor temps, 50% indoor RH is too high, and can cause damage to the homes structure.
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Old 12-23-2012, 04:53 PM   #13
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Central Dehumidifier Question


Unfortunately, the best air conditioner will only remove humidity when it is cooling your house. If the temperature inside your house is comfortable without the AC system running, you have to over-cool your house to force the AC system to operate and remove humidity. Most houses in your climate do not have humidity problems in the summertime when the AC system is operating much of the time, but they struggle in the winter when the days are shorter and the outdoor temperatures are lower (but the dew point outside is still high). Adding an efficient dehumidifier is a good choice to provide comfort inside your house for a reasonable cost.

The Ultra-Aire line of whole house dehumidifiers are the premier high efficiency units in the market now. These dehumidifiers are assembled in the USA.

http://www.ultra-aire.com/

These units are designed to filter and dehumidify the air in your house. The Ultra-Aire units will also bring fresh air into your house to provide ventilation and positively pressurize your house (which is a good thing in your climate). They are expensive, but over time the lower cost to operate them (since they operate at high efficiency compared to less expensive dehumidifiers) will save you money.

The company that manufactures and sells the Ultra-Aire units also sells Santa-Fe high efficiency free standing dehumidifiers which can be set and installed by a homeowner. The Santa-Fe units are not ducted and do not provide the ventilation feature of the Ultra-Aire units.

http://www.santa-fe-products.com/
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Old 12-23-2012, 09:18 PM   #14
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Are thee any recommended distributors for these units that sale to the public?

Also, in researching this I'm considering using a ducted unit and connecting to the return in the master bedroom (highest humidity levels in the house) and discharging into the basement supply line. The basement is zoned separately, so I Don't think I will have to worry about circulating much air back through the HVAC AHU. I would be able to connect to the return within a couple feet of the filter, so a very short run there, although the duct to the basement is quite long. Thoughts?

I like the idea of discharging into the basement as the added heat load will just keep the basement closer to the average home temp. Obviously drawing from the master to pull out the most humid air in the house.
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Old 12-24-2012, 01:37 PM   #15
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Central Dehumidifier Question


There are a number of distributors for the Santa-Fe free standing dehumidifiers, just google "Santa-Fe dehumidifier" to see them. The Ultra-Aire and other whole house dehumidifiers are sold by HVAC trade wholesalers and distributors. Properly installing a whole house dehumidifier is not a DIY project and they are usually installed by an HVAC contractor.

The idea of ducting the supply from the whole house dehumidifier into your basement (where the heat is useful) is reasonable. Generally a whole house dehumidifier is installed with a dedicated return in a central part of the house (hall, foyer, living room) that is connected to the other rooms in the house. You want the air from the supply to be able to flow back to the return through the house so that rooms are not pressurized and depressurized when the dehumidifier is running.

The dehumidifier supply is usually connected to the AC system supply to distribute the dehumidified air to all the rooms in the house. A possible problem placing the return in your master bedroom is that it may depressurize your bedroom (especially with the door closed) and cause (humid) outdoor air to infiltrate into your bedroom. If you plan to have the whole house dehumidifier provide ventilation for your house, many people prefer that the supply go into the bedrooms where people spend most of their time to get the benefit of the fresh air.
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