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Ways to reduce condensation on windows

3 replies [Last post]
Joined: May 8 2003

When I get up every morning, I notice that there are lots of condensation on the windows. I would like to know if any of you have recommendation in reducing the amount of condensation that occurs. I know this is strictly physics, but are there any tricks that any of you like to share.

I guess one trick is to leave the temperature inside the house at the same temperature as the outside, but I don't think I like to wake up to a 40 degree house. :)

- J

Joined: Apr 2 2003

I'll offer a couple of thoughts while you wait for those with more knowledge or experience to apply.

Since condensation results from warm moist air hitting a colder hard (non-absorbent) surface, you can attack the problem from either or both ends.

To reduce warm, wet air:
- consider spacing morning showers
- installing a bathroom fan
- installing openable skylights
- using lids when you cook
- using kitchen fan when you cook

To limit colder hard surface:
- use window coverings (though open on a regular basis so what warm air does penetrate, does not get trapped)
- run your home a little cooler than you might otherwise when it is especially cold outside to minimize the temperature differential
- obviously, if you have the option to replace some of the single pane with double-pane, consider that.

I'm sure others will have suggestions/comments.


P.S. In our case, we never had a problem even with no draperies because there are only 2 of us. We did space our showers slightly (1/2 hour), did open a window. However, in anticipation of those times when there are more visitors in the house, we eventually installed a fan and changed out the singlepane glass to doublepane. This month, I will pick up openable skylights as well

eichfan at rawbw dot com

Joined: Mar 20 2003

One important thing to do is to regularly exchange the moist air in the house with fresh dry air from the outside. One should keep in mind that the air's moisture capacity increases with temperature. So even relatively moist cold air that comes into the house will become dry when it warmes up.
Of course too much venting might increase your heating bill. Someone on this board installed a pretty sophisticated automatic ventilation system with a heat exchange which keeps the heat inside while getting the humidity out. But that is optional.
Studies have shown that it is more efficient to vent repetedly for a few minutes compared to having a window a little bit open for the whole day. This is because a lot of the heat in a room is stored in the floor, the walls, the furniture etc. So if you open the sliders fully for a few minutes, you will have exchanged most of the humid air, but the room will regain it's temparature quickly due to the stored heat.

Hope that helps

Joined: Mar 20 2003

That was me who installed a Heat Recovery Ventilator on my home under my foam roof. You can read about it on the last page of the recent Eichler Newsletter snail-mailer (Fall 2003). All new buildings in Washington and Canada and more states to come will require one per code. We are very happy with it and it surprised us since we ended up keeping it on all summer too. Here is more information about it:

I will add some additional suggestions to the previous posts:

- Get a dehumdifier and try to keep the indoor humidity under 50%. You can purchase a stand alone unit at Sears.
- Get a hygrometer at the hardware store and check your indoor humidity. If it gets above 50%, turn the fans on (or open a a window if you don't mind the cold).
- Anything against a cold surface (i.e. drapes, furniture, etc.) will cause more condensation- even on walls which can be bad news (mold now has food to grow- it won't grow on glass). Remove anything close to the surface that is getting the condensation.
- Install bathroom fans. Put the fans on a timer. It is suggested to run the timer for a full hour after bathing. You can also use the fan to lower the humidity of your house if you need to (although you can see the trade off in heating the air then immediately removing it- thus the advantage of an HRV). Be sure to size it correctly. Research shows that fans that are too noisy or powerful (too breazy) will not be used by the occupants.
- Run your kitchen fan or if you remodel, be sure to include one in your kitchen that is a hood directly over your stove. It can be tough in an Eichler to shoe-horn a hood into the design but it can be done (I'm planning to do it for my kitchen remodel).
- Add double pane windows, wall, and roof insulation.

When we (Eichler owners) upgrade, we remove the "random" ventilation and we need to bring in more formal ventilation (ie. fans, HRV's). Condensation is a bigger problem as the number of occupants increase. It's absolutely the right thing to insulate your home but you need to "insulate but don't forget to ventilate".


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