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Air pressure result of leaving unrestricted daylight drain pipes (radon related)

ylekyote | Posted in Energy Efficiency and Durability on

I had a post on here about a similar question but can’t find it. Anyways, I am considering leaving two 3″ PVC drain pipes in my crawl space (CS) and walkout basement open, as-is. Instead of putting one-way valves on them to restrict outside air suction.

Reason, I wanted to experiment with Radon mitigation and household air pressures and draft. I have high radon levels. I want to see if a passive system (as in sealing dirt CS) will work good enough, or at least rule the greener way out. I’ve sealed my dirt crawl space area with vent plugs, sealed doors, and two layers 6mil plastic over some scrap plastic foam sheets I salvaged from a friend. I placed a few feet of 3″ radon PVC in the CS if a fan is later required to bring radon down further, by fan exhausting the dirt-side air to the outside (active system).

The two 3″ PVC water drains are from appliances (washer, water heater, solar tank, cistern overflow, etc). I can’t close them entirely, but water rarely sees them. There aren’t any traps or one-way valves on them presently either, so they seem to presently suck fresh air into the house with a stack effect.

I have one 6″ wood stove chimney pipe I plan to leave functional for winter heat. I also have 2 standard bathroom exhaust fans that are seldomly used. In summer we use natural air to cool house during evenings and then trap it inside during the day and close as many curtains as possible to block UV heat. So the home is open to the air at night and closed up during the days of warmth.

1. If I leave the open drain pipes as-is, won’t the effect be that my house will create a stack suction (summer and winter) and should draw fresh air from my daylight vent pipes (that are in far yard) into the house via the floor drains?

2. If the crawl space is sealed tight from outside and good enough (no perceivable gaps) from the inside living area above, what will that do for the air in the crawl space? Should this configuration make a slightly positive pressure on the CS so the air will, if anything, mostly stay down in the CS or slowly leak to the outside? Or will my idea continue sucking air from the crawlspace in addition to the daylight drain pipes?

I don’t understand the science of household air pressures, obviously. Thanks!

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  1. Expert Member

    I can't comment on the effect of the drains on the house pressure but I don't think using drains as fresh air intakes is a good idea.

  2. ylekyote | | #2

    Why's that? I wouldn't if pipes were dirty, or if I lived in a really wet/moldy climate, but it's dry here in western CO. Based on my bag I taped over the interior CS door, when I sealed everything it seems to not be pushing air from the CS to the house above a section of it. So maybe my pressures are negative in CS now, or neutral with rest of house? It's not sucking down to the cracked CS door either. It's just loose. Before CS sealed it ballooned upward as if air was coming strongly from CS into main home.

  3. Expert Member

    Code issues aside, I don't think there is any climate I'd be comfortable allowing an air intake to travel underground before entering a house. Even assuming the outlet precluded the pests usually deterred by traps or valves, I don't think I would characterize such a pipe as clean. Especially one which, even occasionally was used as a drain.
    What you are proposing is similar to an earth tube. There has been some discussion around this on GBA in the past:

  4. GBA Editor
    Martin Holladay | | #4

    Where are these open drains (on the house side)? Are the drains in your crawl space? Or are the drains in your laundry room or mechanical room, above your crawl space?

    In other words, where do these pipes introduce outdoor air? Are the pipes introducing outdoor air into your crawl space, or introducing outdoor air into a room above your crawl space?

    If you think that a big hole in your house will provide ventilation "summer and winter," you're only half right. The ventilation rate will be all over the map -- from almost no ventilation (on spring and autumn days without wind) to irritatingly enormous amounts of ventilation (in the winter, when the stack effect is strong and the wind is blowing).

  5. ylekyote | | #5

    Hello. The two 3" dia drains exit ends are in my yard, slightly lower elevation than where they originate in the house. They originate in the walkout basement and first level of home, from the laundry room, cistern room, and mechanical room. There are 3 or 4 origination points in the house, that appear to be 1.5" to 2" pipe diameters. At some point under the house CS they increase to the 3" PVC pipe and run into the lower yard.

    My house needs some intake air because I have a wood stove that needs that. So I thought these could supply that as well as keeping a slight positive pressure over the sealed CS.

    The CS is now sealed from the portion of the house above it. Tight enough where no air pushes into the house and floats a plastic bag over my interior CS door in the floor of one of my rooms above it. I cracked this door about 2" and taped a bag over it. Before it would balloon upward from air pressure in the unsealed CS. Now it lays flat as if no air is coming upward from CS.

  6. GBA Editor
    Martin Holladay | | #6

    You discuss three areas in your house: (1) Your basement. (2) Your crawl space. (3) "The first level of my home."

    We don't know how these three areas are connected -- whether these areas are all separate, or whether some are connected. We don't know whether you have tight air barriers between these three zones, or leaky air barriers.

    It sounds like you are now introducing outdoor air into two of these three areas -- the basement and the first floor of your house (presumably, one floor above your basement and crawl space). I have no idea how this outdoor air affects your crawl space, since the outdoor air isn't being introduced there.

    I still think that these open pipes are a bad idea. If you want an energy-efficient house, you need to reduce uncontrolled air leakage into your house.

  7. charlie_sullivan | | #7

    If you are concerned about radon and like to tinker, I'd suggest an electronic radon meter. Then you can make adjustments and see the effect over the ~2 week time it takes to get a reading. You might also want a manometer, so you can see the immediate effect of various changes on the pressure difference between the crawl space and outdoors.

    I can't think of anything that you can do to create positive pressure in the basement when it's colder outside than in, short of an active ventilation system. The stack effect will create negative pressure there. Opening vents to between the basement and the outside will reduce that negative pressure, but won't create positive pressure. Sealing leaks near the top of the house will also decrease the negative pressure in the basement. Sealing leaks near the top of the house is generally better because it will decrease your overall air leakage rather than increasing it.

    If you move to active pressure control, depressurizing the sub-slab area is probably easier and less energy intensive than pressurizing the crawl space.

    Using drains as vents has the problems others have noted, but if you clean out the drains and don't put nasty stuff down them after cleaning, and you are in a dry climate, it might be OK as far as air quality. The air leakage rate might be higher than you want.

  8. ylekyote | | #8

    Yes you're correct. First level is ground level as well as some area over of my CS. Walkout basement is also connected. The first level and walkout basement is all openly connected, free flow air exchange.

    There seems to be numerous designs for the earth tube uses as I just looked. So I guess I'm trying to retrofit some of this theory as well as allow for wood stove intake air and trying to keep my living area from sucking air from the CS.

    My house living areas are pretty tight. And I have double pane windows. It's stucco with metal roof (no attic), not flat but very minimum pitch on roof.

  9. ylekyote | | #9

    Yes I have an electronic radon detector. It takes 48 hrs for initial reading. Seems very accurate, at least as accurate as the charcoal testers I compared results with. It reads 11 in CS. I'm hoping the sealing will passively reduce that to below 4. Will see. If not I'll have the pipes under the plastic to connect it to a pipe on exterior wall and expell more of it to reduce lower. Last resort will be putting a fan on the pipe to vacuum it out.

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