What Should Humidity Be In House In Winter? (30%-60% or 35%-45%)

Maintaining a stable and sensible indoor humidity levels in your house in winter has all sorts of positive effects. That’s why we can set a humidifier to a specific relative humidity percentage. The key question here is this:

What Should Indoor Humidity Be In Winter?

If you set the humidity levels to a too high percentage (more than 60%), you will risk mold infection. If you set the humidity to a too low percentage (below 30%), you can experience the negative effects of air being too dry.

So what is the optimum percentage what should inside humidity be in winter? 60% is too high. 30% is too low. Anything between 30% and 60% is OK.

That precise sweet spot for what should humidity be in your house in the winter is between 35% and 45%.

What Should Humidity Be In House In Winter humidity sensor

Many of you have asked what happens in the winter and in the summer. Something along the lines of:

  • What to set humidifier at in winter? That’s usually a question for furnace humidifier setting or a stand-alone humidifier setting.
  • What should you set your humidifier at in the summer? That is primarily for a stand-alone humidifier setting.

It’s important to have an idea of what indoor humidity levels mean; we’ll first have a look at that. Then we’ll look if there is a difference in what should indoor humidity be in the winter vs. in the summer:

What Does ‘Indoor Humidity Level’ Mean?

Humidifiers basically enable us to increase the amount of water in indoor air. In theory, you can set it anywhere between 0% and 100%. What does that actually mean?

Well, at any given temperature (and pressure), there can be a maximum amount of water vapor in the air. That’s a 100% relative humidity level setting. Neither 0% nor 100% is what you should inside humidity be in the winter or in the summer for that matter.

For example, at 68°F air can hold up to 0.00107 pounds of water per cubic foot (100% saturation). In a 12×12 room with an 8 ft ceiling, you have 1152 ft3 of air. At 100% relative humidity, the total amount of water in the air is 1.23 lbs or 0.33 gallons of water.

At 0% relative humidity, there are 0 gallons of water in the air.

Similarly, we can calculate how much water is in the air at 10%, 20%, 30%, 40%, 50%, and so on humidity setting. Just to illustrate, here are the air water content figures for this example:

Indoor Humidity Levels (%) Amount Of Water In The Air (Gallons)
0% 0 Gallons
10% 0.033 Gallons
20% 0.066 Gallons
30% 0.100 Gallons
40% 0.133 Gallons
50% 0.166 Gallons
60% 0.200 Gallons
70% 0.233 Gallons
80% 0.266 Gallons
90% 0.300 Gallons
100% 0.333 Gallons

Now, here is what the humidifier does. Let’s say you have 30% humidity levels in a room and you want to raise humidity levels to 40%.

At 30%, the total amount of water in the air is about 0.100 gallons. At 40%, the total amount of water in the air should be about 0.133 gallons.

When you set a humidifier to 40% in this case, the humidifier will have to output 0.033 gallons of water. This will adequately increase the humidity levels to the humidifier set value. That brings the humidity to what the humidity levels should be inside your house in the winter.

What Should The Humidity Be In Your House In The Winter VS Summer?

There is a lot of discussions in terms of what is an ideal indoor humidity in winter and in the summer.

Truth be told, the humidifier relative percentage setting should be the same in the winter and in the summer.

Target for that 35% to 45% sweet spot.

There is no reason why the humidity settings should be higher in the winter vs. the summer.

Some speculate that indoor air with higher water vapor content is more difficult to heat. That is completely true; air at 40% relative humidity level is harder to heat than air at 30% relative humidity level. This is due to differences in specific heat capacity (measured in Joules per kilogram per degree).

Water has a specific heat capacity of 4,200 J/kg°C and dry air has a specific heat capacity of 1.012 J/kg°C. Indoor air is a mixture of mostly air and some water; if you have more water, that air will be harder to heat.

However, here is the key point:

The difference in specific heat capacity of 30% vs 40% relative humidity levels air is insignificant. You won’t have more than $10 on electric bills during the winter just because you have a lower humidifier setting on your furnace humidifier.

The appropriate and adequate way to set your humidifier is simple:

Just stick to 35%, 40%, or 45% year-round.

Hope this helps.

2 thoughts on “What Should Humidity Be In House In Winter? (30%-60% or 35%-45%)”

  1. In summer we open the windows, if you dont use air conditioning equipment.So its almost impossibe to go lower than 45% with a deshumidifier running 24/7 in a humid part of the country.

    Reply
    • Hello Roberts, that’s right, with open windows, there is a constant supply of humid air. The low relative humidity air (generated by a dehumidifier) escapes and is replaced by humid air again. When using a dehumidifier, it makes sense to close the windows.

      Reply

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