Comments on: Does a Gas Furnace Dry Out the Air in Your Home?

By: Charles nall

Charles nall — Fri, 23 May 2014 03:12:52 +0000

If you have gas furnace does
If you have gas furnace does your run off gas's also

By: C. R. James

C. R. James — Fri, 24 Jan 2014 04:03:28 +0000

Seeking a way to get my 30
Seeking a way to get my 30'x30' addition with cathedral ceilings to not rain down condensation from the T&G; pine plank ceiling during outside temperature shifts. I have Buderus condensing gas boiler, radiant heat above the floor sheathing under click-lock bamboo and Porcelain tile. Ceiling is truss with blueboard at innermost surface with sprayfoam over the Blueboard to completely seal the ceiling from the outside.
Water drips down at times through the butt ends of the pine planking and where the interior vertical walls of sheetrock meet the interior pine planking.Drives us nuts! Have suggestions of air exchanger(s), but can't get any solid reliable info as to how to solve it once and for all. Have moisture at window sills, and at double hung window upper and lower sections throughout old section of house and new. Have 33-34% humidity currently at 65degreesF in new kitchen/DRm. at 10BELOW zero outside temp currently.
HELP, what to do?
Thanks. In VT.

By: Allison Bailes

Allison Bailes — Wed, 22 Jan 2014 17:33:01 +0000

Paul R.:
Paul R.: No and no. I don't know what the factors would be or studies about RH and ventilation rates. I can tell you about my experience with the latter, though. In the house that I built, I installed a 120 cfm HRV. This was back when I knew next to nothing about the issue, and the contractor who installed the system didn't know much more than that. So I ran it continuously the first year, and had horribly low RH. Wood shrank and popped. The next winter I throttled it down to less than 50 cfm and the conditions were much better. Wish I'd had dataloggers installed to show you the data.

Tom D.: Indeed, tight homes can be too humid even in winter. Spot ventilation can help, as can using an HRV instead of an ERV.

Andrew D.: It doesn't really matter what size the furnace is. A larger furnace should give you the same temperature rise but do it with a larger air flow. And as long as you're still keeping the house at 70° F, that air still gets mixed with the rest of the house air to give you about the same conditions as with the smaller furnace. What happens, though, is what Bob said. You get short blasts of hot air, followed by periods of cooling, so when the furnace is running, it might feel drier.

Bob: It shouldn't make much difference in the RH at all.

By: Bob

Bob — Fri, 17 Jan 2014 03:09:22 +0000

Andrew Dunn oversized
Andrew Dunn oversized furnaces definitely contribute to the "scorched air" feeling of gas heat due to the hot blast of heat for a few minutes followed by long periods of no heat. Not sure how much humidity difference it makes though.

By: Andrew Dunn

Andrew Dunn — Thu, 16 Jan 2014 23:58:14 +0000

I am curious if you think
I am curious if you think that a very oversized gas furnace for example a 2 to 3 times oversized unit could overheat and dry out the air. If the unit provides 2 to 3 times as much heat energy to the heat exchanger over the same period of time, airflow, and duct size, wouldn't the supply air cycle back into the home feel dryer? This example could apply to a sealed combustion 2 to 3 times oversized furnace.
In either case (open combustion or closed combustion) with a correctly sized gas furnace the airflow would match the heat energy provided at the heat exchanger closely enough to maintain a steady relative humidity, rather than dry air cycled back on the supply side.
I am not disputing the reasons you gave above, however wanted to seek clarity as it seems an oversized gas furnace can dry out the air even in a tight home.
Thanks for your feedback.

By: Paul Raymer

Paul Raymer — Thu, 16 Jan 2014 19:15:01 +0000

I frequently get this
I frequently get this question as well although it it is more in regard to what is affectionately known as a "scorched air" distribution system rather than the furnace itself! Interesting thought to "Make sure you have control of your ventilation system, though, and experiment with the ventilation rate." We can make ventilation system controls that do pretty much anything like vary the rate automatically in response to other factors, but what would those factors be and would anyone be willing to pay for such controls? Do you know of any data that would tell us the percentage of impact from the mechanical ventilation on the RH in the house?