How to Install a Whole-House Dehumidifier | Ask This Old House 

What do you do when they tell how ac works

What make/model of dehumidifier did you use?

I need to do this now... can you elaborate more. what kind you used? I was looking at a mobile industrial one at Home Depot for $1400. Not sure how loud it would be. I have technically two LOWER floors, bottom one was an old coal room!, it's have mud and soot and MILDEW/moisture. So upper two floors of the house the air quality is horrible. I can't move in til I fix this.

Do you have a basement? Does it get wet? First try to figure out how to redirect the water from your gutters as far away from the house as possible. As for a dehumidifier get a Santa Fe Classic. Expensive, but well worth it.

Portable units can be inaccurate in humidity readings. Their compact size means your humidity sensor might be located in a spot on the dehumidifier that has it reading higher or lower than the actual room. But yes, 35% humidity wouldn't feel very comfortable, especially in Louisiana, you'd feel like your throat and nasal cavity was dried out, your sheets and clothes would get static cling. Then you'd step out of your house into the Louisiana summer air and feel like you're trying to breathe in a fish tank.

Thats what I do got tired of dumping buckets

You can use duct tape to get 100% air seal and then strap it

Old house. Nothing new

you can rent that space out to a college student lol

That's pretty typical even on new construction in the southern USA.

I think you'll find attics are usually about the same size as the house to which they belong...

Lol

Richard mentioned right at the end of the video that it was a matter of personal preference and that the humidistat would be adjustable based on the people and instruments' needs..

I perfer 35-40%. 55% is when mold growth starts to be encouraged. Wood isn't going to start cracking unless you are going to like 20% or less humidity.

Depends on what time a year it is. 55 precent humidity is ok in winter but if it's 80 degrees out 55 precent can feel muggy

@jeff Webb all you need is an evaporative cooler where you're at

@Jeff Webb the moon?

I was sitting here replaying that for a min trying to figure out wtf was happening lol.

@@WheezySalmon I completely miss that the first time and I've been wearing glasses since I was in my single digit years; ~18 years ago. XD

When this was originally recorded smart thermostats didn't exist yet, only the first gen nest existed

a lot of portable dehumidifiers have a built in pump. but they usually only pull out 55 pints a day or so. a house on the coast needs a lot more dehumidifying than that.

My wife and I were in New Orleans a few years ago. It's very humid and rains throughout the day. I'm outside Philadelphia and it's just about the same with humidity here in summer. But they get it almost all year round. Why live there?

@@beebob1279 People live in New Orleans for 2 reasons. Food and Mardi Gras. But since you lived in N.O. then you already know that.

I would imagine that they just piped it into the existing condensation line.

@@andreo Not smart unless you’ve got both units on a float switch, in a pan. The easiest way, imo, is add a float switch to your primary HVAC system. And then you can use your secondary drain for the pan- just cut it, glue a “T” in & discharge it through the secondary drain. Although, you may want to alter the location on the exterior if it’s up high so you don’t have water splashing down all the time. I’d recommend extending the PVC, and then run it into a diverter like you’d use underneath a gutter, to push it out and away from the home’s foundation.

I was thinking the same thing.... the attic gets extremely hot!

@@srlandreneau This attic won't get hot. It's conditioned.

In this case you can custom rigg it. I think the manufacturer defaults to that location in case you're not adding duct to it(like in my case)

It's all about that bass, no treble! 🎶

used HVAC piping

Here in Houston some houses have a drain at the soffits

Also you can plumb to the ac condensation line which is usually plumbed to a bathroom sink

The product manual has the power... typically under 200 watts.

The unit is a mini-AC unit in a box. Evaporation coil (cold), condensation coil (hot), a fan, and a compressor. I wouldn’t know any stats, but being a whole house unit, 2,000 watts (or more) wouldn’t surprise me.

and then it go bust after 2 year if your lucky .... portable AC are disposable pieces of junks nowaday

Portable dehumidifiers have become very effective. I have a Frigidaire that I run 24/7 in the summer drained into the sump. I would not want it in the living space given they are noisy and have a hose connected. Would not want it in my living space.

someone in the comment section mentioned there is a one way flap on the unit to prevent that from happening

Explains how both works. ACs also tend to act as dehumidifiers too. Better vid than I was expecting

It does have a pan where they set the unit that was a pain.

Only if your equipment is large enough to keep up with the set cooling temp could you do this. Most systems that are properly sized aren’t going to cool well with fan speed on low in summer time. Yes, it will dehumidify better. But it may not be able to keep up with the set point on your thermostat.

@justincoard2591 how can I lower the fan speed?? I have 3.5 ton, and AC only runs for about 12 min which I think is not long enough to remove all humidity, which does create high humidity levels in my house. I'd like to try lowering fan speed before installing a humidifier. When you say poor filters, do you mean lowe MERV rating?? I currently use a 5 since I was told the higher the Merv rating, the more air restriction which makes the unit work less efficiently. Is this true??

@@joleaiperlis5347 I mean poor as in dirty. The high merv filters are fine but depending on if you smoke burn candles or have pets, you may have to change them out early than recommended. A 15 minute cycling time can be pretty low depending on your unit and home envelope. I can say some AC units, to even reach peak efficiency to even pull humidity out of the air can take 15 minutes.

His video was about house dehumidification, not attic dehumidification. If you serch yotube for "conditioned attic" you are going to find the answer you are looking for. One solution for attic moisture control, it will be a ridge moisture difiusion port. I hope that the above will help.

I'm a year late, but he states that it is not required to run the air handler in this setup. Yes, you will be adding heat to the house whenever the dehumidifier is running.

@@TFSGEO there is no way the fan in that unit effectively overcomes static pressure in these three main trunks - negligible air movement. as for his blithe statement humidify equalizes across the house, guffaw guffaw, not if you have large house multiple floors and certainly not rapidly ie within a few hours

You’re comment makes sense this installation is just wrong just imagine also when the turn on AC/Heat the air will be blown back to the dehumidifier

@@Melo_Alienware most dehumidifiers have a backdraft damper built in

It depends on the static pressure across the dehumidifier unit. If it's 0.5 inches of water, and the product states it can supply like 120 cfm at that static pressure, it will flow all through the house. However, you can set these up to also turn on the A/C fan when the dehumidifier runs to get extra flow.

You can add both a whole-home dehumidifier for warmer months, and a whole home humidifier for your colder months. Although, I prefer the larger portable humidifiers. Not a fan of pumping moisture into my ductwork.

@@justincoard2591 Why are you not a fan of bypass or fan powered powered humidifiers?

@@Guillotines_For_Globalists I’m just not a fun of any humidifier placed into the duct work. Have seen all sorts of mold and mildew issues bc of them. I prefer using just a standalone humidifier in a room or rooms in the house. Anything not in the ductwork is fine.

At least seven.

yeah. there was a one way flap seen under his thumb at 5:10.

I was wondering the same thing. How will this system not put back-pressure on the AC filter, knocking all the dust back out into the house?

@@andrewhurley7118 no response. I was thinking the same thing. What is stopping the air flow from going backward through the AC blower and back out the return air duct, filter, etc?

@@DCUPtoejuice This is why I recommend installing it at the FURTHEST point of the main trunk like, as far away from the air handler as possible. You’ll still be feeding your supply side ductwork. And most of the air velocity will have gone out to the supply ductwork before it reaches the air handler. Because in this installation, you’re not only pushing the air backwards through your air handler, and out of the HVAC systems air filter. But if you’re also using it in the summer, and the AC system isn’t currently running, you’re blowing that dehumidified air right across a wet HVAC coil, out through the HVAC filter, which in turn then RAISES the humidity in your home. This is the same reason you don’t ever leave your fan in the on position in cooking mode, only should be on auto. Bc if you’re running the fan on constant, when the system isn’t actually cooling, you’re blowing air across a wet coil, thus INCREASING humidity in your home. Fan should ALWAYS be on Auto, not on position, when your thermostat is set to cooling mode.

@@justincoard2591 and THAT is why you have to be abel to trigger the HVAC blower fan when this device his working !!!

He also installed the grill the wrong way at this time lol

I thought that was duct tape. Unless it's a different product

4 years late but they specifically called out the issue is that during autumn and spring the air outside is too humid, bringing air from outside is not viable. I have the exact same issue as in this video.

@@Snutze Then the unit isn't large enough... You can outrun them but it's typically on hot humid days not cool humid ones. Put a temp/humidity or IAQ monitor in and find out!

There’s literally nothing wrong with proper duct tape on the return, as long as you secure it with a large zip tie as well. Duct tape & zip tie on inner lining of flex. Then duct tape and zip tie on outer portion of flex. It passes new construction code in Virginia. And yes, while they should have pulled the flex duct tight, there’s no need for metal 90’s. It’s a dehu man. Also, bringing in unconditioned, humid outdoor air is completely unnecessary as well. This isn’t a commercial application where you need air changes per hour. It’s resi bud. Completely acceptable setup they did.

You can get a larger portable dehumidifier (70 pint) with a pump built in and run a hose to a drain or sink so it runs continuously. Dehumidifiers efficiency goes down as they age.

@@daniel193100 I'm running one in the basement with a pump that leads to the outside now. I just came back from the house yesterday. It's finally drying the place out and cycling on and off to keep with the humidity. But the top two floors are humid. I may have to put one on the first floor too during winter to dry it out up there. The pump can just go into the sink to drain. But a whole house dehumidifier would be much easier

Just get a larger dehumidifier for your basement. And get one with a built in pump. No need for a whole home setup like this if basement is your primary concern. Just be aware, the bigger ones are pretty noisy. And If you have no drains like a sink or something in your basement, pipe the condensate pump to the exterior of the home, and at least a few feet away from the foundation of the home.

is there a way to dehumidify just the attic ? don't connect to the AH, but instead vent the dehu supply to the outside ?

No.

By name, humidifier makes air more humid and dehumidifier is the opposite. Evaporative cooling is also a way to make indoor air more humid, serve similar purpose as that humidifier

Nathan The dehumidifier is just a small air conditioner with the outdoor/condenser coil mounted directly behind the indoor/evaporator coil in the same box. The evaporator coil cools the air below the dew point, which makes the humidity in it condense and that's carried off by the drain, then the now-dry air blows over the condenser, which reheats it before it's returned to the house.

There is a back-flow damper that prevents air going backwards.

The outgoing air from the the dehu SHOULD be going into the supply ducts on the HVAC system. Lol. That’s how it’s designed.

Yeah I cant fathom the logic of people putting these appliances in ATTICS, and to get up there you have to drop those sliding steps down from the ceiling, a real pain in the ass. At my work place they put 3 AC/furnaces in the attic, and to get up to check filters it's a ceiling panel you need to climb up to and crawl up thru. What's worse is it's not conditioned up there, so when it's zero degrees outside it's zero in the attic too and the condensate drains often FREEZE. In the summer it's like 120 degrees up there and the A/C are struggling big time. As if that's not bad enough, the 4" pleated filters they use cost around $40 EACH, and because it's a wood shop the filters barely last a month. Even worse- the contractors put two more units up on the ROOF of the new addition! so to get up there to check filters takes a 20 foot extension ladder, and each unit takes FOUR filters. Being up on the roof that takes a 20 foot ladder to get to is the worst place they could have put the things. People had better use extreme caution with attics, millions of homes and businesses have Zonolite (R) vermiculite insulation in them, that insulation was contaminated by the most deadly form of asbestos known, you go tromping around in an attic with that stuff, and worse- installing ductwork and machines in there and you spread that asbestos throughout the house even more, and evern time you go up there to check filters you stir up even more. Search here for; zonolite asbestos insulation libby Mt or see ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-gnOdJMC67gM.html

Victorian Sculptures I know I managed a couple of stores that had similar AC systems that were in impossible places to change the filters. The ones that were in the ceilings were in the absolute worst places, in the fitting room I don’t understand what these engineers were thinking when they installed.

@@HobbyOrganist A lot of newer homes are doing that. I don't get it either. My mother in law had to get a new unit for her condo. The company had to figure out how to get the old one out and the new one in.

@@HobbyOrganist "Yeah I cant fathom the logic of people putting these appliances in ATTICS" - they have no basement, and likely no crawl space: They're in new orleans.

@@DavidMcKendrick-lives-here Time to put something in that's better accessible than up in a HOT attic

No. The drop in humidity would equalize across the interior. If in a sprawling house layout, the dehumidifier could be sent into a splitter, so it distributes into the pre-existing ducts in different systems simultaneously.

@@Carnie74 that was my question! Thanks

Your biggest concern would be finding a large enough dehu for 4,000 sq ft. Also, a big factor would be just how bad your humidity is in the home, with your current hvac setup. If you’re only at 58-60%, one dehu should be fine. If you’re seeing 65% percent or more, you need your hvac equipment looked at and likely adjusted, and/or adding 2 dehu’s to handle such a large load.

Our house has crawl space as well. Had the energy company (national grid) to send someone to assess the humidity situation and for a 30yr old house, they suggested patching the hairline cracks of the basement walls, spray foam it, the seal the ventilation windows. Then a portable dehumidifier with drain hose is places suspending like in this video does. We no longer have moisture problems. Before that the mold would invade the joists and structural beams supporting the first floor. I do have to remember to vacuum the filter and clean the cobweb at least once every season. Clogged filter means overheated fan motor in the dehumidifier which means fire. The dehumidifier before the mass Gree recall in 2013 and 2014 got overheated and deformed the fan blade cylinder thingy and fused the retractable handle with the unit. Thankfully it did not cause house fire before we replaced it.

I have a question for you. My condensate drains into a pump. unit is located in garage. all well and good during cooling months but how do I prevent air from being pulled up into the condensate drain in the winter when the pump is not full of condensate? a p trap would dry out pretty quickly too so that won't help. A trap primer? or some kind of thin rubber flapper on the bottom of the condensate drain?

You’re talking about a difference of $1500 for a dehu install, to a $15k install for an inverter system. If the system isn’t that old, and is running fine, there’s absolutely nothing wrong with adding a dehu like they did.

"humidifier" - that's your problem :)

These units typically weigh anywhere between 50 and 100 pounds depending on which model you purchase.

Honestly, for a basement you should install a standalone dehumidifier. You can get models that have a small pump in them and will empty automatically.

@@CheezburgerBrown ^^^Yup. Exactly the correct answer.

Im pretty sure you can just tie onto the existing drain.

I would imagine that this is only using the fan to circulate air through the house.

What kind of furnace humidifies by itself? Lol. A furnace acts as a dehumidifier in colder months. Not by design, it’s just how it works. Which is why you’ll need a HUMIDIFIER in colder months, to keep RH around 50%

Nel Edora If it's to prevent mold, then install a bathroom fan to the outside. If it's only to keep the mirror clear, install something behind the mirror to heat the mirror. Something like resistance wire on a small low voltage transformer.

Turn the bathroom fan on, problem solved.

Maybe if you left the bathroom door open while taking a shower. Bathroom fans already exist for that though.

I'll give it a B

Yes

Humidifiers are very ineffecient. When we fire up our portable HiSense unit at home and use it for a few days in the aummer the electric bill jumps easilly 20% or more

@@lakorai2 You're looking at a portable. I've got that too. My bill goes up 40 dollars a month just to dehumidify the basement. But the upstairs dries out too. I imagine a whole house unit is better than the little ones we have.

Probably looking at $2500 or so for everything installed. Which isn’t too bad. Definitely cheaper than upgrading your unit to an inverter system at $15k. If you’ve got the money, spend the 15k on a Bosch inverter heat pump, which will dehumidify very well by itself. But if you don’t wanna spend that kind of money, this set up for roughly $2500 is a great alternative

Humidity in summer time is recommended to be 45-50% RH. So yes, he’s wrong at 35%. They’re not very expensive to run at all. And they’re not even audible other than barely hearing the air come out of the supply registers. Everything in the video was done properly, other than the recommended set point of 35%. Which is dumb. 45-50 in summer. And get a HUMIDIFIER for winter to keep it 50-55% RH.

@@justincoard2591 no 35 is good feels nice.

John Wilson Exactly

That would be putting hot air in your return side, basically bypassing the air conditioner.

No. The air flow from the air handler will take the path of least resistance, which is out of the registers, and will not affect the output of the dehumidifier. Also, ducting the dehumidifier output into the return air side, will cause the drier air to become saturated, and defeat the purpose.

@D B great point! So, how do you feel about installing one of these systems with a fresh air intake duct connected to the whole house dehu? I want to create a positive-pressure environment in my house to reverse the typical negative pressure so I'm not pulling crap from the wall cavities (which I'm certain are moldy to some extent given the humid locale) as well as fresh air that is filtered.

@D B first, thank you for replying. much appreciated. We don't have humidity issues. We would get this to dehu incoming air mostly. otherwise life would be rough with fresh air intake in GA in spring, summer and early fall. re: moisture barrier - it does nothing for what I'm talking about. tyvek stops liquid water from passing through only. convection through drywall into wall cavities causes condensation from the humid air that migrates through the siding. so, what I really need to do eventually is remove all the siding, treat the exterior of the drywall and studs, perhaps spray foam the walls (not really sure what to do there - maybe rigid foam? either way its gonna cost a lot sigh.....) to prevent a wall cavity that is essentially a mold incubator (no UV exposure, plenty of cellulose and water from condensation). I was hoping this would help in the meantime so we aren't so sick. kind of a stop gap measure.

Good question. That would be a great option for a HVAC system.

Yes. The higher end variable speed units do a great job of dehumidifying. But it’s also gonna run you 15-20k to install one of those systems. This is a much cheaper alternative

stay away from whole house humidifiers. first, they die quickly. second, they can encourage mold growth in your ducts etc. Just use portable room units for humidification.

@@coppulor6500 I moved into my home and there was a humidifier unit. It didn't work and was all clogged up. I just didn't use it. My wife uses a humidifier in the bedroom and that's it. I agree, stay away from humidifiers in the household unit.

@@beebob1279 see above replay to JC (jeez, even his initials are JC! lol)

Jesus, I live in Marietta, GA. I have been inspecting homes for 24 years, have perfect reviews on my google business page and on Angie's List and am fully code certified (which is a big deal because very private inspectors are as is not required - in fact, GAHI (Georgia ASsociation of Home Inspectors) is the only association of private inspectors of which I am aware, that requires it members to be code certified (that means certified in the IRC (International Residential Code)) the requirements of which must be adhered to by law for new construction AND rehab and additions and newly installed systems such as HVAC etc. I am not bragging just trying to establish the fact that, even though I am smart enough to know that I don't know everything, I feel comfortable calling myself an expert. So, please consider the following info. I tell every one of my clients (just happened yesterday, in fact), to remove whole house humidifiers IMMEDIATELY. They obviously dramatically increase the humidity in your ductwork. This very often results in condensation in your ductwork because some parts of your duct system are colder than others among other reasons (including leaky ductwork etc blah blah blah). I don't want to go into too much detail (I have a report to write but I couldnt help taking the time to reply because of the importance of this issue to one's health and Bea Bob's comment made me look at my inadequate previous reply and helping others is a priority for me). I very often find mold in HVAC systems. Particularly heat pumps. I moved into my girlfriend's house several years ago and removed the humidifier immediately due to the symptoms she and her kids (and I) where experiencing. That lead to further investigation of the ductwork (including removing some of it to look inside and take photos etc). I show these pics to my clients often and they gasp, their mouths are agape and the look on their faces is one of disgust. We have humidifiers in our rooms. The steam kind (the other kind can create mold in the filters). We have dehumidifiers in our garage, basement, and upstairs hall - a whole house dehu would be great but we'll do that down the road when have the money for that and an ERV for fresh air exchange (we want a ventilating whole house dehumidifier). Yes, I know it gets much much colder in North GA and constant heating dries everything and everyone out, but trust me, its worth the hassle of refilling the ones in our rooms vs worrying about mold growth in our HVAC system and house (as mold in ductwork obviously releases mold spores and, worse, mycotoxins - all of which are then wonderfully spread throughout your house. Almost nobody understand how unbelievably toxic mold is to your brain. Mycotoxins can pass through the blood/brain barrier and ruin your life - everything from depression to Alzheimer's to almost unstoppable lung infections to death. Do yourself a favor and read this article. paradigmchange.me/wp/fire/ two more things. mold spores are EXTREMELY small. 10,000 spores can fit on the head of a pin. you cannot eliminate them from your environment but you CAN make sure your house is not a place mold can grow. lastly, if you have questions or want to see some photos, feel free to gimme a call. I am not trying to advertise since I am always overflowing with work (which is why I no longer have an actual website). do a search for HI-Tech Home Inspections 30066 and you will find my business listing and contact info. I'd be happy to help you for free (just keep it reasonable lol). Best of luck!

@@coppulor6500 Thanks for the information. I was told this when the heat pump was replaced years ago. I never put in a new humidifier. I just might end up having the duct work checked anyway for mold.

They're in the South. Humidity can be 80% on cool fall and spring days here

Totally insulated attics should have at least one A/C supply in them to take care of humidity. House moisture will work it's way up there.

Depends on time of year 60 is very high 50 or lower.

LOL!!!!

Just put a switch in-line with the AC unit's fan, controlled by a humidistat. Easy! 😋

Yeah pretty much .. I did new construction ac systems in Houston tx and if you build with foam insulation code requires you either have 2 stage system or dehumidifier

Maybe they should have installed an automatic venting system with heat recovery instead of a dehumidifier.

“In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. If the air distribution is in the attic space, then consider insulating the rafters to move the distribution into the conditioned space.” www.energy.gov/energysaver/weatherize/insulation/where-insulate-home

Humidity rises typically. Ultimately it shouldn't matter, the humidity in the air will equalize through the house assuming your house is tight enough and more humid air isn't coming from outside than the dehumidifier can handle.

so they used something called mastic, its like a pasty thick glue that sticks it together. its a better seal than a zip tie...I wish they used both though.

Ron White correct the tape that was used wasn't even duct tape. However I have serviced many Ac units without zip ties and have found duct tape only gets stronger with time. Undoing an old joint is like chipping up concrete.

Not duct take. It’s metal foil tape. Looks the same but its not.