Anyone have a radon mitigation system in their home?

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Oct 15, 2020
153
New Hampshire
Wife and I are buying a house that’s having a radon mitigation system installed by the sellers.

My concern is we wanted them to also install a large dehumidifier because the basement is quite musty due to some drainage issues around the sides of the foundation and a torn vapor barrier in the crawlspace.

The sellers are claiming that the radon system will reduce the humidity in the basement enough to remove the need for a dehumidifier.
What are your thoughts on this?

Im quite skeptical as I think a lot of the humidity is from the drainage issues around the foundation and pulling air from under the foundation(radon system) isn’t going to be handling where most of the humidity is coming from.

We do plan to install a French drain and possibly gutters in the spring but we don’t want to have to pay another $1100 down the road because they wouldn’t put in the dehumidifier we wanted.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,597
Northern NH
I dont own one but I agree. The radon systems I have seen consist of fans connected under the slab to create a subslab pressure gradient under the slab along with sealing any sump pits and floor cracks. On occasion there may be floor drains going below the slab and they will be equipped with float device to open when water is actively flowing and close the rest of the time. The fans dont pull a lot of air and what air they will be pulling is from the basement so I dont see a lot of dehumidifying effect.

My general observation is radon mitigation pops on many housing transactions (I ran into it selling my parents house). Both parties are in rush and are clueless on how to proceed so the realtor calls a buddy and may get kickback to recommend a firm. Since its no bid situation the markup is usually high.

Depending on your source of hot water, I believe both NH utilities will pay a substantial rebate for heat pump hot water heaters. A side effect of heating hot water is they a dehumidifier (and a need a drain) My guess is that would be lot more effective as a dehumdifier than a radon system.

BTW, gutters can be problem added to a home in a snow zone. NH is in the Ice damming zone and gutters are a major cause. Unless you take them down everyfall and reinstall in the the spring every year you may wish you did not install them. Generally if you insist on gutters the recommendation is to have a couple of strips of ice and water shield under the shingles so when ice damming occurs it doesnt leak into the house.
 

mcdougy

Minister of Fire
Apr 15, 2014
699
ontario
Radon systems are code here in some municipalities. You end up with a fan running 24/7 as you may already know. Essentially here it is drawing the air out of the stone below the basement slab and exhausting it to the outdoors.

Musty smells are usually a sign of mould being present. Is the crawl space a vented space or sealed? Is it insulated or bare walls?
Did anyone look hard for possible mold.
 
Oct 15, 2020
153
New Hampshire
Radon systems are code here in some municipalities. You end up with a fan running 24/7 as you may already know. Essentially here it is drawing the air out of the stone below the basement slab and exhausting it to the outdoors.

Musty smells are usually a sign of mould being present. Is the crawl space a vented space or sealed? Is it insulated or bare walls?
Did anyone look hard for possible mold.

How noticeable is the fan noise? Can it be heard from inside the house or only outside?

Oh the crawlspace vapor barrier was torn and allowed mold. That’s being remediated on the sellers dime as well as a new vapor barrier.

Crawlspace is dirt and the basement is bare cement all around. I’m 95% sure most of the humidity is coming from moisture around the foundation, not under it. So we need to install a French drain when the ground thaws in the spring.
 

mcdougy

Minister of Fire
Apr 15, 2014
699
ontario
How noticeable is the fan noise? Can it be heard from inside the house or only outside?

Oh the crawlspace vapor barrier was torn and allowed mold. That’s being remediated on the sellers dime as well as a new vapor barrier.

Crawlspace is dirt and the basement is bare cement all around. I’m 95% sure most of the humidity is coming from moisture around the foundation, not under it. So we need to install a French drain when the ground thaws in the spring.
Radon as a rule of thumb comes from clay ground only.
Here the fan part of the system is only required after a test is completed and radon is present. The system is an open ended pipe from the middle point of footprint (centre of the house) that is in the stone layer below the slab then an elbow to a vertical pipe that is located near an exterior wall. This is where the the test is performed, a test kit is dropped down the vertical pipe and then the vertical pipe is capped and left for 6 months. When retrieved, if the test shows radon present then the inline fan must be installed and the vertical pipe extended to exhaust to the outdoors.
As far as noisy the house, I would say NO. It's a low velocity fan.
Sealing of all protrusions thru the slab are important (caulk all pipes and pits that come up thru the concrete floor)
If your suspecting a water issue, I would be trying to figure out how often the sump pump runs. Grading is important for sure, but sometimes you may be sitting on a high water table as well. If there is neighbour's close by (subdivision setting) talk to them and see if that's truly the case??
 

peakbagger

Minister of Fire
Jul 11, 2008
6,597
Northern NH
Radon as a rule of thumb comes from clay ground only.

I respectively disagree, its a major issue in NH which is granite. Radon comes out of the granite and we have a lot of it. It can come up through the ground or from well water. A house is inherently lower pressure inside than outside so any radon in the soil gets sucked into basement unless its ventilated. That is not very practical in a cold climate as that ventilation air is cold. The solution is seal up under the slab and pull a suction from under the slab so that the area under the slab is lower pressure than above it. Radon from the ground flows into the lower pressure collection pipes that are drilled through the slab and up through the roof. Radon is heavier than air so the radon in the water from a well tends to come out of the water uses in the house. Gas bubbles get released easier the warmer the water, so sinks and especially showers are going to release radon. Even though radon is a gas, its heavier than air so once it comes out of the water, its tends to flow to the lowest point of the house and build up until ventilated. Since the lowest point of the house is the basement slab radon tends to get sucked through cracks in the floor.Normally its dealt with at the source by air stripping it from the well. Concrete is made with granite aggregate which can give off radon and in some cases the radon in new homes is caused by the concrete foundations.

In areas where there is lot of radon in the underlying rock the house may need a subslab pressurization system and a air stripper on the well. The fans are usually in the basement and are not particularly noisy. They at some point wear out and as they get older the bearings can get noisy which is an indication that its time to swap them out.
 
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Bad LP

Minister of Fire
Nov 28, 2014
1,782
Northern Maine
I respectively disagree, its a major issue in NH which is granite. Radon comes out of the granite and we have a lot of it. It can come up through the ground or from well water. A house is inherently lower pressure inside than outside so any radon in the soil gets sucked into basement unless its ventilated. That is not very practical in a cold climate as that ventilation air is cold. The solution is seal up under the slab and pull a suction from under the slab so that the area under the slab is lower pressure than above it. Radon from the ground flows into the lower pressure collection pipes that are drilled through the slab and up through the roof. Radon is heavier than air so the radon in the water from a well tends to come out of the water uses in the house. Gas bubbles get released easier the warmer the water, so sinks and especially showers are going to release radon. Even though radon is a gas, its heavier than air so once it comes out of the water, its tends to flow to the lowest point of the house and build up until ventilated. Since the lowest point of the house is the basement slab radon tends to get sucked through cracks in the floor.Normally its dealt with at the source by air stripping it from the well. Concrete is made with granite aggregate which can give off radon and in some cases the radon in new homes is caused by the concrete foundations.

In areas where there is lot of radon in the underlying rock the house may need a subslab pressurization system and a air stripper on the well. The fans are usually in the basement and are not particularly noisy. They at some point wear out and as they get older the bearings can get noisy which is an indication that its time to swap them out.

THIS.
 

mcdougy

Minister of Fire
Apr 15, 2014
699
ontario
Here there isn't any granite so my reply was wrong with that fact being withheld. Its basically clay or sand here, and only heavy clay will show a radon positive test. The system im speaking of is placed during new construction, which makes it very simple to place vs a post construction system. We have maps as well that show radon positive areas supplied by the government.
 
Oct 15, 2020
153
New Hampshire
Second mold quote also agreed with me, there needs to be some dehumidifier in the basement after they treat everything. That’s going to maintain the proper humidity in the basement; radon is definitely not going to cover it.

nterestingly enough I was also informed there is a French drain system. I’m wondering if it’s clogged and needs to be cleared out for better functionality. Apparently water does come out of it but I have a feeling it’s not working 100%

The main issue here is....I have no clue where the drain starts. I can only see the exit....

Can’t snake the drain if you don’t know where the start is.
 

Dobish

Minister of Fire
Oct 26, 2015
2,027
Golden CO
I have 3 radon mitigation systems on my property, all going to different places. We had one put in, but the basement was exposed dirt, so they basically put the system under a giant tarp, and tried to seal everything as best they could. This one vents through the foundation and outside. Fan is outside, and I can barely hear a hum running through the system if there is NO noise what so ever. Numbers dropped significantly when the system was installed.

The second is going under the concrete slab in our living room, which is not the same as where the crawl space was. Fortunately we had to tear out the gas wall heater unit, and had a perfect little space to run the pipe, and an outlet nearby. Popped out the roof where the old vent pipe was, and called it good. If I am in the closet that it is in, I can hear it. When it was installed, the pipe just went about 1', then the fan, then 3' of pipe and a 90º bend. After we put on the deck, and replaced a window, we decided we didn't really want radon blowing right at us, so I extended it.

Before
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After
1607405558619.png

The third we put in when we built the garage, hoping we could get by with a passive system, so we laid down the perforated pipe, gravel, and connected it to a pvc pipe. When we tested, the numbers were really high, so we ended up having to put in a fan and running a 30' gutter from the fan.

1607405791637.png
1607405812701.png
 
Oct 15, 2020
153
New Hampshire
The sellers installed the sub slab system and it brought the numbers on the test down to 2.8. Not fantastic BUT they still hadn’t sealed the Crawlspace which is connected to the basement. I’m hopeful once the vapor barrier is down, the radon numbers will drop.
Also over time I’m guessing it may go down a bit more in that basement. When I went by a week or so after the test, the gauge read 1.8pci but who knows how accurate that was since we had opened the bulkhead at that time.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,597
Northern NH
Did they do a test on the well water? (assuming its a well).
 

peakbagger

Minister of Fire
Jul 11, 2008
6,597
Northern NH
Radon sinks to the lowest point, if you put in a heating system try to get the combustion air intake down low near the floor. I knew someone with a granite foundation that reduced his numbers by routing their barometric damper inlet down to the floor and pulling boiler combustion air from the floor. (He did have to put in an air filter box over his boiler combustion air to keep sawdust and woodchips from getting in his boiler air inlet. He has a very old home not particularly air tight. I do not think this would work with a modern tight home.
 

John Galt

Burning Hunk
Oct 22, 2019
116
W Montana
The mitigation system won't affect humidity noticeably.

On a side note, the sellers aren't required to fix anything in the house. Any repairs that are requested to be done are part of the negotiations, they can be accepted or rejected.
 
Oct 15, 2020
153
New Hampshire
Radon sinks to the lowest point, if you put in a heating system try to get the combustion air intake down low near the floor. I knew someone with a granite foundation that reduced his numbers by routing their barometric damper inlet down to the floor and pulling boiler combustion air from the floor. (He did have to put in an air filter box over his boiler combustion air to keep sawdust and woodchips from getting in his boiler air inlet. He has a very old home not particularly air tight. I do not think this would work with a modern tight home.


Interesting idea; I'll discuss with our installer for the Pellet System. See what can be done.