Any BH know about whole house Dehumidifier?

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riley42
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Any BH know about whole house Dehumidifier?

Post by riley42 » Fri Jun 05, 2015 11:31 am

I am trying to see if a whole house dehumidifier is financially a good investment, as the cost may be less than replacing wooden floors, carpet, etc when the humidity in our house stays above 60% during the summer, even with the AC running. But my question for the scientists is if the unit is set for a certain relative humidity %, that will change from winter to summer. In other words, if the temp is warmer in the summer, then the absolute amount of moisture in the air can be higher, even though the relative humidity levels are lower than than the winter. In the colder months, the relative humidity may be very high, but the actual amount of moisture may be very low, as I understand it. So the unit would be running more in the winter if it is set at, say, 45% relative humidity, even though the amount of moisture it removes would be low. I just didn't know if there was anyone with experience that has a whole house unit and if it was more expensive to run in the winter when it would not be needed as much.
Thank you very much for your time and expertise.
Last edited by riley42 on Fri Jun 05, 2015 11:34 am, edited 1 time in total.

Jack FFR1846
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Re: Any BH Scientists know about whole house Dehumidifier?

Post by Jack FFR1846 » Fri Jun 05, 2015 11:33 am

It is called "central air"
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jebmke
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Re: Any BH know about whole house Dehumidifier?

Post by jebmke » Fri Jun 05, 2015 11:41 am

If your house is reasonably well sealed and the AC is sized right, you shouldn't be at humidity levels of 60%. Is you house over a basement, crawlspace or slab?
When you discover that you are riding a dead horse, the best strategy is to dismount.

FandangoDave5010
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Re: Any BH know about whole house Dehumidifier?

Post by FandangoDave5010 » Fri Jun 05, 2015 12:35 pm

I just replaced my A/C humidifier with a new Aprilajre Model 800 Steam Humidifier. I use it all year to maintain a 30 - 35 % humidity in the house. The floors are solid oak throughout the house and have never warped except when flooded from a bathroom sink. They warped pieces have pretty much returned to their original shape. I live in Northern Nevada where it is neither humid, wet nor overly hot.

I lived in New Jersey for 40 years and had 1 ceiling fan in the kitchen and a window A/C in the downstairs TV room. I ran a big humidifier from Sears during the winter and a big dehumidifier during the summer. We had solid oak floors upstairs and they swelled against doorways and walls during the summer and leveled down during the winter. Downstairs, we replace carpeting with ceramic tile which mades the rooms clammy when the window A/C was on. A popular house design of its time, modular walls and windows plus solid wood deck ceilings and floors made it impossible to retrofit with central A/C. (As those in the Northeast know, hot water baseboard heating cannot accommodate A/C.)

As another BH suggested, central A/C is the answer. I would suggest adding a steam humidifier, for about $2,000 more.

DSInvestor
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Re: Any BH know about whole house Dehumidifier?

Post by DSInvestor » Fri Jun 05, 2015 12:51 pm

My neighbor in New Orleans changed her central AC system last year. The new system was the same size as the old system (2 ton I believe) but the new air handler blows air at a lower speed. The new system takes a little longer to get to target temperature but it does a much better job of controlling humidity. She is much more comfortable now.

Does the air handler in your current AC have an option for slower fan speed?
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riley42
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Re: Any BH know about whole house Dehumidifier?

Post by riley42 » Fri Jun 05, 2015 1:08 pm

Thanks for all your answers. Our house sits on a crawlspace. And, unfortunately, our AC system only has one fan speed. Sounds like our insulation around the windows may be lacking if our humidity levels sound high to some of you. We keep the temp set at 77....maybe that is too high?

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Re: Any BH know about whole house Dehumidifier?

Post by rob » Fri Jun 05, 2015 1:15 pm

I bought a serious one @ 2 years ago and it's made a HUGE difference. We had rock ledge everywhere and the moisture was causing a lot of issues.... put plastic over the rock, concreted some of the dirt and ran a really efficient dehumid (@110pints). Caused a bit of an uptick in electric but well worth it. It was expensive ~ 2K but otherwise happy (ping me if you want model info as don't want to post specific manufacturers/websites).
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basspond
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Re: Any BH know about whole house Dehumidifier?

Post by basspond » Fri Jun 05, 2015 1:19 pm

I would get your system checked out. When we first moved into our just built house the attic was almost as cool as the house due to all the leaks in "vent piping".

Globalviewer58
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Re: Any BH know about whole house Dehumidifier?

Post by Globalviewer58 » Fri Jun 05, 2015 1:23 pm

Excess moisture may be migrating from the crawl space into the living space. Installing a layer of plastic sheeting on the floor of the crawl space is current building practice. You might have the crawl space inspected to determine if plastic sheeting covers the area. If the space allows access you should consider having this done.

ralph124cf
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Re: Any BH know about whole house Dehumidifier?

Post by ralph124cf » Fri Jun 05, 2015 1:37 pm

If you have a crawl space, this may be where much of your moisture is coming from. Covering exposed ground in the crawl with a plastic liner will reduce the moisture in the house. Also be sure that the crawl space has adequate ventilation.

I run a 70 pint dehumidifier 24/7 for the five warm months of the year in my basement to keep the upstairs humidity down to 40%. In the winter, both furnaces have humidifiers running to keep the humidity up to 30%.

Do you live in the deep south? Do you need heat in the winter, or do you still need to run your air conditioner many days? I could easily understand someplace like New Orleans or Key West having this type of problem.

The idea is always to keep the humidity as close as possible to constant. If you keep your indoor temperature at 77F then the dehumidifier won't know if it is summer or winter.

One consideration with any large capacity dehumidifier is getting rid of condensate. You would have to empty the condensate pan every two hours. You need to set it up in such a way that the condensate can drain by gravity into your house plumbing. You could set it on a sturdy shelf in the laundry room to drain into a laundry tub, or add a Y fitting to your washing machine drain. If your air conditioner evaporator is inside the conditioned envelope, you could use a Y fitting and put the dehumidifier next to the air conditioner condensate drain line.

Ralph

jebmke
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Re: Any BH know about whole house Dehumidifier?

Post by jebmke » Fri Jun 05, 2015 1:43 pm

ralph124cf wrote: Also be sure that the crawl space has adequate ventilation.
Actually, the current thinking is that the crawl space should be sealed off as much as possible. Vents from the outside bring in outside moisture which condenses in the cooler space.
When you discover that you are riding a dead horse, the best strategy is to dismount.

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Slick8503
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Re: Any BH know about whole house Dehumidifier?

Post by Slick8503 » Fri Jun 05, 2015 1:52 pm

It's possible your A/C system is oversized and is short cycling. This does not allow the system time enough to reduce the humidity in the air. The one caveat to that is if your climate is temperate with high humidity. The latter is a problem in my climate in the spring time. The outside temp is in the 70s but rainy many days. This is where a dehumidifier can make sense. If your humidity stays in the 60s in the summer when your a/c is running, your a/c system is probably too large for the amount of conditioned space you have.

nordsteve
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Re: Any BH know about whole house Dehumidifier?

Post by nordsteve » Fri Jun 05, 2015 2:06 pm

Agree with Slick8503 about the sizing on your AC unit. Also agree with poster suggesting plastic over the dirt in the crawl space. Finally, make sure that you're getting water away from the foundation of the house.

Jonathan
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Re: Any BH know about whole house Dehumidifier?

Post by Jonathan » Fri Jun 05, 2015 2:06 pm

Something is wrong here. Your house shouldn't be that humid. At 60% you're asking for mold.

Yes, 77 is high.

ralph124cf
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Re: Any BH know about whole house Dehumidifier?

Post by ralph124cf » Fri Jun 05, 2015 2:07 pm

jebmke wrote:
ralph124cf wrote: Also be sure that the crawl space has adequate ventilation.
Actually, the current thinking is that the crawl space should be sealed off as much as possible. Vents from the outside bring in outside moisture which condenses in the cooler space.
I would think that this recommendation would be location specific, taking soil and water table height into consideration.

Ralph

riley42
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Re: Any BH know about whole house Dehumidifier?

Post by riley42 » Fri Jun 05, 2015 2:24 pm

Thanks again for all your suggestions. I think we may get a home inspector to come and look at the AC unit if it is too large for our house. We live in Greenville, SC, so it it humid, but not as bad as the coastal areas. Appreciate all your thoughtful suggestions.....

strafe
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Re: Any BH know about whole house Dehumidifier?

Post by strafe » Fri Jun 05, 2015 2:48 pm

riley42 wrote:unfortunately, our AC system only has one fan speed.
Are you sure about this? every old air handler I've seen has 3-4 different fan speed options to tune the airflow to the ductwork and dehumidification requirements. These should be indicated on the wiring diagram.

simpsonlang
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Re: Any BH know about whole house Dehumidifier?

Post by simpsonlang » Fri Jun 05, 2015 3:00 pm

My AC unit is over sized but that was due to horribly leaky ducts. So after I sealed them and better insulated my house I ended up with higher humidity in the winter, Florida winters can be mild enough to not need heat or AC. So I bought a DH150A100 TrueDRY DH150 Whole House. I ran the supply and the return of it into the return of my AC handler. You can wire it with it's own controller or into the controller of your AC unit. If you do a separate controller then you likely need it's own duct runs. I ended up replacing my AC temp controller with one that can accept wires from the DH150. This way when it turns on it also turns on the AC units fan to help circulate the air. I'm able to maintain any humidity level I want but I leave it at 60%. Mine been installed since Dec 2009 and aside from replacing filters nothing has been needed to work on it.

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Re: Any BH know about whole house Dehumidifier?

Post by Jonathan » Fri Jun 05, 2015 3:16 pm

riley42 wrote:Thanks again for all your suggestions. I think we may get a home inspector to come and look at the AC unit if it is too large for our house. We live in Greenville, SC, so it it humid, but not as bad as the coastal areas. Appreciate all your thoughtful suggestions.....
The home inspector is, in part, incentivized to claim that you need a new AC unit. Then he can refer you to an HVAC contractor in his network, who will then quid pro quo the inspector by supplying him with future referrals.

I think you're already on the right track by asking people in this forum, because they're incentivized to boost their forum reputation by providing you with good advice, and, in most cases, don't have a viable economic incentive. For a more detailed or technical explanation, you might consider a dedicated HVAC forum, like HVAC-Talk.com.

I imagine you already know all of this, but it's still worth mentioning.

riley42
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Re: Any BH know about whole house Dehumidifier?

Post by riley42 » Fri Jun 05, 2015 3:30 pm

Jonathan---you are absolutely correct in that the inspector may not have the proper fiduciary responsibility to me in his recommendations. Thank you for the other forum link.

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Re: Any BH know about whole house Dehumidifier?

Post by Ping Pong » Fri Jun 05, 2015 3:45 pm

There are air-conditioners that can automatically slow the system down (based on a humidity sensor) to give it a chance to get enough moisture out of the air. Some even have split-valves in the interior coil so that the system can cool (to dehumidify) and heat at the same time to prevent the system from over-cooling the air while trying to get the moisture out. The Daikin Quaternity is one system that does this. A downside is they can't remove humidity from a room that is below 68 degrees. Cold rooms are usually dry, not humid, so that's not usually a problem. Because there is no outside coil, a dedicated dehumidifier adds heat to the room, which may be unwanted. You can end up paying for electricity to dehumidify (which adds heat) and then pay again to cool the room back down.
Last edited by Ping Pong on Fri Jun 05, 2015 3:49 pm, edited 1 time in total.

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Re: Any BH know about whole house Dehumidifier?

Post by whatusername? » Fri Jun 05, 2015 3:49 pm

Slick8503 wrote:It's possible your A/C system is oversized and is short cycling. This does not allow the system time enough to reduce the humidity in the air. The one caveat to that is if your climate is temperate with high humidity. The latter is a problem in my climate in the spring time. The outside temp is in the 70s but rainy many days. This is where a dehumidifier can make sense. If your humidity stays in the 60s in the summer when your a/c is running, your a/c system is probably too large for the amount of conditioned space you have.
This. Also, you might look at your thermostat - depending on your system you may be able to add a thermostat/humidistat combo (also called a "thermidistat" which will trigger the A/C to run long enough to bring down the humidity. Downside: not very energy efficient and it can over-cool your house too.

60% RH isn't great, but it's not horrible as long as it doesn't persist too long (like all summer...).

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Re: Any BH know about whole house Dehumidifier?

Post by ralph124cf » Fri Jun 05, 2015 3:54 pm

Ping Pong wrote:There are air-conditioners that can automatically slow the system down (based on a humidity sensor) to give it a chance to get enough moisture out of the air. Some even have split-valves in the interior coil so that the system can cool (to dehumidify) and heat at the same time to prevent the system from over-cooling the air while trying to get the moisture out. The Daikin Quaternity is one system that does this. A downside is they can't remove humidity from a room that is below 68 degrees. Cold rooms are usually dry, not humid, so that's not usually a problem. Because there is no outside coil, a dedicated dehumidifier adds heat to the room, which may be unwanted. You can end up paying for electricity to dehumidify (which adds heat) and then pay again to cool the room back down.
It seems to me that this split valve is doing the same thing that your are warning about on the dedicated dehumidifier, spending energy to heat the place as it cools to dehumidify. My understanding is that a single purpose machine is usually more efficient at its job than a multipurpose machine.

Ralph

Ping Pong
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Re: Any BH know about whole house Dehumidifier?

Post by Ping Pong » Fri Jun 05, 2015 4:37 pm

ralph124cf wrote:It seems to me that this split valve is doing the same thing that your are warning about on the dedicated dehumidifier, spending energy to heat the place as it cools to dehumidify. My understanding is that a single purpose machine is usually more efficient at its job than a multipurpose machine.
Yes, the when the split-coil valve turns on, it acts very similarly to a dehumidifier. It only does this when it needs to keep the room from getting too cold. When it's hot and needs to cool the room, it'll cool slowly (or fastly, if required) to make sure it gets the humidity out before cycling off.

If you have a dehumidifier and it's too hot, it will dehumidify and heat the room. So it's accomplishing one goal at the expense of another.

If you had a dehumidifier and an A/C, you'd want A/C to work when it's too hot with the side effect of dehumidification. Once the room was no longer warm, you'd want to turn off the A/C and turn on the dehumidifier if there were still moisture that needed to be removed. This is what these fancier air conditioners do.

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Re: Any BH know about whole house Dehumidifier?

Post by edge » Fri Jun 05, 2015 5:28 pm

77 is probably too warm.

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Re: Any BH know about whole house Dehumidifier?

Post by ehec » Sat Jun 06, 2015 10:55 am

Can't comment on the AC situation, but i do have experience with whole house dehumidifiers, specifically the Honeywell DR series ("TrueDry" is what they call them). These units are not very expensive (~$1000-2000), not very heavy (i ordered my DR 65 online shipped by UPS, believe it or not) and are absolutely incredible. The lighter-duty models like the DR 65 actually do not need to be installed in-line with the duct work (though can be) and can actually just be plopped down in a room you want to dehumidify and they will work in "standalone mode," relatively quietly to boot. As you go up to bigger models like the DR 90 you will find that in general you will need to wire them to some kind of control panel to control them, and that they probably need to be in-line with the duct work.

The 65: http://yourhome.honeywell.com/home/Prod ... t/DH65.htm

I think these units are a great investment; i personally find it to be much more pleasant when the humidity is around ~35% (so, on the low end), and can't stand that sticky feeling at higher humidity.

As to your science question about relative humidity vs the water-concentration in the air: You are right that at high T a given water concentration will correspond to a lower relative H than at low T. Relative humidity is a complicated concentration scale to use because of this, but it is closer to mimicking what you "feel" at any T than a direct measure of water concentration. The relevant T for the relative H inside your house is the T inside your house, not outside. Presumably this does not change too wildly summer<->winter. In the winter there is less water around both inside and outside and so it will spend most of its time in the winter off. It will be much cheaper in the winter.

In any event, you will have to buy about 10 whole house dehumidifiers before you begin to approach the cost of "replacing wooden floors, carpet, etc."

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