Did I Mess Up My OAK?

[iron]

I now live in BC in the rocky mountains. We installed a ZC fireplace and it's been great. Burns really clean.

We have a new home (2022) and it's quite airtight - basically a net zero passive house without the certification. However, I saw something on CBC (Canadian PBS) talking about hidden radon dangers throughout Canada due to the amount of rockiness throughout the country. Sure enough, I bought a monitor and found ours to be moderate-to-high for a 30+ day period. We have a radon collection pipe already installed, so I cut out a segment and installed a fan. Two days later the radon dropped to near zero, but then, when we lit our next fire, backdraft! Smoke coming out through the door. Cold air spewing in through the OAK or flue. No bueno.

So, what can I do to rectify this situation? We have an HRV and it's set to auto. I wonder if it should be set to continuous so that it's constantly working to balance the negative pressure that's been created by the radon fan. I assume it's better to be pulling in air at 20% loss in energy vs 100% loss (or whatever it would be). Maybe I need to bite the bullet and downsize the radon fan, but it's hard to swallow $300, especially if I don't know if a smaller model will work the same.

Appreciate any insight!

 

[Winterpeger]

Our 1650sq ft. bungalow constructed in 2014 was placed on a 5-foot high icf foundation and the joist cavities were spray foamed for insulating and air barrier requirements. Polly was installed and sealed prior to concrete rat slab installation. I installed a radon fan in 2020 due to a reading of over 300 bq/cm in the crawl space. I could not detect any difference in our wood stove operation with the radon fan running or not. The heat recovery ventilator when properly installed exhausts the same amount of air that it brings in, therefore it is in a "balanced" state. I did caulk the interior slab to wall joint in the crawl space. Radon fan is runnig about 60 cfm.

 

[iron]

Yeah, I guess 60 CFM is a big difference from the 345 CFM I have. Maybe I just need to contact a local radon tech and have them test out fans. Obviously, getting the radon out of the house is priority #1

 

[Winterpeger]

To determine what the fan is actually flowing in your situation you have to take a measurement at the suction side and take that and reference the fan curve. That will tell you how much air the fan is actually moving. As a side note the foundation contactor asked me to install the sub slab 4-inch drain for the waste and the future radon mitigation. Not knowing, I installed a 6-foot-long piece about a foot out from the outside wall. Crawl space is actually about 60 feet by 27. Drilled a 3/16 inch hole in the slab at the other end of the space (50 feet away from the sub slab radon pipe inlet) where I could take measurements with my magnehelic gauge. The large fan I had had purchased in 2022 was drawing .03 inches at the slab test port. The only problem was mid-January the fan was drawing in so much air the ground under the slab froze thereby lifting a portion of the concrete slab. I then purchased the small fan I am using now. This winter I left the fan running during our vacation south (3weeks) and came back to the slab lifting, same place. This summer I will be moving the fan suction point to the middle of the slab, lesson learned.

 

[kborndale]

Instead of replacing the fan couldn't you just get a fan speed controller hooked to it? You could turn it low in heating season and turn it back up in the summer.

 

[Whitenuckler]

I now live in BC in the rocky mountains. We installed a ZC fireplace and it's been great. Burns really clean.

We have a new home (2022) and it's quite airtight - basically a net zero passive house without the certification. However, I saw something on CBC (Canadian PBS) talking about hidden radon dangers throughout Canada due to the amount of rockiness throughout the country. Sure enough, I bought a monitor and found ours to be moderate-to-high for a 30+ day period. We have a radon collection pipe already installed, so I cut out a segment and installed a fan. Two days later the radon dropped to near zero, but then, when we lit our next fire, backdraft! Smoke coming out through the door. Cold air spewing in through the OAK or flue. No bueno.

So, what can I do to rectify this situation? We have an HRV and it's set to auto. I wonder if it should be set to continuous so that it's constantly working to balance the negative pressure that's been created by the radon fan. I assume it's better to be pulling in air at 20% loss in energy vs 100% loss (or whatever it would be). Maybe I need to bite the bullet and downsize the radon fan, but it's hard to swallow $300, especially if I don't know if a smaller model will work the same.

Appreciate any insight!

You now have me worried. I was looking at buying a meter. Is that a good idea or should I buy a test kit you send away? My family never did it when I was growing up, and I have never did it before. I wonder if I should start to worry about it now?

 

[Dieselhead]

I think everyone should test. I always thought only people on ledge would have radon. My house is built on an old gravel pit, very sandy soil. It turns out after a free test through our local health dept. that I have radon in the basement. I’ve since remediated it but on a hunch tested my well water also. Turns out it’s in the water too so I installed a radon bubbler to handle that.

As far as the stove the radon fan should be creating negative pressure under the slab outside the house so make sure the issue is caused by the radon fan and not another source creating negative issue. I’d unplug the fan temporarily while reloading and see if it goes away.

 

[GG Woody]

Yeah, I guess 60 CFM is a big difference from the 345 CFM I have. Maybe I just need to contact a local radon tech and have them test out fans. Obviously, getting the radon out of the house is priority #1
View attachment 346975

Like @kborndale mentioned, I would try a speed controller on that fan. 345 would be a lot of cfm if it was actually running at that speed, like almost half of a small furnace! (approx. 400cfm to run 1 ton of cooling)
Some fans have different wires already in the junction box to enable different speeds as well.
Good on you for addressing the radon, that is something I should be doing....

 

[EbS-P]

You now have me worried. I was looking at buying a meter. Is that a good idea or should I buy a test kit you send away? My family never did it when I was growing up, and I have never did it before. I wonder if I should start to worry about it now?

Publication information - Government of Canada Publications - Canada.ca

Publication information / bibliographic Record.

publications.gc.ca

 

[EbS-P]

AI says you should target 3. To .5 air exchanges per hour. Find the cu ft of you basement and do the math to see why flow rate you need. Again this all depends on radon levels. 300 cfm is way too high.

 

[stoveliker]

huh?
you don't want air exchanges in the (living space of the) basement.
You want to create a vacuum *under* the slab, so that any radon coming up from the soil gets sucked into the fan and exhausted above the roofline, to *prevent* it from coming into the basement.
If your slab and radon fan lines are sufficiently sealed, a radon fan should not result in negative pressures.

I had a system like that in TN.

 

[EbS-P]

huh?
you don't want air exchanges in the (living space of the) basement.
You want to create a vacuum *under* the slab, so that any radon coming up from the soil gets sucked into the ran and exhausted above the roofline, to *prevent* it from coming into the basement.
If your slab and radon fan lines are sufficiently sealed, a radon fan should not result in negative pressures.

I had a system like that in TN.

Great point!

 

[Whitenuckler]

Publication information - Government of Canada Publications - Canada.ca

Publication information / bibliographic Record.

publications.gc.ca

AIRTHINGS Corentium Home , Radon Gas Detector, Canadian Version in Bq/m, grey​

Just ordered. I spend a lot of time in the basement.

 

[Dieselhead]

Like @kborndale mentioned, I would try a speed controller on that fan. 345 would be a lot of cfm if it was actually running at that speed, like almost half of a small furnace! (approx. 400cfm to run 1 ton of cooling)
Some fans have different wires already in the junction box to enable different speeds as well.
Good on you for addressing the radon, that is something I should be doing....

just be sure to use the right speed controller, some will cause the fan to hum

https://www.radonaway.com/pdfs/radon-newsletters/DC-fan-controls.pdf

 

[EbS-P]

Radon seems to come up regularly on here. it’s not new. We know where all the hot spots are. Maybe radon testing should be required every time a house is sold?

 

[Whitenuckler]

Radon seems to come up regularly on here. it’s not new. We know where all the hot spots are. Maybe radon testing should be required every time a house is sold?

I bought this house in 2024, but don't remember if that was part the disclosure. Of course if you don't test, you don't know. If you do test, and it's way too high, it's too late. Then like you say, testing before you buy would be required.

 

[stoveliker]

Home inspectors (who work for the buyer) should demand radon data (by a third party) as part of the inspection, at least for areas known to suffer from radon.

Who doesn't like some radioactivity below their feet

 

[bigealta]

Radon tests also are measured over time (like 30 days or more). I have an Airthings Radon Meter in 2 houses and the radon fluctuates quite a bit in both houses. The average over time is what they say counts.
If you just do readings for a day or 2 you may be reading either hi or low extremes.

Also opening windows in the basement can drastically lower radon levels. I try to keep mine open as much as possible. Sometimes i use a fan in the window but it's not always needed.

 

[EbS-P]

Radon tests also are measured over time (like 30 days or more). I have an Airthings Radon Meter in 2 houses and the radon fluctuates quite a bit in both houses. The average over time is what they say counts.
If you just do readings for a day or 2 you may be reading either hi or low extremes.

Also opening windows in the basement can drastically lower radon levels. I try to keep mine open as much as possible. Sometimes i use a fan in the window but it's not always needed.

If you are on well water get that tested too

 

[bigealta]

If you are on well water get that tested too

City water in NJ and
Deep well sourced water from our small 500 family water company in Utah. Pretty sure i looked that up from the annual water test report. Not sure if they have bubblers in the holding tanks?

 

[Whitenuckler]

If you are on well water get that tested too

I'm on city water, and it comes from wells they have. I should be able to see if they test for radon in a report. My Dad built his home with a basement on shale rock. I helped hand dig a well on the property. The only tests done on it was when he built it 50 years ago.

 

[iron]

Yeah, I agree with the idea that the negative pressure should only be under the slab unless there are leaks. But, the basement slab is 8ft deep, so once you reach the edge of the slab, and hit dirt, I can't see where that much air volume would come from. Hard to suck air from dirt.

In the fan manual, it specifically states to not use a variable speed switch. But, when I wired the cord to the unit, there was a dial mounted to a free floating L-bracket that went from 1 to 10. There was a sharpie mark on the bracket next to the 10, so I assume this could be a variable speed switch. Guess that's my next step.

 

[stoveliker]

You don't need air volume.
You need low pressure at the piping before the fan, so that the few molecules of radon stream that way and thus not into the basement

In fact I heard water boiling sometimes when it was wet outside. Because the fan pulled a vacuum which lowoers the water boiling point and which indicates that not much air is flowing.

 

[Winterpeger]

I am an old, retired guy that spends far too much on the internet going down rabbit holes. Here is what I have observed, I will quote a few sources I have come across. Pressure reduction below the slab “Radon entry in houses has been effectively controlled with as little as -0.5 pa (-0.002" WC) pressure difference at remote pilot holes, however -2.5 pa (-0.01"WC) and greater should instill confidence the system will control radon.” That would be achieved through sizing the fan to the job not controlling its speed. Sub slab aggregate in new construction (I believe) is ¾ clean gravel 6 inches deep which allows for good drainage but also allows the air to move more freely in a radon mitigation system. Also, there is a vapor barrier laid out over the entire floor and fastened to the interior wall. Concrete poured directly on subsoil creates a whole different scenario. In my case the foundation wall is only 2.5 feet below grade, in the winter the soil around the foundation dries/freezes and slightly pulls away from the foundation allowing outside air to be pulled in under the slab, freezing the subsoil, and lifting the slab around 1 to 1.5 inches. In my case at the fan pulls .6 inches @ the fan location and the test port 50 feet away from the fan location I have a reading of .02 inches. In my case I must look at moving the intake or downsizing the fan.

As a side note water boils under a vacuum of 28 inches at sea level, I do not think these fans are capable of that much of a draw down. But I could and have been wrong in the past.

Don

 

[stoveliker]

I was surprised but it was unmistakable.
Well,.or I had a stream under the slab.
Come to think of it that is more likely indeed. So the sound was mistakable

Means the pump was larger than the expected air infiltration under the slab.

But yes, a small vacuum will pull all that's needed.
Same with a stove and chimney.