Solving winter high humidity issues
Hi all,
I live in a new build, completed last year, and it is quite tight. So tight in fact, that in the winter (Vermont, cold and snowy), we have issues with really high humidity, in the 60-70% rage. This manifests as condensation on our windows when temperatures drop, which over the course of the season results in mold.
We have an ERV, and my hypothesis is that because it retains moisture, there’s no effective way for us to reduce humidity faster than we add it through showering/cooking/plants/etc… We tried a dehumidifier, but it wasn’t up to the task. We could install a whole home dehumidifier, but we don’t want to run all new ductwork throughout the house. To use the current ductwork we’d have to remove the ERV, which would mean we don’t have a balanced system anymore. We heat with in-floor radiant and an air-to-water heat pump.
I’m looking for suggestions on what a possible solution would be. Would swapping to an HRV solve the problem? Installing a wood stove? Any other ideas?
Thank you!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
High humidity in a new build would not be uncommon thru the end of the second heating season.
When it is below zero condensation on the windows is pretty normal. I mop up my windows twice a day when it is that cold.
Is the 70% January humidity number accurate? Do 3 different meters agree pretty well?
Where do you think all this moisture is coming from?
I have to ask some silly questions Got a huge aquarium, more than a dozen plants in the house, more than one living thing per thousand square feet, standing water in the basement, How many minutes does a shower run each week?
Dry the house out this winter If the ERV can’t keep the humidity under 40% then crack open a window and keep it open until the humidity is under 35%.
Walta
Agree with Walt... Identify any excessive contributors.
Are you running bath fans during showers or boosting the ERV flow? Range hood when cooking?
Crack a window if the OA dewpoint is less than inside, or during showers/cooking. Preferably mid day when solar gains are causing a net excess of heat anyways.
You can get humidity controls for the ERV to boost ventilation when indoor humidity is higher than desired. If OA dewpoint is lower than indoor the ERV will reduce humidity but at a slower rate than a HRV since it recovers some (but it won't add humidity unless the OA dewpoint is higher than indoors). Some models allow for the core to be swapped between HRV/ERV.
Also, is your temperature indoor temperature 68degF or higher? Since humidity is relative, cooler space temps will result in proportionally higher indoor relative humidity levels (absolute humidity (dewpoint) would be the same though).
Run the bathroom fan during and after the shower.
Make sure you use the stove exhaust fan every time you cook.
Buy a good dehumidifier (is the one you have a quality model?) or a second one and run them on high.
Buy another thermometer with humidity reading and see how that reads.
Keep all the windows open on nice days and get rid of any off gassing humidity from the new construction. Fresh air is good for a new house.
Thanks for the answers everyone. Yes, 70% is in January. I have four humidity sensors (five if you count the one on the dehumidifier). One in the basement, two on the main floor, and one upstairs. The basement is the driest and hovers in the low 60%, while the upstairs is the highest and hovers in the high 60's to 70%. We keep the main floor at 70 degrees - the upstairs is a bit cooler usually, thus the higher number.
I run fans when cooking and also for 30 minutes after each shower. I do have a lot of plants, which is certainly where a fair bit of humidity comes from. I'll try cracking windows this winter more often. Was hoping there might be a better way to dump humidity quickly when it does get high though!
You must get the humidity under control!
In a cold climate no wall is safe with 70% humidity!!!
the dew point is so high moist air will find something below the dewpoint and condense liquid water inside your walls. Unseen mold and rot inside your walls seems very likely to me.
If it is 68° 70% indoors that puts the dewpoint 57.8 you must have triple pain windows.
Would you care to define what you mean by “a lot” of plants?
I think you are going to have a window open a few inches most of the winter to dry the place out.
Walta
Maybe some more details on the construction would be helpful?
What sort of dehumidifier did you try was it a newer model with a capacity of at least 35-40 pints/day? I would be surprised if a 70 pint per day couldn't manage things. Try some different locations around the house. A dehumidifier has the advantage that it's essentially a heat pump, your getting some waste heat from the process (not sure what the effective COP would be though).
You're dumping a lot of water into the air watering all those plants. It's no wonder your windows are fogging up. After the plants drink all that water, where do you think it goes?
I think you're creating the humidity issue. If you dry out the house the plants will need more water. If you water the plants they'll give off humidity. Conundrum.
Try getting rid of the plants and see how the house does.
Nick
To some people 6 plants is a lot to others 300 is nothing. Before we decide the plants are the problem lets see if the OP will give us a number.
I suspect there is an elephant in the house we just have not gotten the OP to tell us what it is yet.
Walta
Of course Walta.