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Could an 80% gas furnace pull radon into the home?

I own a 1930 duplex in Portland, OR and am starting to do gradual updates. The first thing I will be doing is decommissioning the in ground oil tanks and installing gas furnaces. I am trying to choose whether to do 80% furnaces or 90% furnaces and am weighing the following thoughts:

1 – There is a radon mitigation system under the basement slab and a couple of cracks in the slab. Since an 80% furnace would use atmospheric combustion would it be able to depressurize the building enough to potentially bring radon into the basement? The original radon test, I believe, was done in the summer when the current furnace would not have been running.

2 - In "All About Furnaces and Duct Systems" posted by Martin Holladay on 1/24/14, Martin talks about low thermostat set points leading to corrosion of the heat exchangers in condensing furnaces. Since these furnaces will be in rentals and I won’t be able to control the thermostats, I’m hesitant to put in condensing units due to the potential added maintenance/replacement.

Are these real reasons for concerns? I would appreciate any input that folks would have.

Thanks,

Cyrus Collins

Asked by Cyrus Collins
Posted Tue, 02/18/2014 - 16:10

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3 Answers

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Cyrus,
You didn't tell us whether you have an active radon mitigation system or a passive system. If the system is active (with a fan), the furnace won't affect your radon levels.

Regardless of what type of radon mitigation system you have, you should caulk the cracks in your slab with a high-quality caulk.

Once your cracks are caulked, I wouldn't worry about the effect of at atmospherically vented furnace on your radon levels.

It seems unlikely that your tenants will turn down their thermostats so low that you'll have to worry about condensation in your heat exchanger. But if that thought worries you, buy an 80% AFUE furnace.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 02/18/2014 - 18:26

2.
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Thanks Martin,

The radon system is active, so I won't worry about that. As far as the condensation in the heat exchanger, I haven't been able to find much information about how common that is.

Answered by Cyrus Collins
Posted Tue, 02/18/2014 - 18:41

3.
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Condensation in the heat exchangers is pretty common in vacation homes in New England where they might set the room thermostats to 45-50F or something as freeze-protection for the plumbing, but rare for fully occupied homes.

Hardy folks who prefer spending the money on sweaters than heating bills might keep a rented home that cool, but even passive solar ("bright clouds") gains at Portland OR's mid-winter temps would likely keep the house warm enough for THEM, no need to run the furnace, eh? ;-)

Answered by Dana Dorsett
Posted Wed, 02/19/2014 - 17:45

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