Heating vs dehumidifying - what is more energy efficient?


it got cold in my part of the world now, so I had to start heating.
But of course I want to keep heating cost down so I tried only heating my bedroom and my living room gets down to 15C/59F and I get condensation on my windows.

So I looked at all my devices and found the humidity and temp sensors, and indeed my cold living room gets humidity levels beyond 70% which is good for mold.

So I was wondering what is more efficient? Permanently heating or a dehumidifier?
There is probably an argument for doing both since dryer air can be heated more efficiently.

Has someone compared the energy use of those two methods?

And, depending on the type of dehumidifier you have, warmer air can be dehumidified more efiiciently. Many refrigerant-based dehumidifiers struggle at temperatures below 60F and may be damaged if they don’t have defrost functionality.

Definitely get a good dehumidifier and set it to 40% relative humidity. That gives you a buffer for all of the water vapour you are constantly adding by breathing.

I don’t have any data on the energy usage of one versus the other, and I also suspect that you need to deal with both issues. I’d suggest dealing with the humidity issue first since you really don’t want to have mold in your home. Side benefits of a dehumidifier are that they also slightly warm the air, and help circulate the air when they are running. So adjust the humidity first, and then add heat as needed. I suggest a quality dehumidifier if you can afford one. They cost more initially, but generally have better warranties and are designed to run longer, if not full-time.

I purchased an Aloair Sentinel HD55 and placed it in a closet under a stairwell and ducted it 6 feet into a closet in the basement to keep the noise level down. Place it on a stand and run the gravity drain to a condensate pump so you never need to empty the discharge water. If you’re going to control it with a smart switch make sure it restores to the powered-on state after a power outage.

Ideal indoor humidity is based on outside temperature. You can find various numbers that are recommended - the ones below are what I’m using to automate a dehumidifier in my basement.

Outdoor Temp / Ideal Indoor Humidity
50F+ / 48%
25F - 50F / 38%
0F - 25F / 36%
-20F - 0F / 30%
<-20F / 25%

I started to gather some data about the normal development of humidity and temp in my unheated room.
Its not completly conclusive so far, but its quite interesting e.g. how little the effect of intermitend ventilation is (windows fully open for 10 min, 3-4 times a day)
Also I started heating in the evening to 16C/61F and the humidity wasnt much affected it seems.

But i asked myself, what exactly I want in the end and that is save money and not have mold. the only part that is in danger of getting moldy are the window sills, if I can wick away the moisture or get one of these cheap window cleaner vaccuums, and just clean the windows of water 2x a day, that should be fine.

and btw: what would be a good data and visualization intergration for HA? havent looked much into it but collecting sensor data and being able to do correlations, means, CI/variance in some interactive graphs would be awesome.

Few notes:

  • Temperature in a room is not heterogeneous. In my experience, in cold days, temperature is significantly lower at windows. (Your mileage might vary due to different weather, different construction etc.) Sometimes, you might want just to mix the air by a fan. However, you probably don’t want to do this when you are in the room.
  • The same applies for relative humidity. Even if absolute humidity is the same in the whole room, relative humidity will differ due to the temperature differences.
  • You will probably want to keep reasonable humidity (and thus also temperature) even in places where you aren’t at the moment, because of mold risk.
  • Efficient ventilation (i.e., short and intensive, like all windows fully opened for few minutes rather than slightly opened windows for a long time) can help you to get rid of humidity without losing too much heat. (You will probably want to ventilate anyway, as you need to get rid of CO2…)

The impact of the heat source
The efficiency of dehumidification and heating will vary by your heat source. If you have electrical resistive heating (not electrical heat pumps), many electrical devices can be also an efficient heater. At the end of the day, they transform electrical energy into another, often into heat that remain in the room. Note that they don’t always spread the heat quickly in the room, but they eventually will do so. Running those devices might be as efficient as using resistive electrical heater. So, running a dehumidifier will also heat your room a bit.

If you don’t use resistive electrical heating, then using electricity is often significantly more expensive. When the dehumidifier works with low efficiency (e.g., temperature is low), it might be cheaper to run heating instead.