Controlling crawl space humidity

[ERD50]

That's some great research there samclem. I have not read thru the links yet, but I like the idea of the two 4x10 registers. Good point on wanting a return, so the conditioned air does not all go to waste - but I wonder if sizing the return a little smaller than the sources might be good, just to provide a very slight positive pressure, just enough to keep outside, hot humid air flowing in?

Hmm, I'm thinking I might hook up a manometer so I can see that I create a very slight positive pressure for my basement. Would be good to check in winter, to assure no back-draft potential for the furnace (which has a sensor, but best to not have the problem in the first place).


For sheehs1 - consider something like this:

Amazon.com: La Crosse Technology WS-9037U-IT Wireless Forecast Station with Pressure History: Home & Garden

I have a similar unit from LaCrosse that I'm very happy with ( I have three remotes now, outside, porch, and I move the third around to wherever I want to monitor), but my remotes do not report humidity. Put one of those in the crawl, and you can monitor and know that things are as expected w/o having to expose yourself to cobwebs. Plus, since it just takes a glance, you are more likely to actually check it.

-ERD50

 

[samclem]

Good point on wanting a return, so the conditioned air does not all go to waste - but I wonder if sizing the return a little smaller than the sources might be good, just to provide a very slight positive pressure, just enough to keep outside, hot humid air flowing in?

I think the problem is that, barring deliberate forced introduction of outside makeup air, any positive pressure in the basement can only be achieved by producing negative pressure in the rest of the building envelope. If the positive pressure in the basement is keeping moist outside air out, then the negative pressure upstairs is encouraging more of it to come in. And that warm, moist air outside air is going to be sucked into the walls and other places where it will meet the cool back side of gypsum board, etc. And then we get mold.

If we were providing positive pressure to the whole house via a heat recovery ventilator, etc, that would be a different situation.

I think . . .

 

[sheehs1]

I think the problem is that, barring deliberate forced introduction of outside makeup air, any positive pressure in the basement can only be achieved by producing negative pressure in the rest of the building envelope. If the positive pressure in the basement is keeping moist outside air out, then the negative pressure upstairs is encouraging more of it to come in. And that warm, moist air outside air is going to be sucked into the walls and other places where it will meet the cool back side of gypsum board, etc. And then we get mold.

If we were providing positive pressure to the whole house via a heat recovery ventilator, etc, that would be a different situation.

I think . . .

I get this. Makes sense SamClem. I've printed off your link and your long response regarding the other points......and will go thru both.

You are right...if a return is not provided then the crawl space air will just come into the house anyway. They say they have never used a return but I'm going to copy this paper and as you said, reference it when I talk with the HVAC people

They've agreed to spray the entire crawl with Microban 2 days prior to the start of the project. and since we are going into cooler months it should be dryer when the actual work is performed.

THe old HVAC company has agree to come and take out the HVAC system they left under my house at no charge....but can not tell me when. Don't want to start the project until that is out.

I've asked each company (three of them) and they tell me we don't have a radon problem here. ummm.... Think I will call the building inspectors office and asked them that question.

I'll post again once I get thru the paper . Much appreciated SamClem!

 

[sheehs1]

Read everything SamClem. Method D page 4, the supply/return option seems to make the most sense.
Wonder why...not one contractor company I've spoken with seems to do it this way and two of them wanted to encapsulate and put in dehumidifiers.
Have forwarded to the main contractor and asked if he could or would do it as Method D shows.

Found this link for the EPA on national Radon levels for anyone reading this thread that may be interested.

EPA Map of Radon Zones | Radon | US EPA

My question regarding this is while radon is low in my area, does encapsulating the crawl space create a situation where it will build up.? Building inspector hasn't returned my call yet.

My twin sister and husband put a radon monitor in their crawl space but live slightly west of Richmond Va. where radon levels are high.

 

[samclem]

My question regarding this is while radon is low in my area, does encapsulating the crawl space create a situation where it will build up.? Building inspector hasn't returned my call yet.

It is risky to make a determination about your own home's radon levels based on what's happening in the neighborhood. While there are patterns, every house is different. If I were in your shoes, I might buy a radon test kit, put it in my crawlspace now (with no plastic, etc) and keep all the vents closed. Wait the required time (3 days?) then send it off for a reading. It's quite likely the radon levels will be elevated, and if they are, I'd put in the pipes before putting the plastic down. If the radon levels weren't elevated, I'd feel relatively sure that there wouldn't be a problem after installation of the plastic. After the job was done I'd test again: if radon levels were high I'd be happy that I'd laid the pipes in the ground and I'd get a radon remediation guy out or put in the flue and fan myself (if allowed by local code, yada yada).

Truthfully, putting in the pipes and gravel will be relatively easy and good insurance in case you ever do have radon problems. OTOH, if you want to take your chances, installing them later would just mean cutting the plastic, laying the pipes and gravel, and laying/taping new plastic down on top of the pipes/gravel. It wouldn't be hard (compared to jackhammering a slab, etc) and you don't have to do it now if you don't want to.

 

[ERD50]

I think the problem is that, barring deliberate forced introduction of outside makeup air, any positive pressure in the basement can only be achieved by producing negative pressure in the rest of the building envelope. If the positive pressure in the basement is keeping moist outside air out, then the negative pressure upstairs is encouraging more of it to come in. And that warm, moist air outside air is going to be sucked into the walls and other places where it will meet the cool back side of gypsum board, etc. And then we get mold.

If we were providing positive pressure to the whole house via a heat recovery ventilator, etc, that would be a different situation.

I think . . .

And I think... that you are correct.

My problem was that I was thinking of the crawl space in isolation. It is part of the whole house system, as your analysis points out. That air has to be made up somewhere, and if we pressurize the crawl it will be made up through leaks on the upper floors. That said, pulling in a small amount of air into the house ought to be 'less bad' than pulling it into the crawl. Since we probably can't control this precisely, I think I'd prefer to err on the side of a very slight pressurization to the crawl - some vents between the crawl and the house would help equalize this so that we are not blowing large amounts of air out the crawl (which might be part of the links you provided, have not read them yet).

I have no idea if a manometer is sensitive enough to detect these small pressure changes? I see that you can set it at an angle to increase sensitivity. I could experiment easily, and will do it this heating season.

-ERD50

 

[samclem]

I think I'd prefer to err on the side of a very slight pressurization to the crawl - some vents between the crawl and the house would help equalize this so that we are not blowing large amounts of air out the crawl (which might be part of the links you provided, have not read them yet).

Yep, the return air duct description is in the doc at the link. If one wanted the crawlspace to be under slight positive pressure, I think the best way to achieve that would be though direct measurement of pressures like you mentioned and closing off the return ducts from the crawlspace to the rest of the house. Of course, it will only be under positive pressure while the fan is running, which would normally be a small portion of the total time (unless one just keeps the fan running to circulate air, etc).

 

[Tadpole]

This is an old thread but I have a similar crawl space question.

We recently bought a 1958 rancher in Bellingham, WA. I had better insulation put in the attic and had insulation put in the previously uninsulated crawl space. One of my major goals was insulating the heating ducts because by the time heat got to the bedrooms the air was cool.
I noticed after insulating the crawl space that the water was running colder than before. The water pipes were covered with the new insulation but they are not being heated by the lost heat from the heating ducts.

It occurred to me that when the house was built gas was so cheap that people compensated for lost heat in the crawl space by setting the thermostat higher. So it might have been a key element of the design that the heating ducts kept the water pipes warm in the winter.

Have I goofed by having the insulation added to the crawl space? Do I need to run the water during below freezing weather. Can stuffing the vents with insulation during the few below freezing days we have help? Temperatures here usually don't go extremely low.

 

[Dimsumkid]

Tadpole,
Your heating ducts wouldn't be used to heat your water pipes, at least not to any level you'd notice. You may be having other issues at work here, have you checked your water temp using an instant read thermometer? Is the heat set to 120 degrees? Is your water heater really old? If you're concerned about freezing pipes, all you need to do is open the basement sink to a slow trickle to prevent the water pipes from freezing.

 

[ERD50]

Have I goofed by having the insulation added to the crawl space? Do I need to run the water during below freezing weather. Can stuffing the vents with insulation during the few below freezing days we have help? Temperatures here usually don't go extremely low.

Put a remote, wireless thermometer down near the pipes. You can monitor it and see. It would take some significant time for the water to freeze if you are occasionally just dipping a bit below 32F . It has to drop the water from supply temps (50-60?), and then it takes 144x the energy to pull that last degree out to go from above freezing to forming ice. Running the water at night and first thing AM would probably be OK.

But if it is below 32F for extended times, you'll want to start getting serious and do something to warm it up, and/or trickle some water.

It makes little difference what the outside temp is - there are so many variables, you need to know the temp where the pipes are. Get the thermometer.

What would stuffing the vents do? IF anything, that would cut the airflow, the ducts would be cooler and there would be less heating of the crawl (unless there are vents to the crawl in those lines, so the air would be driven down there)?

-ERD50

 

[ERD50]

Tadpole,
Your heating ducts wouldn't be used to heat your water pipes, at least not to any level you'd notice.

I'm not so sure. The hot air in the ducts is ~ 100F, and those ducts have a lot of surface area of metal. I think they would give off significant heat. If not, why do they recc insulating them?

edit/add:

It occurred to me that when the house was built gas was so cheap that people compensated for lost heat in the crawl space by setting the thermostat higher.

Just to be technically correct/nit-picky - you don't compensate for lost heat by raising the thermostat. The furnace will just run longer at the same thermostat setting to make up for the lost heat.

-ERD50

 

[Dimsumkid]

I'm not so sure. The hot air in the ducts is ~ 100F, and those ducts have a lot of surface area of metal. I think they would give off significant heat. If not, why do they recc insulating them?
-ERD50

Back when this house was built, I'm sure the main concern was packing all the utility items in the smallest space possible to look tidy vs. energy efficiency.
Typically, the heat cycles on/off only 4-5 times an hour and you can't butt the water pipes next to the air ducts to be a direct energy transfer, especially since there was enough space to insulate both the duct and pipes. I can't see it making that much of a difference to the water temp. Recommendations for insulating ducts and pipes that I know has only been done for the last 25+ years and people still don't do it today.

 

[ERD50]

Back when this house was built, I'm sure the main concern was packing all the utility items in the smallest space possible to look tidy vs. energy efficiency.
Typically, the heat cycles on/off only 4-5 times an hour and you can't butt the water pipes next to the air ducts to be a direct energy transfer, especially since there was enough space to insulate both the duct and pipes. I can't see it making that much of a difference to the water temp. Recommendations for insulating ducts and pipes that I know has only been done for the last 25+ years and people still don't do it today.

I'm not saying it was a specific design consideration. I'm just saying that I would expect un-insulated ducts to give off a fair amount of heat. Maybe enough, depending on a lot of variables (how sealed up the crawl is being a major one), to keep the crawl above freezing in his locale. If historically, it worked, they just kept doing it that way.

Then some young whipper-snapper with modern ideas comes along and insulates the ducts ( that's not how we do it 'round these parts, sonny ) and upsets the old apple cart. Might get frozen pipes. Might not.

A wireless thermometer will tell us more than we can guess from here.

-ERD50

 

[sheehs1]

Not meaning to interrupt Tadpoles post...but I forgot to update everyone with what I did. I have not done anything yet about my crawl space. There are enough technical issues...that I'm a bit apprehensive about creating another problem.

I think I am going to lay 12 mil plastic, overlapped by 2 feet and taped to the sides first. Second, I'm going to put more insulation on the duct work and make sure there are no leaking ducts. I'll start with this first. Thanks to all that helped contribute to this thread.

 

[Keim]

It sounds like you have fairly easy access to the water pipes. Additionally, your area doesn't get extremely cold for long periods. An easy (and cheap!) solution might be to simply wrap the water pipes with electric heat tape. Then simply plug it in when you are worried.

Or you could get fancy and rig it to a thermostat...

 

[Tadpole]

Thanks everyone. I now realize I need to describe the "crawl space". I do not have a basement. The house is a rancher a little smaller than 1200 sq. ft. The house sits about three foot off the ground. The space between the house and the dirt is what I am calling the crawl space. The outside walls between the ground and the house are concrete. The crawl space is well vented (nine vents, 3 on each of 3 sides).

The workers put in a moisture barrier between the ground and the interior of the crawl space (really thick black plastic). They insulated the heating ducts and put insulation at the top of the crawl space next to the floor of the house. The pipes are also covered with this new insulation so they no longer visible.

So what existed before was a crawl space with an old moisture barrier on the ground and no other insulation.The house is small and the area is small with heat ducts around the outer edge. That is why I thought maybe the lost heat we were experiencing was keeping the crawl space a little warmer than it now is.

It looks like we will just need to drip the water inside the house until I can get temperatures and resolve any problem.

Again, thanks for the input.

 

[Keim]

Unless it is significantly (ie below zero) I wouldn't worry about dripping the faucets.

To add on to my previous post, a small space heater might also do the trick. But I don't think you'll have an issue in any of the weather common to your area. he house has been there since the 50s. If there was going to be a problem, it would've popped up by now.

 

[Dimsumkid]

Looked up your avg winter low temps, 35 degrees, but you hit 8 degrees in 1989. Here in Chicago, when it's below 0 degrees for several days or weeks is when they warn us to trickle the water lines in the lowest faucet to be safe. I'm not sure if all your water lines run thru this crawl space, but it may be better if you make some insulated covers for these vents and cover them during the winter months. I think you should check your hot water line temps for the areas that run in and out of the crawl space to see if you're at 120 degrees and any differences you have between them.

Every time I see this topic pop up, it makes me look since installing a new vapor barrier and insulating my crawl space is next on my to do list, I procrastinate since I'm doing it myself! I just added insulation to my hot water lines in the basement after reading your last post.

 

[ERD50]

They insulated the heating ducts and put insulation at the top of the crawl space next to the floor of the house. The pipes are also covered with this new insulation so they no longer visible.

So the pipes are insulated from the crawl space? This means that they will be getting some heat from the floor above. Obviously, not all that much since heat rises, but the insulation will keep them closer to floor temperature than the crawl temperature. I really doubt you will have any issues at all.

Put that remote thermometer near the pipes. That will seal the deal.

I've got this one - it's great, I've got three remotes. Others may be just as good.

http://www.amazon.com/Crosse-Technology-WS-9611U-Wireless-Forecast/dp/B000EM9DG6/ref=pd_sim_hg_2


-ERD50

 

[TromboneAl]

After we'd been in our house awhile I was walking outside and felt warm air coming out of the crawlspace. It turned out one of the ducts had fallen open. Glad I noticed.

 

[Dimsumkid]

I'm well into the cleanup/insulation of my crawl space efforts to remove/reduce the smell and mustiness and thought I'd share what I've done and results so far:

The entry to my crawl space has 2 -24" openings in the cement wall from the basement, only 1 accessible and the other has HVAC ducts and gas pipe running through it. Crawl space is ~18' X 21' with a clay mud floor and has mouse infestation (more than 3 yrs ago), eaten rodent bait bags and an empty rodent poison gas canister with old plastic sheeting eaten through in multiple places. There's duct running through this space, but no vents and a cold water pipe for the garden hose. One of the smaller HVAC trunks was attached only by a couple of roofing nails driven at 45 degrees directly thru them and of course, had fallen off the joists and dropped 3-4" from the ceiling I had to reattach these with the proper bracing. Wearing a filtration respirator, I removed all the nests I found, 4-6 skeletal remains (nothing like removing a mouse skeleton and seeing all the hair laying around the carcass) and noticed all the clay was damp/wet only under the plastic sheet, black mold/mildew where it was chewed through. Where the sheet was exposed the clay wasn't wet and along the cement walls it wasn't wet. I removed the plastic sheet and decided to put a small 20pt dehumidifier in the space and set it to 4.5-5 on the dial (what I usually set it for the basement in the summer). My house seems to be sitting on wet/damp ground as my humidity levels always tend to read on the higher end all year long. I haven't needed to use extra humidifiers in the winter yet since I've been here. Temp today is 39 high, 53% humidity. Yesterday low 40's, and humidity 83%. After 1 day, I got about 2" of water collected, 2nd day about 3/4" and the wet top layer from the clay disappeared and the smell reduced dramatically. After raking the clay, and removing all the old rotted wood and debris, I laid down 4 mil plastic sheeting loose with no adhesive and fortunately no cutting, added pipe insulation, sprayed expanding foam around my sill plate gaps (~1") and notches in the wood for the sill plate bolts (up to 2"x2"), only thing between crawl and outside was a layer of roofing felt and brick. I waited 2 days and checked the dehumidifier tank and no water collected, checked under the plastic and it lightly damp, but not wet looking clay!

Also have noticed an increase in the basement temperature (it's unfinished, cement walls), but this may also be due to filling and sealing all the open holes left along the sill plates when this house was built (1963). I have a huge tarp that's thicker than 4 mil to lay on top of the plastic sheeting if needed, 2" rigid foam boards for the exterior walls. I may also insulate the HVAC duct too. I plan on leaving this dehumidifier in the crawl space. I also have many rolls of new plastic sheeting that's 3 mil or less, but not sure if additional layers of plastic will make a difference for me.