Heat pump water heater and increasing radon levels
Hello.
We build our house a year or so ago. We have a water heater that is an electric heat pump. We had it venting outside and unfortunately, it was creating a condensation problem with the cold air coming through the vent mixing with hot humid outdoor air. As a result, we disconnected the exhaust to the outside so now the cold air from the water heater is exhausting into the unfinished basement. This type of set up is allowed per code. However, ever since we made this adjustment, our radon levels have been increasing. They used to be below 1. And now they range between 2-3. It is very clear that this changed caused the levels to increase. I have no idea why and I have no idea how to fix one problem without causing another problem. Has anyone seen or heard of this? Any suggestions?
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Before it was venting air out of the basement continuously, it makes perfect sense that your radon levels would rise as a result.
What kind of climate are you in? I'm trying hard to think of a climate where venting the water heater to the exterior is better than venting into the house. The air that you exhaust is replaced by outside air. Unless the outside air is at room temperature the exhaust air is better than outside air.
I'm by no means an expert on radon, but I think the way it's dealt with is by having a fan that exhausts it to the exterior. The key is that it doesn't pull air from the basement, which is part of the conditioned air of the house, but instead pulls it from under the basement floor. Sometimes you don't even need a fan, just vent pipe will do. Part of the solution is sealing your foundation as tight as you can -- paint will work -- to keep radon from penetrating.
Thanks for your response. We live in Chicago. Cold winters.
You want to vent to the inside. When you vent to the outside you're trading the vent air for an equivalent volume of outside air that's leaking into your house. So if it's 20F outside you're trading maybe 50F air for 20F air, cooling your house.
Does your basement have a sump pump or interior perimeter drains? Sometimes you can use them to pull air from under the slab and vent radon.
My first thought is you should be venting outside, and drawing from the outside (two separate ducts).
Thus, no negative or positive pressure for the basement. Positive air pressure is wafting radon through cracks into the home. Negative air pressure is stealing conditioned heated air from your living space.
Could you send pictures of your outside vent, describe the problems in more detail? Perhaps some sort of baffle could spread the exhaust air over enough area to low the problems.
Or replace the HPWH with an external unit, like the SanCO2 split system. Then you have no change to your basement airflow (and are of course free to put a radon system or not in as needed).
The water heater itself is not increasing your radon levels, what was happening is that when the water heater was exhausting outside, it was acting as an exhaust fan, blowing some of the radon out of the house. New outdoor air was drawn in through every little gap, crack, and leak in the house, so you were running a sort of unintentional radon exhaust system. Now that your water heater is exhausting into the indoor space, it's just recirculating indoor air, so radon levels are going to build up to wherever they would have naturally stabilized before if the water heater wasn't running and exhausting air to the outdoors.
The usual way to deal with elevated radon levels is to seal the foundation and put in some perforated pipe with a fan running a constant negative pressure *behind* the sealed area (i.e. between the sealed indoor area and the underground area outside of the sealed off indoor area). This makes sure the radon is exhausted through the radon system and doesn't make it's way into the indoor air. This type of system doesn't pull air from the indoors, either, so it shouldn't impact your heating costs much, if any.
Bill
2-3 pCi/L is below the EPA limit of 4, but 4 is not a magic number, so it's smart to keep the radon lower if possible. I would not rely on my water heater for radon control; I would get a certified radon mitigation professional to design and install a system.
I agree, and the fact that the levels were lower with the small amount of air being exhausted previously by the water heater shows that a basic, proper, radon mitigation system will be able to get those indoor radon levels down.
Bill