Claim: Interior humidity makes heating more efficient?
I came across a claim that humid air ‘holds more heat’ and therefore makes heating more efficient (e.g. furnace will run less often).
Here is a link to a page that makes a similar claim: https://www.griffithenergyservices.com/articles/humidity-affects-home-manage#:~:text=Humid%20air%20holds%20heat%20more,to%20continually%20replenish%20indoor%20heat.&text=Balanced%20humidity%20also%20safeguards%20your%20indoor%20air%20quality.
This feels like classic misconstruction of the basic science, but maybe I am missing something. Is this a ‘thermal mass’ claim, which I can only imagine would be beyond negligible; or is it something else?
Obviously there are reasons we want RH to be within a certain range for comfort and condensation issues, etc. but heating efficiency?
Thoughts?
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Here's a Physics Stack Exchange which seems to get at this issue: https://physics.stackexchange.com/questions/45349/how-air-humidity-affects-how-much-time-is-needed-for-heating-the-air
Without reading the entire article (I just skimmed it), what they are saying is basically true. In air conditioning terms, which might be easier to understand, it works like this:
Cooling dry air uses the "sensible" heat removal rating of the air conditioner. It's easier (uses less energy) to cool air like this. All of the work of the air conditioner is going into lowering the temperature of the air.
Cooling moist (humid) air uses the "latent" heat removal rating of the air conditioner. This uses more energy, because a portion of the work done by the air conditioner is going towards condensing moisture out of the air -- dehumidifying the air -- so not all of the work is going into only lowering the temperature of the air.
With heating, it works in reverse, although you're not typically adding moisture with your furnace, you would need a humidifier to do that. Moist air DOES hold more energy, but I wouldn't consider that to be "more efficient". Moist air DOES "feel" warmer though, because of how your body feels enviornmental conditions, the same way dry air "feels" cooler in the summer compared to a humid day. Keeping humidity levels reasonable DOES make a home more comfortable, and IS better for your health compared to an excessively dry home.
Too much humidity can be an issue for mold growth though, so you don't want to overdo it. Regarding humid air holding more heat, while basically true, it doesn't really do anything for efficiency. Your furnace in the winter is putting in enough heat to cancel out the thermal losses through the structure to maintain your setpoint temperature inside. It doesn't matter how much heat is "held" inside, the losses are still the same, and your furnace still has to put in enough new energy to replace those losses. The only difference is that it will take a little longer to RAISE the temperature of moist air compared to the same amount of dry air, but once you're done raising the temperature, you're right back to the steady state conditions where you're putting in enough new energy to cancel out the losses again.
The short answer is that keeping humidity reasonable does make a home healthier and more comfortable, but it won't do anything to change how much energy you use to maintain a constant indoor air temperature, so it won't do anything to improve your home's energy efficiency.
Bill