slow death by radon or quick by CO?

[jmiller_2308]

Short story:
The current incarnation of my radon mitigation system seems to be causing enough of a back draft that my naturally aspirated boiler exhaust backs up and sets the CO alarms off always during the wee hours of the morning. I hate being woken by an alarm at 2:00 am but it is better than not waking up. Currently the radon mitigation system is off while I wait for the next round of "fixes".

Background and longer story:
Last fall I bought a AirThings radon meter (junk) to check the radon in my house. It registered just over 4 so I decided to get a radon mitigation company to install a system. They installed a 3" pipe running from my sump basket into the conditioned garage through the attic and out the roof with the fan in the attic. When the weather cooled enough that windows remained closed and the boiler kicked on I noticed the AirThings indicating over 6.

Since the radon mitigation company guarantees a certain level of performance they came back and replaced the pipe with a 4" pipe and a bigger fan only the AirThings didn't seem to show any changes to radon levels. I bought another AirThings and while the original AirThings was reading in the 4 to 6 range the new one was reading 8 to 11. The AirThings people told me to wait a month for things to stabilize even though I'd been already testing for more than a week.

Since the 2 AirThings were so divergent I bought a charcoal test to try to verify if one of them was more accurate than the other. The carbon test registered right in the middle of the 2 AirThings.

OK, so clearly the 4" pipe and bigger fan didn't help and the mitigation company comes out and installs their biggest fan in my attic. It is starting to sound like a jet outside and inside there is a bit of a rumble in the far end of the house. Wait a week, and nothing changing on the AirThings. I buy a Radon Eye because it can register in 10 minutes and continue my war with AirThings to have them explain the difference and either refund of replace the worthless meters. The Radon Eye is indicating levels in the 7 range so I call the mitigation company again.

BTW: After declaring war on AirThings the company finally relented and sent me one replacement AirThings which didn't agree with the reading from any of the other meters. So much for their warranties and guarantees Crappy company - stay away

The mitigation company came back and installed a second 4" pipe running next to the previous pipe with yet another mongo fan - now it sounds like a bunch of jets outside the house. I wait a day and the radon eye seems to be indicating that the radon might finally be trending below 4 but then after a few days at 1:30 in the morning my CO alarms go off - WTF - nasty way to wake up. Open windows, turn off boiler, and look for the meter that is alarming which of course was the one in the boiler room. The CO meter with numbers just outside the boiler room read 0 and went to 0 in the boiler room by the time I moved the meter there. At this point I thought maybe the alarm in the boiler room was malfunctioning. I happened to have a spare so I replaced the alarm in the boiler room flipped on the boiler and immediately felt a lot of exhaust coming out the vent and of course the meter with numbers climbed and the new alarm went off. Turned off the boiler again and watched the numbers go to zero quickly. Left the furnace off and went to bed.

Woke up to a colder house and started trying to contact my HVAC guy as well as to let the radon guys know that although the radon levels were trending down that the numbers may not be accurate as I had to open windows for a CO issue. The radon guys got back to me and said... ya, the back draft CO issue is likely because of the new fan they installed and they recommended adding another 6" make up air vent and switching off one of the fans until the additional vent is in place.

While waiting for my HVAC guy I tried the single fan and got to enjoy a 2:30 CO alarm wake up call. I know the drill by now so boiler off, windows open, watch the meter go to zero. TURN OFF THAT DAMN RADON SYSTEM ALL TOGETHER!!

HVAC guy shows up the next day and installs another 6" vent and wonders why the radon guys didn't do something. I'm starting to wonder that as well. Turn on the radon and we are good for a day and then the next night another CO alarm wakeup call around 2:00 am. Dang I'm getting tired of this - TURN THAT DAMN RADON SYSTEM OFF AGAIN - better to die slow agonizing radon death then deal with this.

I talk to the radon guys again and they keep saying that I must have a monster leak in my foundation someplace. They have a new concept that is to relocate the second pipe about 10' from the sump basket directly into the gravel. This means removing built in place cabinets so they can drill into the concrete floor which itself is a pain but considering it is the wife's craft room means it is become increasingly painful for me.

I have already begun preparing for the removal of the cabinetry and am actively trying to nudge the wife into getting her stuff out of the room. I hope to be on the radon guys schedule again soon to give them one last try at fixing this thing. If moving the second pipe doesn't create some noticeable changes f**k it, rip the **** out and let me die slowly.

I'm not sure if the radon guys are inept or there is really something messed up with my house. At this point the radon guys are continuing to work for free and are significantly under water on this job so it is hard to walk away from them but if I did, how would I find/trust some other installer? Before these guys I had recommended outfits that ghosted me and others that when I checked into their work they no longer existed because they were so crappy.

 

[kaymccampbell]

Sounds like me and the new range hood. Prior to installing the range hood I did some serious sealing up. So when I turned on the range hood, or any exhaust fan in the house the fireplace would spout ash through the gap between the glass doors, and when winter came, the boiler would shut down on rollout, too. I've now got one 6" and three 8" powered makeup air vents.

As to the radon mitigation. Some places on earth can really pump out the radon. An acquaintance, in a small farmhouse of maybe 800 sqft on the ground, who lives on a particularly hot bit of rock, has eight 4" tubes coming out of their new basement slab, running through a huge makeup air heat exchanger. You can say they should just move, but the house has been in their family for centuries, and it wasn't until they decided to institute energy conservation measures that things went south.

I'd let the radon people keep trying as long as they're willing. You're lucky in that respect, as so many radon abatement firms are fly-by-night at best.

 

[danski0224]

The boiler needs a fan powered combustion air intake system and the controls to turn it on when the boiler and/or water heater is on.

With or without a CO exhaust fan.

You probably also need some sort of ERV to balance the air being removed by the CO system.

 

[pcmeiners]

"slow death by radon"..... it ain't that slow

You must have a massive leaks in your basement. I had a level of >75 pico, self installed 4" pipe takes care of it, even with a lot of very small cracks in my 26 by 50 basement and block walls. My tester is a Radex unit, accurate enough, shows logs and graphs. If you have block basement walls, a very possible radon avenue, you can paint with special sealing paint. If you have a sump for sewer access , needs to be sealed.
Weather has a large influence on radon levels, rain... snow, rain, or frozen ground forces radon to find the least resistance... your basement.
On my system I have two 4" mufflers in the attic, one before and one after the fan; I can hear my neighbors if outside, not mine, inside I can barely hear it. Purchased on Ebay, they were reasonable, retail they are high priced. If you purchase do not purchase any with foam inside, get fiberglass; foam will deteriorate with age. Is your sump capped off with a cover as linked....

The Original Radon/Sump Dome - Sump Pump Accessories - Amazon.com

The Original Radon/Sump Dome - Sump Pump Accessories - Amazon.com

www.amazon.com

 

[Jackfre]

Suggest that you look at the Tjernlund Enforceer for the combustion air for the boiler. They are a local company for you.

 

[fitter30]

If you build a insulated room around the boiler and water can bring combustion air into the room at 1 sq. In. Per 4000 btu's. 130,000 btu's = 32.5 sq "
With a fan
6500 cu ft

Combustion Air Requirements – InterNACHI Inspection Narrative Library

 

[TurnipTruck]

Did I miss a description of your heater?

It sounds like your boiler and/or water heater are not high efficiency models with plastic pipes to the outside for the exhaust and intake.

 

[pembol]

I generally thought that Radon mitigation required sealing and ventilation? Are they just trying to fix this with bigger fans, or did they work on sealing the sub slab area from the living space? A huge fan is just using a lot of energy and pulling conditioned air out of your house, and apparently out of your furnace.

I also live in a high radon area, our prior house had an active radon system with a fan, but in our new house we did a good job of sealing under the slab with a membrane, and now just have a passive system, which is basically a vent stack from under the radon barrier to above the roof. This has been keeping our average radon well below 4.

We have had good luck with our Airthings radon detector - on average it was very close to a week long charcoal test. One thing to realize with Radon monitoring is that the decays which the sensors detect are very, very infrequent. One pCi/L is 37 Bq in metric units, which is 37 decays per cubic meter of air per second - however the sample volume on the real time detectors is really low - like 1mL, so 1 pCi/L only produces one count every 30,000s or about every 8 hours. 4 PCi/L is one count every 2 hours. This is why you have to leave them for a week or more to get a a meaningful reading - it takes that long to accumulate a meaningful signal, and the instantaneous values between two meters sitting right next to each other are unlikely to be the same based on statistics.

 

[The Bean]

I remember when the radon craze took off, coincided with the super energy conservation trend and air tight houses. Mine is nearly 100 years old now and the original steel casement windows are drafty enough that I don't concern myself with radon. I've got a CO detector plugged into the wall outlet on the landing between first and second floors. The only alarms we ever get is smoke detector next to the kitchen when the wife is broiling a steak.

 

[Junkdrawer Dog]

A sidewalk salesman was desperately trying to sell me replacement windows. He pointed out my old builder grade aluminum sliders and suggested that they must be terribly drafty. I told him that was fine because it kept the radon and carbon monoxide levels low. He left.

 

[Buckaroo5]

The radon mitigation systems I am familiar with drill through the slab and vent the gravel sub-base. Then all the cracks in the walls and slab are sealed and a cover is put over the sump pump hole which is sealed with silicone. It sounds like you are currently venting the basement which is a huge source of energy loss in the winter and will draw air (and radon) in through all the cracks and crevices. I don't understand how that is supposed to work. It's no wonder the readings have gone up.

 

[jmiller_2308]

Thanks for all the replies. I'll try to address the comments here:

• The house is a large walk out rambler with the basement 90% finished so addressing any block issues now is not easy or palatable. The floor is largely carpeted so it isn't easy to talk about looking for cracks to seal in it but in the areas that are not covered there is no indication of cracking. Being a walk out only a portion of the front of the house is actually under ground so ultimately probably no more than 40%.
  
  
• I had the house built in 1996 so I know its full history. It was built tight with an air exchanger. Last year all of the crappy pella windows were replaced with Andersen 400 series windows and stucco redone as they were not replacement but regular windows that required cutting out stucco to seal the window properly. The house is likely tighter now than it has been but there were no issues until the second radon fan got installed.
  
  
• The house has radiant heat floors in the basement and forced air via an air handler that is fed from the boiler for the entire house. Because of the radiant heat there is foam between earth and the slab. The boiler is not a HE boiler but is instead a naturally aspirated heavy cast iron Weil Mclane boiler with 96000 BTU input. There are now 2 6" air makeup air tubes feeding the boiler room. The boiler also produces hot water through an indirect water heater so no other sources of combustion in that room. The boiler room is a closed room of almost 200 sqft in size.
  
  
• The house has drain tile around the perimeter emptying into a sump basket that is in a different area of the house about 40 feet from the boiler room. When the radon system was installed it got installed through the sump basket cover and the basket was sealed. After the last attempt the installers cut additional holes in the sump basket to try to improve suction. BTW: I live on top of a hill with the water table significantly below my lowest level; the sump has never had water in it nor was it ever plumbed with a sump pump.
  
  
• If you can believe that any of the 5 different measuring devices I've used are somewhat suggestive of the actual radon levels I am glad that the worst has only barely read above 10 with and without the mitigation system on. Having the system off for the past number of days I also average the 3 remaining meters to be in the 5 to 6 range when windows were closed. So this isn't healthy but at least I'm not seeing double digits.
  
  
• I like the idea of a forced draft on the exhaust but I'm going to leave those discussions up to my HVAC guys; I just don't want to f around with CO and combustion issues.
  
  
• The installers are now scheduled to come out Monday 3/17 to drill a hole in the slab down to the gravel and move one of the 2 pipes to it. The hole will be in the same room as the sump basket and be about 10 feet further into the house.

 

[PCustoms]

Without sealing the basement all you are doing is sucking the semi-conditioned air and a tiny bit of radon out.

At 5-6 you're barely about the threshold. With levels barely at 10 having 2 systems is insane

Is the current pipe below slab, or just stuck in the sump put? Sounds like a poor install.

 

[The Bean]

I bet the joint between slab and bsmt walls is a 1 or 2" gap that is not sealed... maybe.

 

[PCustoms]

I bet the joint between slab and bsmt walls is a 1 or 2" gap that is not sealed... maybe.

That's huge...

I bet if he had sealed the slab the level would have dropped.

I've heard the puck tests can be wildly inaccurate.

 

[PCustoms]

To answer the original question (I assumed it was a joke), CO will kill you today, radon may make you sick over years of exposure.

Focus on the CO issue first

 

[The Bean]

He said there is foam between earth and slab for the infloor heat. Maybe that expansion joint is not filled. I've seen it before.

 

[PCustoms]

He said there is foam between earth and slab for the infloor heat. Maybe that expansion joint is not filled. I've seen it before.

Yep, read that wrong. Edited my post

 

[micromind]

I think they installed the fans backward.......it seems to me that if the fans blew outside air into the building and maintained a positive pressure inside, the radon would stay in the ground.

 

[PCustoms]

I think they installed the fans backward.......it seems to me that if the fans blew outside air into the building and maintained a positive pressure inside, the radon would stay in the ground.

That's not how radon fans work.

 

[Jeepster04]

The radon mitigation systems I am familiar with drill through the slab and vent the gravel sub-base. Then all the cracks in the walls and slab are sealed and a cover is put over the sump pump hole which is sealed with silicone. It sounds like you are currently venting the basement which is a huge source of energy loss in the winter and will draw air (and radon) in through all the cracks and crevices. I don't understand how that is supposed to work. It's no wonder the readings have gone up.

That's always been my understanding as well. The ones I've seen have one fan on a manifold with a pipe to the sump pit and pipes pulling from under the conc. slab.

Simply putting a pipe in an open sump pit will do nothing. This company probably isnt use to people having actual Radon issues.

Opening just one vent in my crawl space caused my Radon levels to drop below 1.

 

[jmiller_2308]

Humorous (or not) comment about the fans being backward. Mine are not but the last time the installers were here they were describing a job they just came from in which they were replacing a fan that was making noise. When they got there they found the fan that had been installed previously was indeed installed backward. Since the fans have arrows on them it is kind of baffling to see how anybody, much less a professional, could screw up that badly. That client was a 90+ year old woman whos son had been living in the basement until he had recently died of esophageal cancer. Coincidence or not?

Back to my issue, my installers have out lasted, and repaired installations, from many of the fly by night radon companies in the area. I'm still not sure if they are competent but they speak well and have good reviews. They are also standing behind their guarantee so I'll let them run for a bit longer.

I have heard of lots of installations using just the sump basket so long as it is sealed and this is exactly the approach they took for my house. On one repeat attempt they cut holes in the basket to help ensure better flow from the gravel but that proved insufficient. Now that the issue continues to escalate, on Monday they will drill through the concrete to move one of the sump basket pipes directly into the gravel. Drilling into the concrete has been a concern because of the in floor heat but my pictures from the build should prevent any issues.

Since the basement is largely finished and carpeted it is not easy to visually inspect for possible gaps. I have looked in the unfinished areas and see no cracks so I am hopeful that is somewhat representative of the rest of the house. Yet there is still apparently a large air leak someplace. I have tried walking around with a candle to identify drafts but I see very little if any deflection of the flame. I tried walking around with a smudge stick to look for smoke movement but quickly gave up on that as I didn't like all the smoke in the house. I tried moving the Radon Eye around to see if there is some area of the house that has radically different radon levels but every place seemed pretty consistent.

People seem to be convinced that my radon system is sucking inside conditioned air out of the house rather than radon from under the slab. Is there any other test other than flame, smoke, radon eye, that can be used to detect a "monster" air leak into the house?

 

[danski0224]

Is there any other test other than flame, smoke, radon eye, that can be used to detect a "monster" air leak into the house?

Blower door test.

 

[The Bean]

Blower door test will open a can of worms, possibly, but I agree, it's the best leak detector.

 

[pcmeiners]

I think they installed the fans backward.......it seems to me that if the fans blew outside air into the building and maintained a positive pressure inside, the radon would stay in the ground.

Yes that would work but positive pressure ventilation would be a very expensive form of Radon mitigation due to heat loss and power usage, it is not used often.

For one test I would cut a hole in the basement Sheetrock, place the tester within the cavity, seal it with plastic, perhaps in wall areas, north, south, east, west.

Since the house is relatively new, floor cracks should not be a major Radon issue, even if unsealed.
For a Radon system to work properly the slab must have a decent gravel depth base. Also it is also a good idea to clean the gravel with a pressure washer, or at least a full flow hose around your mitigation pipe. I did this to my pit area, I washed the gravel approx 6 feet in all directions.

If you can seal your floor sheathing gaps, pipe, or electric holes, your floor area above should have almost no Radon, rather tedious but can be done. Foam in can does a good job with a professional applicator such as......

https://www.amazon.com/Picowe-Expanding-Caulking-Application-Applicator/dp/B06XHP5QR1/?tag=atomicindus08-20

The mufflers I have are longer (24"), but same brand, again fiberglass, foam is a scam. On the other hand, they could be made cheap out of PVC and a 1" thick mat of acoustic fiberglass, and some mesh screen.

6" Duct Muffler / Silencer | eBay

For use with inline 6" fans to dampen noise

www.ebay.com

Lastly with Radon around 6 pico, many with Radon issues would be happy.

 

[finn]

If they’re going to drill through the hydronic floor, make sure they positively locate the heating tubes with an infrared camera before drilling.

 

[bonneyman]

Reminds me of an old Star Trek episode:
"Mr. Spock, we seem to have been given a choice. Death by asphyxiation, or death by radiation poisoning."

 

[jmiller_2308]

I had been hoping to find "monstrous" air leaks through homeowner remedies but perhaps it is time to call in the professionals and do a blower door test. I did just have all my windows replaced so I assumed no leakage there but then again... it was the window project from hell.

Thanks for the idea of verifying radiant heat location with an infrared camera. I have lots of pictures but it is certainly prudent to verify before drilling.

 

[larry4406]

Interesting read....

Some background on our system in our new homes and then a few troubleshooting cases chasing high radon events with it. Perhaps this might be helpful.

• 3" PVC passive radon vent to the sump crock and it vents thru the roof. The sump lid is gasketed and sealed to the basin. We install an outlet in the attic proximate to the vent roof penetration of a future fan/air pump.
• 4" concrete slab with 6 mil vapor barrier on a 4" gravel bed of #57 VDOT stone
• Sikaflex sealant of concrete slab perimeter to foundation wall
• 4" perforated drain tile runs around inside perimeter of house footing within the gravel bed and is routed to the sump crock
• Footing has 2" weep holes thru it every 6-8' of footing length. This equalizes groundwater across both sides of the footing
• 4" perforated drain tile runs around the exterior perimeter of the house footing. This is contained within a gravel bed and covered with filter fabric prior to backfill
• Foundation walls hot spray tar GMX waterproofing

In fully buried basements, we offer an areaway, which is a set of concrete stairs and side walls from the basement up to grade on the exterior. The landing at the bottom of the stairs is 4" stepdown relative to the basement slab and the landing has a trench type drain with a 3" pvc pipe (no pea trap) run to the sump basin. The 3" drain pipe enters the side wall of the sump basin at about mid-height (we use 36" deep sump basins).

With a walkout basement, we daylight the exterior draintile, so gravity naturally lets any groundwater freely runout vs taxing the sump pump.

With this background, here are 2 case histories of me trying to get some homes to reduced radon levels after we had activated the passive system via addition of air pump in the attic and installation of the manometer visual indicator in the basement on the 3" pipe from the sump basin. This events have played out on several homes.

• The buried basement houses with areaway, saw almost no reduction in radon levels and the manometer gauge showed that the fan/air pump was not pulling much sub-slab vacuum. We determined that air was being pulled into the sump crock via the areaway drain and being exhausted by the fan/air pump vs pulling a sub-slab vacuum. The solution was to install a 90 degree elbow on the 3" drain pipe pointed downward and adding a short vertical length of pipe with the pipe end below the standing water level in the sump crock. This "snorkel" stopped the intrusion of air from the drain pipe via the water seal, the manometer gauge showed a marked increase in sub-slab vacuum, and radon levels dropped well below the threshold criteria.
• Several of the walkout houses also showed almost no reduction in radon levels and similarly the manometer gauge showed minimal sub-slab vacuum. We determined that air was being pulled into the daylight draintile, thru the gravel bed, footing weep holes, and thru the perf pipe. We excavated, capped, and eliminated the daylight draintile ends. This stopped the intrusion of air via the draintile, the manometer gauge showed a marked increase in sub-slab vacuum, and radon levels dropped well below the threshold criteria.

Sorry for the long read.

Edit - our furnaces and water heaters are piped direct with outside combustion air.

 

[danski0224]

I did just have all my windows replaced so I assumed no leakage

Bwaaahahahahahaha

(breath)

 

[dscheidt]

I had been hoping to find "monstrous" air leaks through homeowner remedies but perhaps it is time to call in the professionals and do a blower door test. I did just have all my windows replaced so I assumed no leakage there but then again... it was the window project from hell.

Thanks for the idea of verifying radiant heat location with an infrared camera. I have lots of pictures but it is certainly prudent to verify before drilling.

thermal camera will show air leaks around windows and doors pretty well, too, especially if you do it when it's cold out.

 

[pcmeiners]

What the significance of leak free windows? The tighter the windows the higher the radon levels (and CO) will be without proper mitigation; extremely unlikely high radon concentration could come from the outside.

 

[larry4406]

Make sure you have a cold air return in the basement. Run the fan periodically.

Remember the old phrase, “The solution to pollution is dilution”.

 

[jmiller_2308]

Thanks for the in depth discussion @larry4406 . I remember seeing many of your steps done when my house was built 29 years ago. In particular the drain tiles in and out of the cinder block, the tar like substance sprayed on the outside. I don't remember plastic between earth and cement but that is likely because the foam was already placed sometime between visits to the site. I do not recall any weep holes but that doesn't mean they weren't done. The house is a full walk out basement but there was no drain tile open to the outside.

When the system is on my manometers show significant deflection so I don't see the issue that @larry4406 is describing.

I've been busy so I haven't had an opportunity to locate an infrared camera yet but I'm working on it. Installation guys come back tomorrow afternoon to drill a new hole and I'd really like to confirm we know where the radiant heat pipe is before they do. Using the camera to look for other leaks would be good now as well especially since it got cold again.

 

[micromind]

What the significance of leak free windows? The tighter the windows the higher the radon levels (and CO) will be without proper mitigation; extremely unlikely high radon concentration could come from the outside.

Spend tons of money making a house tight enough that you need to spend tons more money making the air inside fit to breathe.........

 

[jmiller_2308]

More info but still not a solution

The installers were here Monday and were able to move one of the 4" pipes from the basket to a new hole drilled through the concreate and into the drain tile at about 10 feet away from the basket. In the process we learned the following:

• The hole showed my house was built with 4" of concrete, foam, plastic, cactus board, drain tile, gravel.
  
  
• When both fans were fired up there was significant suction from the new hole away from the basket and presumably around the whole house and back into the basket but not very much from the new hole back 10' to the basket. It seems like there might be some blockage in those 10' but that needs to be still explored.
  
  
• It was warm here yesterday and the house had a good deal of solar gain which meant that the boiler didn't run all afternoon or early evening. The mitigation system was on for roughly 3 hours before I forced the boiler to run to see if there might be an issue in the middle of the night. Sure enough, when the boiler fired it struggled to get a good draft going up the cold chimney. It didn't send all the exhaust into the room nor did it produce enough CO to even register on the meter but I could feel more heat coming out the bottom of the vent than is normal. The boiler did eventually succeed in inducing enough of a draft that the exhaust was flowing correctly but I didn't want to take any chances and shut down the mitigation system again hoping to get a good night sleep (sigh... clearly that didn't happen)
  
  
• Cactus board was commonly used in this area from the 90's through 2008 when building codes no longer allowed it because it was interfering with radon mitigation systems. My house was built in 1996 and has the cactus board installed under the slab and wrapped up the block foundation to be exposed a few inches above the slab. Plastic runs on top of the cactus board under the slab and continues up the foundation wall to the top of the cement foundation. This is supposedly great for keeping the basement dry but it is definitely a huge source of air/radon infiltration.
  
  
• My interpretation is that with the mitigation system on it creates a negative pressure in the house by sucking inside air out through the cactus board, into the drain tile, and out the roof. I couldn't detect specific drafts using my candle and other tests because the leak isn't localized, it is rather likely that it is the entire perimeter of the house.
  
  
• So why does my boiler backdraft and cause a CO alarm on only certain days and always in the middle of the night? My assumption is that both outside pressure and temperature impact when the issue occurs. That basically you have to recreate the issue I saw last night which is that the boiler and flue cool down enough that it creates a challenge for the boiler to create a draft on startup. Add in the negative pressure from the mitigation system and then the backdraft occurs. So with my setback thermometer and solar gain during the day it likely takes until the wee hours of the morning for the house to cool enough that the boiler fires and then I get the nasty wake up from my CO monitors.

My next step is to do some experiments with capping the pipe in the basket and turning off its fan to see if that helps or to possibly go to a smaller fan. I suspect this will only delay how long it takes the house to create a hazardous negative pressure and that ultimately I'm going to end up cutting up drywall to seal all the cactus board.

 

[larry4406]

I have never heard of Cactus Board and had to google it.

Home

Keep the Basement and Foundation Dry with CactusBoard Foundation Waterproofing for New Construction. It works for home builders, construction crews, and homeowners plus it is easy, inexpensive, and warranted for 20 years! Contact us for more information!

www.cactusboard.com

So Cactus Board is dimple mat that sits on the footing and adjacent the interior of the foundation wall. Then the slab is board. The cactus board lets any moisture on the interior side of the walls drip downward, thru the crevices, and travel to the gravel bed.

Well this crevice is also letting in your radon. We don't use any gizmo here in new construction. Slab is poured tight to the walls and after cure and before framing, we seal that cold joint with a Sikaflex product.



I think I would look seriously into providing the boiler with a direct source of outside combustion air vs pulling it from the interior space. I would chase that first vs tearing out all of your drywall to seal off the Cactus Board crevice.

I edited my prior post to state that our water heaters and furnaces are provided with outside combustion air.

 

[jmiller_2308]

I have never heard of Cactus Board and had to google it.

Home

Keep the Basement and Foundation Dry with CactusBoard Foundation Waterproofing for New Construction. It works for home builders, construction crews, and homeowners plus it is easy, inexpensive, and warranted for 20 years! Contact us for more information!

www.cactusboard.com

So Cactus Board is dimple mat that sits on the footing and adjacent the interior of the foundation wall. Then the slab is board. The cactus board lets any moisture on the interior side of the walls drip downward, thru the crevices, and travel to the gravel bed.

Well this crevice is also letting in your radon. We don't use any gizmo here in new construction. Slab is poured tight to the walls and after cure and before framing, we seal that cold joint with a Sikaflex product.



I think I would look seriously into providing the boiler with a direct source of outside combustion air vs pulling it from the interior space. I would chase that first vs tearing out all of your drywall to seal off the Cactus Board crevice.

I edited my prior post to state that our water heaters and furnaces are provided with outside combustion air.

The cactus board in my house looks more like corrugated cardboard but it is the same concept as what you found.

My house has two 6" make up air vents feeding the boiler and the boiler runs an indirect water heater so no other forms of combustion in the boiler room.

I need to talk to my HVAC guy to see if it might be possible or wise to add some sort of induced exhaust to my existing normally aspirated boiler like those used on condensing boilers.

 

[danski0224]

My house has two 6" make up air vents feeding the boiler and the boiler runs an indirect water heater so no other forms of combustion in the boiler room.

"Gravity" combustion air systems act like a chimney. They do not necessarily work as assumed.

You could get a smoke pen, light it, and put it by the combustion air outlet in the basement and by the boiler flue and see what happens when the radon system is operating.

I need to talk to my HVAC guy to see if it might be possible or wise to add some sort of induced exhaust to my existing normally aspirated boiler like those used on condensing boilers.

Same issue will remain, the house will be negative pressure.

Boiler needs a powered combustion air system.

 

[The Bean]

Cactus board, eh? So, it's that perimeter joint as I suspected that is not sealed but open for some cocamamie drainage scheme. There's your problem, lady. 🫤