Misconception: Should I Close Crawl Space Vents in Winter and Open in Summer

Crawl Space Misconception Series - If you have a vented or open crawl space you may be planning to seal your vents in winter and open them in the summer. Here is some advice on why crawl space encapsulation may be a better choice.
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[@tracywoolery5066]

I can listen to this stuff all day long.

[@sergii_contractor]

Haha me too!

[@diamondbracelette]

Great vid. I'm in a flood zone in the NE and have opted to not encapsulate. I don't believe it would to code even if I wanted to. We've recently replaced some insulation under the subfloor (in the crawl space) with mineral wool, and I'm wondering what the best options to reduce summer humidity and moisture might be, where the vents will remain open. A vapor barrier on the ground is definitely on the list.

[@CrawlSpaceNinja]

Great Question! There are still other steps to lowering humidity based on your situation but the crawl space dehumidifier is the most important piece of the puzzle. By installing a proper vapor barrier and sealing doors and vents, it allows the dehumidifier to do its job more effectively. This will save you money in the long run because the crawl space dehumidifier is able to reach optimal humidity levels quicker. If your crawl space is flooding or you have a plumbing leak, fixing these items should be part of the controlling humidity process. The crawl space dehumidifier will have to fight standing water or wood that is constantly wet and could lose the battle if the water is too much for it to handle. The Ninja Crawl Space Encapsulation System looks at the entire crawl space from the top down to identify all the moisture problems and correct them. We hope this answers your question. Please feel free to reach out to us should you need some more information. Thanks for watching our video and we hope you have a good weekend!

[@diamondbracelette]

@@CrawlSpaceNinja Thanks! I don't believe my situation allows for total encapsulation due to being in a flood zone where code requires the vents remain OPEN. Part of this is due to crawl spaces such as mine with this type of flood risk, would benefit from water actually getting inside the crawl space to equalize the pressure exerted on the foundation walls. If this weren't the case, encapsulation and humidifier sound like the optimal solution.

[@sergii_contractor]

@@diamondbracelette Ha! Interesting! But how your local code is offering you to get rid of the water built up in the crawlspace through that got there through vents? There are trees and city sewer lines to help to mitigate natural flood water, but what homeowner is left with? To scoop it out?

[@betterthanideserve76]

East Tennessee here, i close my crawspace vents year round, house was built i. 1994. I have a 16mil plastice with 3 inches of pea gravel. During the summer i run a 560 cfm crawspace vent fan with all vents close creating negative pressure down there and pulling some air from the house. In the winter, i disconnect one run of ducting from a floor register and let it warm and dry the crawlspace with dry heat running no vent fan. Crawl space is damn near moisture free year round. No musty smell and radon levels at 2.2

[@CrawlSpaceNinja]

Thanks for your input!

[@cram1nblaze]

Are your supply vents in the floor or ceiling? Mine are in the ceiling and wondering if maybe I need to do something different because of that. My crawl space isn’t insulated, I have vents all the way around the house and two whirlybirds on the roof, I still get wafts of stale air. Trying to remedy that this year. I’m in middle Tennessee

[@BigJack1]

I have recently discovered your channel and watched many videos. In central SC and a new construction going on, we have had a bad mold problem start on wet lumber and plywood. I understand all your steps to improving crawl space air quality, with exception to ventilation after sealing all vents and installing a DEHU in the area. Could you explain how you ventilate or reference a video? Thanks -Robert

[@marcinzemla6265]

Hey Robert i live in Cateechee in Central sc, this guys on point.

[@CrawlSpaceNinja]

Big Jack: Michael actually wrote a blog post on this very topic. This should help answer your question: crawlspaceninja.com/blog/vent-fan/#:~:text=Crawl%20Space%20Encapsulation%20EPA%20Guidelines&text=The%20EPA%20says%20to%20install,square%20feet%20of%20crawl%20space. We appreciate you watching. Have a happy and blessed day.

[@BigJack1]

@@CrawlSpaceNinja thanks so much.

[@SegaCDUniverse]

Good morning Michael. Quick question. Recently we had an addition installed on our home over a crawl with a rat slab, the plans call for vents you can close and one access point outside. For some reason the contractor covered the access point with a fixed window, I was under the impression this would be a window I could access. Anyhow, what kind of exterior access door do you recommend to replace it with that I can also cover properly during winter? Thank you

[@CrawlSpaceNinja]

SegaCDUniverse - great question! We talked to our Production Ninjas about your questions. Unfortunately, we couldn't come up with a solid recommendation for you. In terms of crawl space doors, Lowes is probably the first place that comes to mind. There is, however, no shortage of reliable suppliers where you can buy the access door, but you should consider at least a few things in order to choose the right one. As soon as you decide your budget, you must decide whether to cover the crawl space door from the exterior or from the interior. A weather-resistant exterior door should be chosen if you plan on installing it outdoors. If you fail to select the right one, you can experience problems with the door very quickly. In contrast, you can choose an all-purpose material for interior access doors. A crawl space door can be made of plastic, aluminum, or metal. Sorry that we couldn't be of more help.

[@ryanf.7933]

👍👍

[@bch5513]

Thanks for the video. I live in middle Arkansas and just bought a house with a Crawlspace. No anything except for open vents. Had dry rot I had to deal with in one section. That is done but looking at what to do next . Contractor is telling me just a ground vapor barrier helps a lot and just do that... is there any benefit to just a ground barrier and not addressing the other components? Have brick around Crawlspace and some ancient vents. Some function to close and some are wide open. Also, how much energy savings (%) do you normally get if you go all in on the Crawlspace? Trying to justify cost wise... I am weighing all options now. I've looked at ground vapor barrier, home dehumidifiers, auto vents, vent fans with hygrometers, etc. not sure what to do.

[@CrawlSpaceNinja]

A vapor barrier will help reduce the amount of humidity getting into the crawl space from the ground, but sealing the vents and installing a dehumidifier is the only way to control humidity year round unless your area has low humidity outside. Here is a video we recently did talking about energy savings: kzbin.info/www/bejne/gIvJnKaQj8eljZI

[@jacobbonomo4910]

I don't have 20 grand to encapsulate a crawlspace. I live in Indiana sometimes gets often humid should I just leave vents closed all year

[@omniskorehd4633]

Do you have a video that discusses the specific kind of insulation to use under the subfloor? I heard one home inspector recommend against batt & roll insulation because it retains moisture and acts as a home for critters, but I didn't hear him mention a substitute.

[@CrawlSpaceNinja]

Sub-floor insulation: kzbin.info/www/bejne/b4DNm42tns5jp9k

[@RobertGammie]

Don’t do it. Waste of money. The batts really don’t help and spraying over you wood you’ll never be able to see it’s condition.

[@karensardella7541]

Question: encapsulate or don't encapsulate for a NJ flood zone coastal home with rock/stone in a 5ft high crawl space? We almost always have ground water. We received two totally different estimates 20,000 to 30,000, one covering the vents and encapsulation and one insulating the ceiling and opening the vents. Crazy

[@CrawlSpaceNinja]

Have you seen this video I did with Crawl Space Ninja of Wilmington, NC. They are right on the coast and deal with flood issues and flood insurance. This may help. Also speak to your insurance agent to ensure you don't do anything that could void your coverage. Thanks for watching. kzbin.info/www/bejne/Znm4YmehfduCqNU

[@ValConB]

Out here in the dry west in northern Utah, vents always open in summer, closed in winter but I open them in winter when water gets in due to snowmelt flooding.

[@CrawlSpaceNinja]

Thanks for sharing and watching.

[@ogram46]

I have one-year old residential construction in South Carolina’s Upstate. I had the contractor build a half basement (1k sq ft) and treat the other half like a crawl space. It’s not encapsulated. I received my CO in July 2022. There were no odors upon moving in. Ever since my daughter in-law shut all of the air vents in May or June of 2023. Now, in July, 2023, both sides under the house stink like an enclosed musty failure. In fact, some spare furnishings stored in the basement side had a bit of mold. So, I obviously have moisture problems. The contractor doesn’t back his work. I just want to remedy this problem before it ruins everything. I listened to you advising to pull down the bar insulation. I can do that. If I don’t find a specific area with leakage or mold. What can I do? It smells bad enough during this hot summer, I don’t know what to do. I chose a bad contractor. I have had nothing but problems with this house. My husband has Alzheimer’s and I have lost a lot of tribal knowledge. Four years ago, he would have solved the issue. Please advise.

[@CrawlSpaceNinja]

It is possible there is a thin layer of Mold covering all of the floor and joists if the crawl space is humid. It would be difficult to know for sure without doing some form of mold testing, but if you were near our service area, we would recommend treating the entire subfloor from mold just to be sure. Prior to that, we would need to dry out the crawl space and the wood and make sure to address any flooding if there is any.

[@ogram46]

I will check if there is mold in the areas you mentioned. I’m not sure of your service area, I am located in Six Mile, SC - North of Clemson University. Another possibility is that the ground has settled and I am not satisfied the rain water isn’t properly draining away from my house. I will respond with answers to your question tomorrow. Thanks.

[@CrawlSpaceNinja]

@@ogram46 Sounds great, we do have a branch in Colombia SC if you want to look them up. crawlspaceninja.com/south-carolina/columbia-sc/

[@mercurad]

Hey there. The code IRC R408.3 says you could have an crawlspace vent exhaust fan OR have a HVAC supply line feed into the crawlspace and also have a return vent into the living space. If the whole point of this is because there could be dangerous soil gases that could build up in the crawlspace and enter the living area, how would the HVAC solution help this? It doesn't vent the crawlspace air outside at all in this scenario. So is it really about soil gases?

[@CrawlSpaceNinja]

There is alot to go into this and break down. Feel free to submit a Ask a Ninja form - crawlspaceninja.com/ask-a-ninja/

[@RobertGammie]

Build your house on a slab. Creates other potential issues but worth it imo. What goes on in a crawl space is a never ending pain. Like, I don’t even want to know. Moisture, dry rot, freezing pipes, vent, don’t vent. I’ll opt for a jackhammer over all that crap. If a site is well prepped for a slab

[@CrawlSpaceNinja]

My neighbor had to have her slab removed/replaced due to a plumbing issue. I think all foundations have their unique problems/benefits. We have had to waterproof outside slab homes too. Thanks for your feedback.

[@sergii_contractor]

In cold climates slab is not the best foundation option. Also in flood zones not everyone wants to have house on piers as it will require you to climb staircase every single time, which will be hard task for seniors or if you have kids, so people built on 2ft crawlspaces.

[@Youngbl33zy]

I would never build or buy a slab house.

[@ya472]

Between 2:00 and 2:13, perhaps you can expand on what you said, because it does not compute for me. "part of the HVAC might be in the crawl space or in the attic..." ?

[@CrawlSpaceNinja]

Oh, my apologies. I am referring to the unit itself. Some homes have a package unit where air handler, heat coils and AC are 1 and they are located outside. While other units may have air handler/heat coils in attic, crawl space, basement and AC part is outside. Hope that helps and sorry for the confusion. Here is a link that shows difference. www.petro.com/resource-center/hvac-packaged-unit-vs-split-system

[@ya472]

@@CrawlSpaceNinja Thank you for the link. Many options for the layman to consider. We asked for a 'professional' (well known local company's owner) to suggest a system for our place and give us a quote. No response in over a month.

[@rohoonpark8302]

We recently purchased a split level home with the 3 foot crawl space only under our small living room and kitchen and the floors are freezing cold in the winter. Do you recommend new flooring/subfloor or insulating the crawl space?

[@CrawlSpaceNinja]

Insulating the subfloor in the crawl space is known to solve that issue!

[@mellykick213]

Im lost on this topic. Moved into a brick home built in 2013. Has a crawlspace with the green board insulatation on the walls. Its very dry down there not musty. Ive never owned a home with a crawlslace so i dont know weather to leave the vents sealed or ooen them? When it rains i worry about rain getting in and creating a issue.

[@CrawlSpaceNinja]

Sealing them is best so there is no outside elements fighting your dehumidifier. Enemy number one is Humidity. The outside elements all typically raise that.

[@mikeld369]

question - with closing of the vents does this minimize 'fresh air' getting into the crawlspace leading to more 'stagnant' or 'musty' smells? thanks

[@CrawlSpaceNinja]

We recommend 1 fan blowing out out a vent to help prevent this.

[@adamnonnenmacher7774]

You said the best option is encapsulation for those in the south, but how can you encapsulate if you are also allowing the crawlspace to be vented? Isn’t an encapsulated property completely sealed?

[@CrawlSpaceNinja]

Controlling humidity and soil gases are recommended. This may involve encapsulation, humidity control (dehumidifier) and a vent fan or radon mitigation system according to the EPA IndoorAir Plus program.

[@abrahamponce5543]

My house was built in the 30s and doesn’t have any crawlspace vents. I just got a vapor barrier installed, we’ve had a lot of rain lately and I don’t see any standing water. Humidity levels are in 70s Im almost certain they were probably higher before the vapor barrier. What’s the best solution to this?

[@CrawlSpaceNinja]

Most likely installing a dehumidifier will help.

[@stangssoftwash]

What would you say about encapsulating without a dehumidifier?

[@CrawlSpaceNinja]

Hey there, here is a video we did on that exact topic! kzbin.info/www/bejne/qWSYimWhqbp7mM0

[@premier9710]

im in mb canada, i have mobile home with an addition. recently bought been finding rotten wood, ants i assume or mites ripping the osb sheathing. im replacing all damaged wood and skirting. we have all seasons. the belly wrap is half removed i plan remove all exposing all plumbing vents etc and insulate floor with rock-wool if i can afford or fiberglass. 4 inch rigid foam insulation for skirting, treated wood at bottom for framing inch or two above grading with 12inch rodent aluminum metal block going 8inch below grade or more, metal exterior with vapor barrier covering ground under home then going up skirting to sub-floor, i plan put rock-wool in rim joist cavity. would this be sufficient enough and not have worry about moisture issues? would i need any sort of air exchange or humidity control? half the ground under mobile home wasn't vapor barrier which i assume once done will get rid the earthy/musty smell along with keeping moisture levels down. around previous skirting which was 3-6 inches in ground was complete rotten. appreciate the videos helps a lot thanks

[@CrawlSpaceNinja]

I would recommend you check the humidity in the crawl space. If it is humid, then you may need moisture control. I have not seen subfloor insulation or belly wrap be effective at stopping all moisture.

[@1gesteban]

I'm not an expert in crawl spaces, but wouldn't having the vents closed (at least most of them) help retain some of the heat from the inside of the home? I, too, have said vents and have all but two closed on a one-level, 3100 sq ft home in the Boise, Idaho area.

[@CrawlSpaceNinja]

Having all but one sealed is typically the way to go. Having one vent open but within a foundation vent fan installed to blow the stagnant air can solve that issue

[@michellekotulski9567]

I have watched several of your videos since we purchased a home with a crawlspace. We are in Virginia and our crawlspace humidity was at 80%. We have a vapor barrier down (not full encapsulated), and we called a company to install a dehumidifier. They have sealed (with foam board) all our vents. The humidity is now 37-40% so a big difference. Do we need a fan or something for "ventilation"? It's not real clear. We did test for radon when we bought and we were below remediation level, but I am now wondering if we should re-test. Was this done properly? Should they have added a fan to one of the vents to circulate air? Thanks!

[@CrawlSpaceNinja]

Hey Michelle, glad to hear the dehumidifier is doing its job! We recommend having a small amount of ventilation in the crawl space to help prevent any soil gases from being built up after the vents are sealed. The EPA recommends 1 CFM per 50/sq' of crawl space for ventilation. Here is a video that goes into more detail: kzbin.info/www/bejne/Y2m0kJ2NqreAp9k Hope this helps!

[@grgryl]

I see a vent under my house but we have a concrete slab and no crawl space. Is this vent a for ventilation?

[@CrawlSpaceNinja]

Seems like we would need more information and pictures. Please submit those at crawlspaceninja.com/ask-a-ninja/

[@The1saturn]

with the high cost of electric that I pay the very last thing I need is a dehumidifier running 24/7 365 days a year, and yea I know you can give me like 10 good reasons why I should put one in and I can give you one very good reason why not my end of the month bill

[@CrawlSpaceNinja]

One good reason is that the dehumidifier should never be running 24/7 365. If it is something is wrong and causing that issue. Also if the dehumidifier is set to the proper humidity level such as 45%-50%. It will turn itself off once it is down to that level! Feel free to reach out to our DIY Specialist for more insight and deals - [e-mail]

[@pinkflower22]

My house is on a crawl space and we have a wood heater for heat and no air what do you suggest

[@CrawlSpaceNinja]

Control humidity as best you can. We use dehumidifiers.

[@MrJasonworkman]

Thanks, but how do I encapsulate my crawlspace when I have a radon extraction system in there?

[@CrawlSpaceNinja]

The current vapor barrier may need to be replaced in order to do it properly. Have you contacted the company that did the radon system? If not, I'd recommend you follow their advice so you don't void their warranty.

[@MrJasonworkman]

@@CrawlSpaceNinja ok thanks

[@MrJasonworkman]

@@CrawlSpaceNinja Thanks, but shouldn’t the radon extraction hoses be drawing fresh air from the outside rather than air that you have already heated from inside your house?

[@CrawlSpaceNinja]

@@MrJasonworkman for a crawl space they should be drawing air from under the vapor barrier and pushing it outside.

[@MrJasonworkman]

@@CrawlSpaceNinja Thanks, but where does the air under the vapor barrier come from, surely the ground cannot produce enough air to keep up with the radon exhaust fan?

[@mrjoehimself]

Can I use the cool air from my crawl space to help cool my house?

[@PedalsNPetals]

How

[@CrawlSpaceNinja]

Not sure exactly. However feel free to provide more insight and one of our expert Ninjas can assist you! Here is the form - crawlspaceninja.com/ask-a-ninja/

[@aprilburkett2827]

So are you basically saying keep all vents (except one) to crawl space closed all year round?

[@CrawlSpaceNinja]

Yes!

[@aaronthenorm5400]

I have automatic vents

[@sergii_contractor]

I guess that's the future for some climates, open vents and shut off dehumidifier at certain months with favorable weather conditions to air ventilate crawlspace.

[@CrawlSpaceNinja]

Those can be great!

[@PedalsNPetals]

Ive never paid much attention unless i realized the mice ate through the metal mesh and up to my subfloor and made way into house 😮😮

[@CrawlSpaceNinja]

Lol. Thanks for sharing.

[@rosebraley8628]

Can you explain it in more simple way I have no idea what is a hvac is

[@CrawlSpaceNinja]

Hi Rose, an HVAC system is what heats and cools your home and keeps your living space at the temperature you set it to.

[@jeffflowers729]

encapsulate it and ventilate it. Seems like insulating your walls then leaving the windows open.

[@CrawlSpaceNinja]

I know but its not...got to get soil gasses out or they will go up into your living space. only small cfm of air. Of course, you don't have to ventilate that's just our recommendation.

[@MrNetnut]

Vents Open Year Around. Dirt Covered With Trap. No Insulation . Look great. Memphis Tn ;-)))

[@CrawlSpaceNinja]

Thanks for sharing and watching.