# How do I compare indoor and outdoor relative humidity levels?

If my inside relative humidity level is 50% at 73 F,
and my outside relative humidity level is 97% at 36 F,
how can I tell if I open my door, whether I will lose inside humidity into the atmosphere?

The real life scenario is that my wife complained that the humidity was too low in the house overnight.
I boosted humidity up last night. A LOT.

But then my wife opens both doors this morning upon waking. This is unusual for her. We have several days of rain imminent, as you can see by the above data. My cheap relative humidity dial is showing a slight decrease after 30 minutes of having the inside doors open. The screen doors with their winter coverings of removable glass panels are still in place. A significant heat transfer is occurring through the cracks around the screen doors because of the difference in temperature. But I'm left wondering if my night time humidity is going out the door as well? And is it a significant loss of humidity? Am I losing relative humidity faster than I'm losing heat?? Or maybe humidity doesn't "flow" as fast as heat. I know when it's January in Minnesota, heat flows quite quickly if we open the door!

Thanks,

## Answers and Replies

Seems to me you first need to calculate the amount of water per unit volume of air (g/l) for each condition of temperature and RH to arrive at any rational conclusions.

Thanks for the tip.

I have amount of water per weight of air. I found a calculator online that told me that outside I had 4.67 grams of water per kg of air. And if I were to import this air into my home, I'd be looking at a RH of 27%. That explains why I had a loss of RH in my house. The RH indicator is fairly close to one of the open doors. So the increased humidity overnight was flowing out the door.

I'm curious to know if humidity flows as fast as heat. I'll start by looking for "humidity exchanged across a gradient." I'm currently reading the Wikipedia article on humidity.