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Discussion Starter #1
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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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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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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Check into Therma-stor. they also make some of the Honeywell models.
 
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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 :whistling2:
 

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Discussion Starter #8
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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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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Discussion Starter #10
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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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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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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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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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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Discussion Starter #16
The markup for the unit that was quoted by my contractor was around $1,200. Granted, some is markup, and some is labor, but I think that quote was to put a unit in the basement alone. I'm just not sure I'm willing to spend that much to pay someone to do it. It seems like it would be pretty straight forward to put one in. Mostly ductwork and wiring the controller. I would probably need a relay to stop the dehumidifier from running when the HVAC is on as well. A drip pan, and a level switch.

At any rate, how would someone approach a whole home dehumidifier in a house with a zoned HVAC such as mine? It doesn't seem like there is a good way to supply fresh/dehumidied air to several rooms without it being a ducting nightmare.

BTW, I appreciate all the feedback, and I hope everyone has a very merry Christmas!
 

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Some is mark up, some labor, some misc material, some is for first year labor warranty.
 

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A freestanding dehumidifier in the basement can be a DIY project. Some of the better freestanding dehumidifiers can be ducted. The freestanding dehumidifiers are designed to be quickly and easily installed, but they do not provide many of the features of the whole house units. Installing an efficient dehumidifier is key to saving money in the long run - just as it is with heating and air conditioning systems. The cheapest first cost unit may be significantly more expensive when you consider the cost to operate over time.

Whole house dehumidifiers are equipped with controls that can integrate with your existing HVAC controls. Installing a whole house dehumidifier in a house with zoned AC is possible - the installer must understand what you want from your HVAC system and they must understand the zone AC control as well as the dehumidifier control in order to deliver the comfort and indoor air quality you desire. This is what you are paying for when you have a contractor install your system(s). You are paying someone that has the knowledge and ability to install it correctly.

You are doing the right thing by asking questions and becoming educated about your house and the mechanical systems within. Keep asking questions - this will help you understand what you want and what is possible. It will allow you to determine if you want to undertake a DIY project, or if you should hire a contractor. You will be able to intelligently converse with contractors and make informed decisions.
 

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Discussion Starter #19
I took another look at my HVAC ducting near my AHU, and it looks like both returns in my house are connected to a common plenum. There is a short duct run from the master and a longer run from the 2nd floor return that acts as the "main" return for the rest of the house. Would a dedicated return for the dehumidifier offer any benefit with this configuration? It looks like connecting to the HVAC return near that common plenum will draw air from both returns in the house, one of which is located near the top of my centrally located stairs and is open to the vast majority of the house including the basement (our house has an open floor plan) via that stairway (our house has an open floor plan) .
 

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The answer is maybe. AC returns are often undersized for the air handler they are connected to - adding a dehumidifier to the return which can run at the same time as the AC system will lower the efficiency of both the dehumidifier and the AC system as they are both fighting for the return air when they are running.

The dehumidifier moves less air than the air handler and may short circuit back through the air handler if the air handler fan is not running. Some dehumidifiers are installed in the way you suggest (in parallel with the air handler) with an interlock that runs the air handler fan at a low speed when the dehumidifier is operating to prevent this problem. This solution requires that the air handler fan consume electricity to operate at low speed whenever the dehumidifier operates. The dehumidifier will have a backdraft damper installed to prevent the air handler from short circuiting through the dehumidifier when the dehumidifier is not operating as well.
 
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