Radon suction pipe diameter

[dbooksta]

Oops -- originally posted in Residential HVAC. Since I don't know how much crosstalk there is thought I'd repost here to see if I get any other opinions:

I'm putting in a sub-slab suction system for basement radon control, and my question is whether pipe diameter or impedence should be a concern?

My guess is that it doesn't matter how small the pipe is or how many bends and runs it has simply because there should be very little sub-slab airflow.

The suction fan maintains 1.75" static pressure with no airflow. Key assumption is that once it is running the entire pipe system (no matter how convoluted) and sub-slab pits will be depressurized and pretty much stay that way unless there's a significant leak into the system.

I.e., my assumption is that when properly sealed the system will not have high subslab airflow. (After all, how much air can you suck from clay shale under a foundation.) And I am reasoning that with very subcapacity flow rates I can seriously downsize, twist, and turn the pipes without preventing that little gas from reaching the exit point.

Is there anything wrong with this reasoning?

[teddy bear]

Depends on the length of the suction line and air leakage from basement. Short small system could be 4". Double pick-ups and +40ft of pipe should be 6". My EPA certification is 15 years out of date. You need professional help. Test for adequate radon mitigation after job complete. TB

[Xavier]

I think "Oops" is the answer. Why are you installing an expensive system that cannot adjust for any changes in Delta P in the home, when opening a window will reduce/eliminate Radon in your home?

[teddy bear]

Originally posted by Xavier
I think "Oops" is the answer. Why are you installing an expensive system that cannot adjust for any changes in Delta P in the home, when opening a window will reduce/eliminate Radon in your home?
Good radon mitigation generates well over a 1" of suction under the slab. That level of pressure is not effected by a window or exhaust fan. It may be effected by a 40 mph wind but little less in a home. TB

[dbooksta]

Yeah, in fact I already tried an active/forced ventilation system to mitigate the radon. I'm using a Thermastor FilterVent to pull 75cfm of outside air into my air handler. I was hoping I could both refresh the air and keep a positive pressure to reduce radon infiltration. That did reduce my radon levels from 10-12pC/L to 8-10. But its efficiency varies by season because during extreme weather I can only run it when the air conditioning or heating is running.

I might have better results with a true air exchanger running higher volumes, but the problem with radon is that no matter how much you change the air you'll still have infiltration from the subsoil unless you can keep strong positive pressure in the house. My house isn't very tight, and there's the natural "chimney" effect working against the pressure too.

Subslab suction seems to be the canonical solution to prevent infiltration. It'll just be a lot easier for me to run 1" pipe than 4" pipe around my basement....

[teddy bear]

Originally posted by dbooksta
Yeah, in fact I already tried an active/forced ventilation system to mitigate the radon. I'm using a Thermastor FilterVent to pull 75cfm of outside air into my air handler. I was hoping I could both refresh the air and keep a positive pressure to reduce radon infiltration. That did reduce my radon levels from 10-12pC/L to 8-10. But its efficiency varies by season because during extreme weather I can only run it when the air conditioning or heating is running.

I might have better results with a true air exchanger running higher volumes, but the problem with radon is that no matter how much you change the air you'll still have infiltration from the subsoil unless you can keep strong positive pressure in the house. My house isn't very tight, and there's the natural "chimney" effect working against the pressure too.

Subslab suction seems to be the canonical solution to prevent infiltration. It'll just be a lot easier for me to run 1" pipe than 4" pipe around my basement....
I have had limited succes with filter-vent but used it differently. Suggest connecting upstairs air to 8" duct/6"fresh air discharging total into the basement trying to pressurize the basement. You need a good seal on the basement door and seal all cracks to upstairs and rim joist to outside. Try and test during the summer. TB

[dbooksta]

That was the idea I originally had in mind, but unfortunately I have a finished basement with no door to the first floor. (Also, I'm in PA so during the summer I would end up with major condensation/humidity problems in the cool basement if it weren't forced through the central A/C first.)

[cem-bsee]

so, seal all boxes to wall -- with spackling or caulk or foam
caulk around all of the trim, including above & below baseboards --
seal all HVAC ducts & boxes with mastic at seams & joints & corners
caulk all wall junctions -- corners, to ceilings

run the 1" pipes into a 4" manifold, often