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