Radon vent into existing basement slab
ahneedhelp
| Posted in Construction Techniques on
After reading most of radon related threads, a question has come up.
What are the chances of the basement slab radon vent tube drawing up water from the gravel pit below ?
Has anyone heard of cases where the below slab gravel layer becomes saturated with water and the radon vent tube drawing water up above the slab level ?
For the purpose of radon mitigation, breaking up the slab and digging deeper to add gravel (if for some reason there is not a gravel base) is not a problem.
Just curious if this spot could become the path of least resistance for the groundwater.
(We don’t have any moisture problem in the basement.)
Thanks for any insight.
Replies
I'm guessing that the blower on an active radon system is too weak to pull any significant water.
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Certainly, if the ground water level rises above floor level, the water will come up through the radon vents. But the vent fan only draws about an inch of vacuum, so it's not going to suck the water up.
If you can break up the slab, though, and if groundwater is a problem, the thing to do would be to install a combo tile and radon vent, draining to a sump. In the sump you install a sump pump, then you seal it and install a radon vent fan pulling from the sump. They make special sump seals specifically for this.
If you're unsure if you have a groundwater problem, you can still install the tile and sump, and add the sump pump later if needed. (But be sure that you set it up so that you can later add the drain pipe to daylight/storm sewer for the pump.)
Thank-you for the replies and suggestions.
One more Q....
One corner of the basement is the boiler/utility room.
The boiler will be enclosed with its own outside air supply plumbed in.
This is the northwest corner of the house that is below-grade (below the above-grade rim joist.).
I have seen radon mitigation retrofits that were usually in the corner of basements, so I am looking at installing the vent tube in the soon to be enclosed boiler room.
Is this corner location as effective in creating negative pressure under the slab compared to having a pit dug in the middle of the basement slab ?
And for this negative pressure scheme to work, how much gravel base should I hope to find under the slab when I break it up ?
I can only assume they used a gravel base in the 1950s.
This brick ranch seems to have been custom built by a faculty in the university town we live in.
This whole idea would be changed if I encounter a solid slab of clay underneath.
Seems to me such matters must have cropped up here and there...
Not sure you can count on anything in particular under the slab. Could be gravel, sand, or dirt. Depends on local construction practices, whether there is plumbing below the slab, etc.
If you dig up the slab and put in tile then it doesn't matter where you put the pit. If you don't want to dig up the slab then probably the best choice in one of the "systems" that runs a tube around the outside wall with vent penetrations every 2-3 feet.
(Of course, before you go to the trouble of any of this you should do a radon test. Even if other homes in the neighborhood have radon problems, that doesn't say that yours does -- radon can vary 10x or more in adjacent homes.)
re - If you dig up the slab and put in tile then it doesn't matter where you put the pit. If you don't want to dig up the slab then probably the best choice in one of the "systems" that runs a tube around the outside wall with vent penetrations every 2-3 feet.
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Digging up the slab won't be a problem.
Quite familiar with retrofitting large sump pits, so psychologically it's not such a daunting task (but my wrists may not appreciate it.)
Can you explain "put in tile" ?
I thought the pit would be filled with gravel for the gas to accumulate in and then drawn out via negative pressure created by the fan.
Or is tile another name for loose fill ?
Thanks for the suggestions.
[QUOTE]
Can you explain "put in tile" ?
I thought the pit would be filled with gravel for the gas to accumulate in and then drawn out via negative pressure created by the fan.
Or is tile another name for loose fill ?
I mean that you would put in (plastic) drain tile, draining to the sump. Ideally you'd do the entire perimeter and one down the middle, but probably a couple of legs running about halfway to alternate corners would suffice. Backfill around the tile with gravel or coarse sand.
The 50's house that I am moving plumbing around in appears to have about 2-3" of HARD concrete over big rocks and dirt. Those big rock might have just rough surface of the ground that got filled up with concrete.
But whatever it is there is not clear layer of say 1/2 or 3/4 gravel.
How high are your radon readings?
In my area (NW Ohio) if they're not much above 4, they seal the sump crock cover and run the radon vent from it.
And the Ohio EPA says that adding a radon mitigation system could create neg pressure and efect combustion appliance drafting.
Seems pretty unlikely to me, especially if you're pulling combustion air in from the exterior (Skutle vent?) but it might not hurt to have a draft test done on your boiler after the installation. (Draft should be between 0.01 and 0.02 wcin.)
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Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Bob -
Thanks for the reply.
The two 6" air supply tubes for the future boiler room are sized for the current gas boiler. In the future, one of them will end up becoming the side-wall vent/intake for a more efficient wall hung condencing unit.
As for the radon vent creating backpressure against the boiler, isn't the slab resealed around the vent tube that drops down below into the gravel layer ?
We don't have a need for a sump pit and the approach will not be to use one with a rubber-sealed lid.
The radon vent will be the type that would be sealed up by the slab that is repoured around it.
I could be missing some details so please share more of your thoughts.
>>As for the radon vent creating backpressure against the boiler, isn't the slab resealed around the vent tube that drops down below into the gravel layer ?
>>The radon vent will be the type that would be sealed up by the slab that is repoured around it.
>>I could be missing some details so please share more of your thoughts.
Well, I'm not sure as I agree with the Ohio EPA, but they're the ones who have raised the issue.
And if our basements were perfectly sealed against gas penetration, then we wouldn't have to deal with radon getting into the house in the first place.
The Ohio EPA's thought process seems to be that a radon mitigation system (mit system) lowers the pressure in the basement (which, in most houses, is already a negative pressure zone.)
Combustion appliances have pretty low pressure in the flue, so the OH EPA is concerned that the added negative pressure in the basement from a radon device could lower the pressure enough to cause back drafting.
(I've seen cases were running a bath fan on the second floor can measurably lower flue draft pressures in the basement appliances - rare, but I have seen it.)
Now, in your case, where you're adding make up air supplies for the boiler room, it seems very unlikely that adding a radon mit system will cause any such problem, but I still think it can't hurt to double check.
I don't know how much air mit systems move, but imagine that the air make up supplies you install are just barely adequate to provide sufficient make up air for your appliance, and there is a hidden crack in the floor that allows the mit system to lower pressure ....
Again, a pretty remote likelihood, but perhaps worth at least a few moments thought.
(And I'm assuming that some folks reading this might be finishing basements and not considering combustion air issues.)
And, FWIW, in my area, the mit systems are always installed on the perimeter of the basement, I don't think I've ever seen one in the middle of the basement.
_______________________
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I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Bob -
Thank-you for the cautionary note.
I'm in the middle of Tamoseal'ing two sections of dry but bare block walls. This alone may help, and when the boiler is enclosed in it's own room with fresh air supply, this may reduce the overall negative pressure in the basement created by the boiler when it was breathing off the basement air.
It was determined a while back that the basement air volume (approx 1750 sq/ft) and the older hopper windows in the utility room were drafty enough to adequately supply the boiler combustion air.
After these are finished, a long-term Radon test will be done.
The first reading from the short-term test showed that is was several notches above the safe level, just enough to warrant long-term test.
Thanks again for your thoughts.
FYI - assuming 8 foot ceiling - a 1750 sq foot area would be deemed large enough to provide combustion air for up top 280,000 BTU (assuming no competeing air uses such as dryers, vent fans, etc.) at 50 cu feet per 1,000 btu
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Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Thank you for the figures.
Yes, we have 8' ceilings.
The boiler is rated at 93,900 btu.
There is an electric dryer in the vicinity but rarely do they run at the same time.
Even if they do, I think the basement air volume and minor air infiltration through the windows is enough.
There are no other active venting mechanisms.
My info indicates two 6" supplies will be adequate for the size room that wil be enclosed for the boiler.
Back to mixing and applying more Tamoseal....
Bob, what is the source for the numbers you quote below?
FYI - assuming 8 foot ceiling - a 1750 sq foot area would be deemed large enough to provide combustion air for up top 280,000 BTU (assuming no competeing air uses such as dryers, vent fans, etc.) at 50 cu feet per 1,000 btu
I'm about to begin finishing off a basement that contains both an oil fired furnace and an oil fired water heater. The plan is to enclose them in a seperate room, but I need to figure out how much make up air to bring in.
Thanks, and sorry for the thread hijack.
Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
That's in most codes and is, I believe, based on GAMA (Gas Appliance Manufacturer Assoc) figures.
The gteneral rule for makeup air for combustion in an enclosed space is 1 sq in of _free_ vent space per 1,000 btu, 1/2 high ans 1/2 low in the space. Free vent space ios based on the manufacturer specs for the grills place over the holes.
I've never been able to get a definitive answer of how you calculate it if you have a grill on each side of the hole, but common sense says to me you have to calculate for both:
E.g., 10x12 hole = 120 sq inches. 50% free vent rating for a grill on one side measn 60 sq in; add on another 50% on the other side and it becomes 30 sq in, but that is just a guess.
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Edited 3/9/2004 11:39:47 AM ET by Bob Walker
Look at CodeCheck. The online version shows the table, but some of the info is missing. You need to buy the book for the full details. Also shows some alternate methods of sources for supplying the air.
Thanks Bill and Bob. Code Check? Duh.... I've got the book.
I did find the requirements that Bob listed online, as well. I know what I need to do now so as not to kill my clients.Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
FWIW I was just reading a Cat 1 furnace installation manual (idle hands are the devils workshop {G}) and noticed a couple of things -
For combustion appliance(s) in a confined space (less than 50 cu ft per 1,000 btu) you always need at least 100 sq in of free vent space even if the app is less than 100,000 btu, - IF those vents are communicating with other interior parts of the structure
If combustion air is being brought in from outside
with vertical ducts:
40,000 btu needs 10 sq inches;
60,000 btu needs 15 sq in
80,000 btu needs 20 sq in
100,000 btu needs 25 sq in
120,000 btu needs 30 sq in
140,000 btu needs 35 sq in
Double the vent requirements for horizontal duct.
And there are a bunch of things that require a source of outdoor air - commerical buildings, indoor swimming pools, and exposure to a bunch of chemiclas including: water softening chemicals, cements and glues, anti-static fabric softeners for clothes dryers(!) chorine based chemicals.
And for gas dryers you add in the dryer btu amount, I'm still not sure what to do about elec dryers in the same space as gas appliances, though
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Thanks for the additional info Bob. It fits with what I found on line today. I've got 100,000 btus, horizontal ducts, so I figure that 2 6-in. ducts ought to do it nicely.
How did we ever build anything before the internet?Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.