Vented dryer depressurization and its effects on radon levels?
calum_wilde
| Posted in Mechanicals on
Has anyone studied the effects on radon levels caused by running a dryer, or other unbalanced ventilation equipment, in a well sealed home?
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Unless you take in laundry from the neighbors, there's no way running the dryer could make much difference in radon levels.
Running my hrv 24/7 at the normal setting, 72 cfm, makes a significant difference in radon levels, as does opening the windows, which reduces the level from around 4 to less than 1.
I have an electronic radon monitor so I can see the effect. But running ventilation only occasionally makes little difference. I usually don't run the hrv this time of year. But if I close all the windows and forget to turn on the hrv, radon levels rise significantly.
Obviously, reducing radon levels with a radon mitigation system is a better idea if you don't plan on constant ventilation. And the energy cost of running a bathroom fan all the time may be a consideration.
I would NEVER, EVER have a house with negative pressure. Not only the dryer, but bathroom fans and kitchen exhaust fans, all running at once, can create havoc with your indoor air quality (IAQ), specially if you know you have Radon.
I would start with radon mitigation solutions. Installing ERVs/HRVs or supply-only ventilation without fixing the radon problem is just putting a band-aid. Once you mitigate the radon, look for supply-only or balanced ventilation solutions to achieve IAQ. I prefer balanced ventilation with ERVs, and we run them 24/7.
Armando,
I have an HRV that running constantly. The only unbalanced ventilation is the exhaust only dryer. My house has an ach50 of 1.0. The dryer is likely pulling a measureable negative pressure on the house.
I'd love to be able to make the dryer a balanced system, but dryers just aren't designed for it. Ventless dryers are still prohibitively expensive at $1700 CAD for a family size. I'm still shopping though.
A dryer wouldn't be much different from exhaust-only ventilation, except that it would run a lot less. The usual advice is that exhaust-only ventilation will draw in enough real outside air that the net effect on radon will be to reduce it, but I think that how that works out would depend a lot of the particulars--you could come up with scenarios that go both ways. And I think I've seen anecdotes here on GBA going both ways.
If the ventless dryer you are looking at is a heat pump dryer, it also offers much lower energy consumption.
But you can also crack a window open when you run the dryer if you are concerned. I would not be concerned.
Say one had a sub-slab radon mitigation system. That should be hundreds of pascals vs ~5 pascals caused by the dryer.
A radon mitigation system may also move enough CFM that one doesn't need to run a HRV (with all interior doors open).
@Stephen S - do you notice that on windy days or temperatures with large stack effect that radon level is low even without the HRV?
With the HRV running constantly the lowest impedance source of make-up air for the dryer will be the HRV system, not seepage through the slab or foundation walls, and the amount of depressurization of the house from the dryer would be tiny.
A typical residential dryer is running less than 10% of the time, so even if there were substantial depressurization, the other 90%+ of the time the HRV would be constantly diluting whatever had been picked up during the operation of the dryer.
Jon R. My house is tight enough (.59ach/50) that I don't see any evidence of a stack effect. Plus it's a one level house on a slab.
And I always run the hrv unless the windows are open.
That said, radon levels do vary quite a bit, even with windows closed and hrv on. The levels don't seem to correlate with weather as far as I can tell.
Calum,
Q. "Has anyone studied the effects on radon levels caused by running a dryer, or other unbalanced ventilation equipment, in a well sealed home?"
A. Yes. For more information, see Exhaust-Only Ventilation Systems and Radon.