ERV/HRV for Radon Mitigation
Ours is a 100 year-old, 1660 sqft, two story house with a 710 sqft unconditioned basement in Western Massachusetts (CZ 5). I have done significant amounts of air-sealing and insulating in the basement and attic. However, I realize that the house is still probably quite leaky, despite my recent efforts.*
As a side effect, I have observed radon measures climbing from slightly above 2 pCi/L closer to 3-4 pCi/L. It’s not yet clear where the long-run average will settle, as some of it might be seasonal variation. Nevertheless, I’d like to address it if possible.
I’ve patched the basement slab where I could, but it is old, thin and not in great shape. I am thinking that a radon mitigation system may not work well with a leaky slab, and would mean we’d have an ugly exterior pipe.
My plan is instead to install some form of ERV/HRV system, as it would have the side benefit of improving IAQ. I am considering two options:
A.) Install two Lunos fans on opposite ends of the basement. This would likely address the radon problem at its source. We have leaky panned-joist returns for our HVAC system in the basement, so any improvement in the basement IAQ would likely transmit to the living area.
B.) Tie a Panasonic Intelli-balance 100 into our existing ductwork (simplified install), set to 50 cfm and use the ECM air handler to circulate the fresh air intermittently. I like that this solution would provide fresh air to the living area from a controlled source, rather than through random leaks. However, I worry that the ERV would overdry the house in the winter, even when used intermittently and at low cfm.
Does anyone have thoughts on these two options and the potential for overdrying?
*I am reluctant to get the house blower door tested, because there is exterior lead paint and god knows what else in those old walls.
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The best way to prevent over drying is to get your house tighter. You loose much more moisture through air leaks than you would through a high efficiency ERV. Blower door tests don't have be done with a negative pressure, they can also be done with positive pressure to keep any lead dust out. A bit more work but you can use smoke sticks or a fog machine to hunt down air leaks.
Adding in any ventilation will always reduce the moisture level in the house in the winter, there is no way around this. I would be more worried about IAQ than moisture, a spot humidifier can help if it really becomes an issue.
Venting radon with an ERV does work great, people have posed on here before about it:
https://www.greenbuildingadvisor.com/question/erv-best-practices-for-ventilation-and-radon-mitigation
For long term ventilation and air quality, I think the Panasonic unit is a better investment.
Thanks Akos, that makes sense. And thanks for the +1 on the Panasonic unit.
I guess this means you're less concerned about the energy penalty from using the air handler to distribute the air through the existing ducts? We bought this combo for our heat pump, based in part on your recommendation: https://www.carrierenterprise.com/ahri/206188253
I know you prefer a hybrid setup with dedicated returns, unfortunately that's not as feasible for us (there really isn't a good place to add a return in the kitchen).
99% of new builds have the HRV/ERV ducted using the simplified method. ECM air handlers on low use somewhere between 25W to 40W, not zero but not something I would loose too much sleep over.
The hybrid ducted setup is a good compromise for a new build where you can save the cost and installation of a couple bathroom fans. For a retrofit, the simplified install can be made to work.
The one item to watch for is running the air handler on fan only too much during the cooling season. This causes the condensate on the coil to re-evaporate which is bad for efficiency and humidity control. Less of an issue with a modulating unit as it should be providing some cooling most of the time. Something I would check next cooling season to make sure.
Provide an update once the winter hits on how the 38MARBQ24AA3/40MBAAQ24XA3 combo is doing, always good to hear real world experience for heat pump retrofits.
You can set up the ERV with a super simple duct configuration in the basement only. You could use just a single supply and return duct with registers at opposite ends of the basement. For the low ventilation rates needed, the ducts are not very large. I'm not in favor of using existing HVAC ductwork as it means the circulation fan must be run nearly full-time and that wastes more energy than the ERV itself. I also prefer balanced ventilation solutions, especially for basements with radon issues. If the basement runs at negative pressure, it can suck additional radon from the soils. If it is at positive pressure, then basement odors can be forced up to the living space.
Thanks Peter.
Your point about balanced ventilation in the basements with radon problems is well taken. I appreciate the suggestion of using a ducted ERV in the basement only with one supply and return register each instead of a Lunos e2 pair. I think I would have troubles installing the Lunos into the rim joists anyways.
Maybe this is too much guesswork, but could there be a version of the existing-ductwork approach that manages the radon but doesn't incur a huge energy penalty? In particular, would it help to call on the air handler only intermittently? According to the BSC formula, our house only really needs about 35 cfm, not the 50 cfm that the smallest ducted ERVs seem to deliver with continuous operation.
A follow-up puzzle: I went with option B and installed the IB 100. Unfortunately it didn't really improve the radon readings in a systematic way (I'm using an Airthings Corentium, which doesn't keep a detailed history).
I've tried various combinations of low/high CFM and continuous/intermittent operation, neither seemed to affect the radon. In one experiment, the readings even seemed to go up while the ERV was on the highest setting (100 cfm) and running continuously.
Does anybody have any ideas for what to to try next? I will try to keep working on sealing up the return ductwork in the basement, as continuous operation may be increasing the amount of basement air that gets redistributed in the house. If this doesn't help, I might install an exhaust fan in the basement only, as Martin suggests this strategy may actually lower radon despite the negative pressure (https://www.greenbuildingadvisor.com/article/exhaust-only-ventilation-systems-and-radon). The hope would be that more of the make-up air comes from the upstairs as opposed to the soil. Or install a dedicated ERV for the basement only?
I recommend installing a proper radon mitigation system. It is not cheap or pretty, but neither is lung cancer.
I would disconnect the ERV stale air pickup duct from the HVAC return. Cap the hole on the return.
Run the ERV stale air duct to the open space in the basement near the floor level.
The idea is that you are directly exhausting the air that contains the radon instead of trying to dilute it through circulation.
I would try to run like this for a couple of weeks with the ERV on max and see what happens.
Thanks Akos.
Is it possible to tell which approach will incur a higher energy penalty: increasing the ventilation rate of the ERV (say from 40 cfm to 80 cfm) vs. switching the stale air pickup location from the conditioned space to the unconditioned basement (i.e. going from 67 F to ca. 50-55 F)? I don't have a detailed power metering device, so I can't experiment with how it impacts the heating load for our heat pump.
Say you are running at 50CFM. The heat your heat pump now supplies to the basements is:
-50CFM * 1.08 BTU/CFM/DegF * (67F-55F)=648btu. For a house that falls into noise category, so not something I would be too worried about.
It is very hard to separate a basement from a house, it is pretty much part of the house. A cold basement mostly means cold floors above so a bit of extra heat there doesn't hurt. If you do get the basement eventually insulated, I would heat it to be a bit above house temperature as a budget floor heat for the main floor.
Hi there, I stumbled on this thread as I recently had a Carrier 38MURA/40MUAA heat pump system installed and am now onto the next project which is indoor air quality. I am considering an ERV as well, as a multi pronged approach to reduce CO2 levels, stale air, and radon levels with one system rather than getting a radon mitigation system which only helps with radon. I figure I can always add the radon mitigation system on top after the ERV if it's really needed.
I live not far from OP, in Toronto.
@noew Did you get your system working properly yet?
Looking at your data @tkzz , it does look like Radon is a bit high (200 bq/m3 is the CA threshold), but your CO2 is pretty low for a house with no ventilation. This means that either it's a large house with low occupancy or it's pretty leaky :-)
A few questions:
1. Where is the AirThings sensor located?
2. How many floors and square footage?
3. Occupancy?
If your home is in the leaky category, you'd be better off with Radon mitigation first as you'll just end up over ventilating to reduce radon. Over ventilation in TO over winter will drop your interior humidity to uncomfortable levels, and also result in unnecessary heat loss via the exchanger.
Thank you Dennis! It is on the larger side considering the # of occupants which might be the reason...
1. AirThings is in the basement bedroom on a nightstand
2. It's a 2 storey house with a basement, approx 700 sqft per floor (it's basically a big cube)
3. 2 adults and 1 child mostly, sometimes inlaws stay over.
I got a blower door test last November. The result was 4 ACH @ 50 Pa.
I think you're a bit on threshold there. If the bedroom basement is in use, then I'd be leaning towards radon mitigation first. The CO2 levels never get much above 1000 which suggests that the house at 4 ACH is ventilating itself. The VOC average is also not so high but there is a day there where it's over 500 for most of the day.
Do you have a longer term radon average? Convention suggests 2-3 months to establish an average. In my own testing here, on a similar structure, but tighter, it takes quite a high volume of ventilation to make any difference on radon, and it's slow to react. My radon level average though in the basement is about 145 bq/m3 and never gets as high as you're seeing there, about 320 bq/m3.
If you plan on doing more air sealing/renovating, then I'd think about an ERV, however in your position (and with that limited AQ data) I'd be starting with the radon mitigation as the system is pretty simple and relatively inexpensive. Hope that helps :-)
Thanks again Dennis!
I’m leaning towards the radon mitigation now… I originally thought the ERV would be a way of dealing with several things at once but now it seems like radon needs a targeted solution and it is my biggest concern . The basement bedroom does get used although not every night. I noticed that radon numbers on the top floor aren’t much better (200s when basement is 300s).
I did an alpha track 90 day test last winter (Dec - Feb) in the same basement location and it came back at 148 Bq/m3… not sure why the higher numbers now with the Airthings but this could be a November thing or just annual differences?
Wonder what are some of the key things to look for when hiring a radon mitigation company. I am talking to “Canada Radon” and they seem professional so far.
I think any proper radon remediation will cost more than installing and ERV without any of the air quality benefits.
You don't need anything fancy for the ERV, I would duct the fresh air supply into the return of the air handler and the stale air pickup somewhere low in the basement. If easy, you can also T off the stale air and add a pickup in the bathroom as well. Make sure to spec an auto balance ERV as a regular unit will get unbalanced as your air handler cycles in this type of configuration.
Heck, I know they are not efficient, but one of the panasonic whispercomfort spot ERVs in the basement might do the trick without needing any ducting.
I kind of wish this was true because I'd rather have an ERV than a radon fan... I was looking at the Panasonic intellibalance. But I'm just not sure I'll get the best radon reduction results...
Cost is a factor but not the most important factor.
I would consider doing both
I hear what you are saying Akos, but the spot ERV will likely make little to no difference for TKzz, at least based on the data I’ve been looking at more or less daily for the last year. With stack effect and lower basement air density, there is quite a strong tendency to pull air from the foundation, so you would have to pressurize quite aggressively to stop radon gas, and that would have undesirable mold effects etc. A radon system is pretty simple, at least to start, with a single slab penetration, exterior fan and correct ducting to the recommended exit point. I had my system programmed to ramp and stay at 110 CFM to react to radon spikes (and my stale air pickup is in the basement stairwell) but stopped doing this as it was mostly ineffective at dropping radon levels. The other problem is that ERV building penetrations will often be near ground level Several case studies have demonstrated that radon levels in upper stories can actually get worse with incorrect radon exhaust terminations.
Tk, radon levels are all over the place and tend to ramp up and down over periods up to a week with no obvious correlation to weather etc. although I’m sure atmospheric pressure etc do okay a role. August stands out in the data with higher levels than any other month in 2023. Will ventilation have an effect on radon levels? Sure, but likely far less than you would predict. I’m convinced at this point that radon mitigation by ramping ventilation is not cost effective over the longer term but rather that high radon levels and interior air quality are likely more effectively dealt with separately.
Keepin mind that @tkzz has posted an ACH of 4, and AQ data from rhe AirThings plot is looking ok, despite no mechanical ventilation.
“ The other problem is that ERV building penetrations will often be near ground level Several case studies have demonstrated that radon levels in upper stories can actually get worse with incorrect radon exhaust terminations.”
I think this would only be true with a mitigation system, as it is not exactly consistent with this study:
https://www.energy.wsu.edu/documents/AHT_Conditioned%20crawl%20spaces%5B1%5D.pdf
I would be interested to read those other studies though, do you have any links?
I also realize that there is a living space in the basement so I’m not saying a mitigation strategy is not called for like in the above study where they essentially created a negative pressure in the crawl.
Freyr, check here: https://aarst.org/proceedings/2016/Moorman_RADON_DISCHARGE_LOCATIONS_THAT_ARE_SHOWN_TO_AFFECT_INTERIOR_RADON_CONCENTRATIONS_NEGATIVE.pdf
You are correct in that they are talking radon termination, however an ERV with basement return, may also have higher radon levels and would have similar challenges to a lessor extent.
Negative pressure in a crawl space would be pretty effective I would think, as that's pretty much what a dedicated radon mitigation system would do :-)
There are reports here on GBA of ERV/HRV ventilation being added and working great for mitigation and others where this did not work at all. My own data shows limited differences varying ventilation rates and radon reduction (1905 vintage multistory) but with retrofits). I suspect there are two extremes:
1. A tight house with no previous mechanical ventilation, single story, and some slab/foundation sealing via poly etc. In this case, ERV/HRV likely works better for mitigation as radon is likely accumulating slowly without mechanical ventilation, but levels would drop fairly quickly after ventilation. It's also easier to keep a house like this at positive pressure, although that would be problematic for other reasons.
2. A leaky house with high stack effect (multistory) and older slab/foundation with many leak points. In that case, I suspect radon mitigation expectations via ERV/HRV would be waste of time and better resolved with sub slab depressurisation (as in a dedicated radon vent system).
Thanks guys, there's lots to think about here. My house is multistory and older (1966) so it sounds like sub slab depressurisation is the way to go for radon. On the other hand I could take a stab with the ERV which will improve Co2 and stale air and see how much radon it removes. Worst case I follow up with the radon mitigation system... I'd love to avoid buying two systems if possible. But I suppose my Co2 isn't so bad that if I just installed a radon mitigation system I could be good.
@tkzz, I would never recommend against proper ventilation, so an ERV is a great idea. You are already ahead of the game by monitoring and taking action on what you see.
In your case, if you had the budget for only one option, I would go with radon mitigation first. Having both an ERV and a basic radon mitigation setup in place gives you plenty of options, particularly if you plan on further air sealing and/or retrofits.
Sounds good, thanks Dennis! I am waiting for some quotes but I think I'll likely start with radon without closing the door on a future ERV.
Regarding radon subslab depressurization, the footprint of my house is about 700 sqft and the basement goes down about 7 feet below grade. Soil is clay. Do you think I'll need multiple extraction holes? I'm looking around my basement scratching my head wondering how multiple pipes would work. There is a part of the utility room that is roughly in the middle of the house so I'm sorta hoping this could be a one & done location.
On the extraction/location question, this is where an experienced installer in your area will be worth the investment to assess the foundation’s condition, and what will be required to mitigate. If you have a sump, that is where they would start, particularly if weeping tile is tied into it.
Hey Dennis and Akos, Just getting back to say that of the 3 radon companies, only one showed up and quoted, and he was not a certified mitigation contractor and said he doesn’t do the tests that the others apparently do.
Luckily I’m not in a rush but it does make me think about whether I should try the ERV first, and see what impact it has, worst case it will freshen up the air in my house. I could then follow up with a radon mitigation system if I eventually get quotes from the radon specialists.
How would you set up a central ERV for maximum impact when using the simplified method with a central hvac system? My house is basically a cube - 2 storey plus basement, 700 sqft per floor. There are 7 vents upstairs, 6 vents on the main and 5 in the basement. There’s one central return on each floor. System has a low static pressure around 0.2 in wc and pushes 700 cfm on max, and around 600 cfm on low.
Radon levels are typically higher in the basement, so if you want to set up an ERV for max effectiveness, I would suggest setting up the ERV stale air intake as close as possible to your basement HVAC return (or at the floor in your basement), and then dump fresh air into your supply at the furnace for distribution to all three floors. I'd also try and get max separation on the outside hoods, keeping the fresh air intake "upstream" of the exhaust with respect to prevailing winds. It's worth a try, but again based on your house type and situation, keep your expectations for radon mitigation in check :-)
The Intelibalance 100 allows you to set different CFMs for exhaust and fresh air supply so you can slightly positively pressurize your home with fresh air. This should have a positive (good) effect on how much radon is allowed in.