Hello... I was just doing some research on problems with ice buildup on my windows in the middle of winter when it's very cold... we live in Montreal and the temperature can easily dip to -20c or lower.

We moved into our home approx 2 1/2 years ago, the house is approx. 6 years old and has an Electric Carrier furnace, Carrier A/C unit with a vanEE Furnace Air Exchanger with Heat Recovery(vFAE115M) it's separate from the furnace but attached to the same vents. We also have a humidifer but it has been turned off because it would never stop (something defective) but we have too much humidity anyway.

I've been trying to figure out the air exchanger and figured out that it's attached to a honeywell relative humidity control (I presume that it's a humidistat?).

The humidity level in the house Saturday morning was at 65%, I switched the humidistat down to 40% and noticed that it automatically opened the louvers in the Air Exchanger and has kept them on ever since. The humidity has reduced slightly to 62%.

I raised the heating from 22c to 23c (not much of an increase but we don't want it uncomfortably warm even in the middle of winter).

I have also turned on a standalone dehumidifier unit which has been running all day. This has also improved the situation. The humidity level is now at 60%. I currently do not have any problems, the temp outside has been relatively mild for Montreal (above freezing) so I haven't had any condensation on the windows for the past few days but I'm starting to monitor the situation and getting as much advice as I possibly can to ensure that we don't run into the same problems as the past 2 winters. Also, a couple of weeks ago the temperature was colder and the condensation had already started but I wasn't watching the humidity levels, etc...

What else can I do to improve the situation? We have tried to keep the bathrooms fans running for approx. 10mins after showers and use the stove top hood fan on while cooking.

Is it possible that there is a problem with the windows? Air leakage... would this be a problem and cause excessive ice buildup?

Would it be possible to upgrade the fan motor on the furnace so as to improve the air circulation in the house? As it happens the 2 bed-rooms with the most ice buildup happen to have the least airflow through the floor registers/vents and they windows happen to be north facing therefore the least amount of exposure to the sun!

What temperature level should we keep the house at? I realize that by increasing the heat it will improve the situation but how high must you heat to improve this situation. We normally prefer a indoor temperature of 22c - 23c.

Any help you can provide would be greatly appreciated... let me know if you need additional information.

Regards.
Renato.

Before you do anything with your HVAC system you need to find the water source that is causing the high humidity.

I have a smoke machine and also a electronic draft gauge that I use for testing for air leakage. It is the only way to really find out where the air leaks are. Also a blower door test will give you an idea about how tight your home is.

Thanks for your reply.

I've been thinking about this for some time and I've been trying to get a users manual for the Air Exchanger since I knew next to nothing about working/adjusting the air exchanger. I knew the concept which is great! I have since received the users manual and can see how the humidistat works the air exchanger.

I'm wonder whether the air exchanger was even opening up and bringing in fresh air the last 2 winters? If this was the case then I presume that this would explain the problem... correct? The humid air is not being vented out of the house except through the stove hood and bathroom fan which is not sufficient.

What I don't understand is how the system works with the Air Exchanger... if the outside air is very humid because it's raining or snowing and I'm bringing in this fresh/outside air how is it helping the situation? As far as I have seen there is nothing in these Air Exchangers which stop the unit from introducing the outside air based on the humidity level of the outside air? The unit is only controlled based on the relative humidty setting you set on the humidistat correct?

I currently have the Humidistat set such that the air exchanger is open all the time (I'll planning to play with it such that it doesn't stay on all of the time and see what happens to the relative humidity in the house). So if I leave it as is during the winter I'm introducing cold air all of the time and even with the Air Exchanger with Heat Recovery I'm still losing tons of energy (hot air).

Any other thoughts or comments about this..?
You mentioned: "I have a smoke maching and also a electronic draft guage that I use for testing for air leakage." I don't have either and don't think I know enough without much help what to do with these so I'm trying to regulate things with what I have available.

I presume that I should be able to regulate the problem with the air exchanger and temperature setting in the house? Other than wait & see and some trial & error do you have any other thoughts on how I could adjust the problem? The air exchanger is currently not creating any moisture or condensation (i.e. no water being sucked out that I see dripping from the hose at the bottom of the unit).

P.S. The Relative Humidity is currently at 58%. Is this very high?

Thanks again.
Renato.

Renato,

I moved into a new house just outside of Montreal. The first winter I had the same problem. My humidity was over 50. I didn't know much about how the exchanger worked. I read a lot about it during the last few months in order to prepare for this winter. Apparently, sources say that the indoor humidity should hover around 35-50 degrees, depending on the outdoor temperature. A little bit of condensation on the lower borders of the windows is normal. But if you have ice, there's a problem, and you probably have condensation in unseen areas of your home as well, such as the attic. In winter, if you reduce the humidistat to a setting lower than the relative humidity of the home inside, the vents inside the air exchanger will open, allowing outside are to enter your home through your furnace. In winter, the outside air contains low humidity, and in turn this will lower the humidity of your home. I use my humidistat in conjunction with my humidifier to maintain a 40% humidity reading inside my home. I found that if I keep my humidifier too low, no matter what I set my humidistat to, it will always be too low. I play with both to keep an even balance. Hope this helps.

KC