Comments on: What Is the Best Indoor Relative Humidity in Winter?

By: David Butler

David Butler — Sun, 15 May 2016 21:57:34 +0000

@Pohl, the body responds to
@Pohl, the body responds to relative humidity, not so much to absolute humidity. So while 10-15C is indeed a comfortable dew point range indoors, that’s only true because 10-15 correlates with the comfort range for relative humidity.

Consider when you’re outdoors and it’s 35C… a dew point of 23 or even 25C will feel very nice.

Likewise, mold responds to relative humidity, not absolute humidity.

Absolute humidity is a useful metric where you have an imperfect boundary between air at different conditions, such as ventilation, infiltration and vapor drive.

By: pohl Zoltan

pohl Zoltan — Sun, 15 May 2016 10:15:32 +0000

Hi guys
Hi guys I think that RH doesn't tell us how comfortable we live indoor. The RH is as the name said "relative" and show us a percentage of water vapor in a mass of air reported to the max amount of water vapour that mass could contain. It doesn't tell us the amount gr/m3 or gr/kg in the air. We could have at different temperatures different RH. Isn't it? As we heat up the air the RH will decrease. But the Quantity of moisture gr/ m3 remain the same. The absolute quantity of moisture will tell us the real absolute quantity of moisture into the air, that is Dew Point an not RH. Leet say in a summer morning we have outside 21C and RH 100% and DP 21C. It means that the air is saturated and we will see dew on the grass. During the day the air will worm up to 32C and RH 50% at the same DP of 21C. During the day even if we have the fantastic 50% RH as everybody tells is the optimum. At DP of 21C the air is very humid. The comfortable limits is between 10-15C DP. Am I right? In this case presented we have to humidify, ventilate etc our house according to DP and not RH.

By: David Butler

David Butler — Fri, 22 Jan 2016 02:05:04 +0000

In reply to Alejandro Martinez. @Alejandro, in addition to
@Alejandro, in addition to what Allison said, an ERV can in some cases RAISE RH in winter, if used as primary exhaust for a high use shower. This is most likely to occur during shoulder months when weather can oscillate between periods of rain mild temperatures and cold snaps. In warm climates, ERV's are most useful for reducing ventilation-induced moisture in summer.

By: Jerome Lisuzzo

Jerome Lisuzzo — Thu, 21 Jan 2016 19:08:58 +0000

Thanks for another great
Thanks for another great article, Allison. My wife and I live in a Passive House in West Chester, PA (about 20 miles west of downtown Philly). At the moment, our interior stats are 69 degrees and 39.3% RH. Outside, it's 25 degrees and 88% RH. Although we seem to be at the upper limit of what is generally considered acceptable, that feels very comfortable. In the past, those numbers would have caused me to keep our ERV set to low except when showering. But I now understand why we should also be increasing the ventilation when we're engaged in other moisture producing activities like cooking or washing clothes.

By: Jeremy

Jeremy — Thu, 21 Jan 2016 18:08:36 +0000

We're in NE Ohio and keep the
We're in NE Ohio and keep the humidity around 32% in the winter. No static at all. Last winter when it hit -5 air temp we had a little frost on the inside corner of an addition, I backed the humidity down to 10% while it was that cold. All that started me on a major air sealing of the house and adding R70 to the attic, which is mostly but not completely done.

By: Sean Lintow Sr

Sean Lintow Sr — Thu, 21 Jan 2016 06:59:14 +0000

Well I will stick with around
Well I will stick with around 25%-40% for most of us in colder climates with slightly cooler temps http://thehtrc.com/2015/faq-window-wall-condensation-iced

Interesting that you are getting northern lights at 35%, generally as recall it shouldn’t be happening until you are in the teens to maybe low 20’s

As for when living down south, I might say 30 to 40.

By: Allison Bailes

Allison Bailes — Wed, 20 Jan 2016 22:42:47 +0000

In reply to Gerald McClain. Gerald, I'm surprised you don
Gerald, I'm surprised you don't get static electricity at 25% RH. I get it at about 35% in my condo. Regarding your question about whether you should get a humidifier, I'd say if it ain't broke, don't break it. If you're comfortable and don't notice a static electricity or dry skin problem, why rock the boat? The ideal summer humidity is a different animal. Up to 60% is fine then. If you're getting 50%, that's great.

By: Gerald McClain

Gerald McClain — Wed, 20 Jan 2016 22:21:49 +0000

I have a ground source heat
I have a ground source heat pump system and the humidity is shown to be 25% when outside temperature is about 25 degrees. I do not have any static electricity when turning on lights or touching metal objects I live in Oklahoma in a 6,000 SF home keeping the temperature constant at 71 degrees night and day. My average cost for the total electric home is $156 per month for cooking, lights, heating, cooling and hot water. I have 6 boreholes 300' deep with 1" HDPE pipe, reverse return and 3 units 4 ton, 3 ton and 2 ton units with each on its own thermostats. i have no outside units making noise and the inside units sound like refrigerators when running. Home was built is 2010. Should I get a humidifier to increase humidity in the home? It is very comfortable. In the summer time when it is 100 degrees outside the humidity is usually around 50%. It is very comfortable even at 50% humidity.

By: Allison Bailes

Allison Bailes — Wed, 20 Jan 2016 22:12:30 +0000

In reply to Nate Adams. Good questions, Nate. Most
Good questions, Nate. Most people keep their homes around 70° F, and that's what I assumed here. For those who keep it significantly cooler indoors, the chances of accidental dehumidification are greater because the surfaces are cooler. In summer, a dew point of 55° F is what you get at 75° F and 50% RH. In winter, you get 45° F with indoor conditions of 70° F and 40% RH.

By: Nate Adams

Nate Adams — Wed, 20 Jan 2016 22:06:05 +0000

Great article! I've been
Great article! I've been thinking about this subject as my house runs in the teens of RH. What temp are you assuming for RH again? Would dew point be good to add as well?