How often do you run your HRV?

[Longknife]

When I first moved into this place, being a miser, I tried to never run the HRV, thinking I was just throwing heat outside needlessly.

Once I started getting EXCESSIVE moisture on the windows, and being more aware of indoor air quality, I started to run it more and eventually replaced it with a newer model. I've sinced replaced the windows with triple panes and condensation is far less of an issue. I have a split entry ranch style home, about 1800sq ft of finished space per level. Although almost 30 years old, I believe the house is fairly well sealed as the downdraft fan on the in counter range (located in the upstairs kitchen) will pull smoke out of my basement located wood stove if I'm not careful about it (i.e., house closed up, exhaust fan on high and I open up the door of the wood stove during a slow or smoldering burn).

Once I'm at a point where it isn't bringing excessive moisture into the house (late summer/early fall), I'll starting running it on continuous low speed, or "auto" which is 20mins of air exchange per hour. Anything about -5 degrees and below, I switch it to "eco" mode, which is only 10mins of air exchange per hour.... pretty minimal By this point in the winter, I'm definitely not worried about removing excessive moisture (unless I was having a party) but mostly concerned with just trying to maintain decent air quality. I've read some of the doom and gloom from the anti-wood burners about indoor air quality, and although I do take it with a grain of salt, I do believe air exchange is a good part of indoor wood burning.

Unfortunately I don't have make up air in the system or a fresh air intake hooked up to my SeeFire pedestal stove. I also never had the HRV balanced after replacing the old one myself, but will try a basic test once it warms up a little to see if I'm getting any significant over or negative pressure.

I'd welcome any thoughts on running an HRV in conjunction with a interior wood-burning appliance.

 

[jetsam]

I had to Google "HRV". Is that something they're putting in residential houses now? Looks interesting.

 

[coutufr]

I have a venmar model and use it mostly in automn when the dew point is below 10c outside and indoor’s RH is above 50 - 52%. In the winter I use it very rarely. The temperature being low outside, it provides some fresh air through all the holes (electric outlets ect). Also the stove pulls more air outside the colder it gets. The house sets itself at a RH around 40% in the winter and the temperature in the stove room is most of the time above 25C. Most of the windows are 5-10 years old with many being triple glazed so condensation is not an issue. What is the temperature outside your house in the winter time. If it is around freezing I would use the HRV like you do but not all the time unless you have a high level of humidity in the air outside during the day when it is warmer.

 

[Longknife]

I have a venmar model and use it mostly in automn when the dew point is below 10c outside and indoor’s RH is above 50 - 52%. In the winter I use it very rarely. The temperature being low outside, it provides some fresh air through all the holes (electric outlets ect). Also the stove pulls more air outside the colder it gets. The house sets itself at a RH around 40% in the winter and the temperature in the stove room is most of the time above 25C. Most of the windows are 5-10 years old with many being triple glazed so condensation is not an issue. What is the temperature outside your house in the winter time. If it is around freezing I would use the HRV like you do but not all the time unless you have a high level of humidity in the air outside during the day when it is warmer.

I'm near Ottawa... so not much different than you.

My indoor RH is less than 40% most of the time (35% right now). I realize bringing in the dry outside air doesn't help that, but it's an easy fix to put a cast iron kettle on the stove. I've done it in the past and it doesn't seem to cause any localized humidity issues or rapid steam production. Running it during the cold dry temperatures is not ideal (as I say, about 10 minutes of air exchange per hour, not a lot), however I like to think it's helping with indoor air quality. I don't believe my home is drawing enough "fresh" air through passive means given it's seemingly relative air tightness. Obviously the air the stove is consuming comes from somewhere, but everything I've read and experienced has led me to believe that it is not enough and that running like I do up to about -20-25C is a good thing.

I would have liked to have replaced my HRV with an ERV, however direct to consumer sales aren't that common and the HRV I installed (the largest Venmar that they carry at Lowes/Rona) was a direct swap (almost). Moisture considerations would be mostly out of the equation then, but I couldn't justify the added expense to myself at the time.

 

[Longknife]

I had to Google "HRV". Is that something they're putting in residential houses now? Looks interesting.

I'm pretty sure they are code around here, but I could be wrong. They've been very common for years at the very least.

Given how airtight homes are built now, they are a must in my books.

 

[coutufr]

ERV was what I thought I wanted before I got the HRV but most of the time I need to remove humidity from the house and the ERV can not do that. A ERV with a whole house dehumidifier when you are not cooling with the airpump would be ideal but overkill as per the Hvac guys I talked to. I understand that it would provide the opportunity to vent during winter and summer without bothering with outdoor humidity level. If you can run it and you can feel the difference in the quality of the air inside I think it is a good thing you use it. I think you are right to think that wood stoves are bad for indoor air quality and you make me realize that when the temperature is between 0 and -10 c , I should use it and humidify to compensate. My HRV is hooked to the main furnace and it can significantly bring cold air in the basement and in the bedrooms. Running the electric furnace at the same time would prevent that but with the wood stove I can not preheat the HRV incoming air.

 

[Longknife]

ERV was what I thought I wanted before I got the HRV but most of the time I need to remove humidity from the house and the ERV can not do that. A ERV with a whole house dehumidifier when you are not cooling with the airpump would be ideal but overkill as per the Hvac guys I talked to. I understand that it would provide the opportunity to vent during winter and summer without bothering with outdoor humidity level. If you can run it and you can feel the difference in the quality of the air inside I think it is a good thing you use it. I think you are right to think that wood stoves are bad for indoor air quality and you make me realize that when the temperature is between 0 and -10 c , I should use it and humidify to compensate. My HRV is hooked to the main furnace and it can significantly bring cold air in the basement and in the bedrooms. Running the electric furnace at the same time would prevent that but with the wood stove I can not preheat the HRV incoming air.

Yes, my biggest issue as far as indoor air quality is excessive humidity in the summer. This year we had an extremely wet summer, which not only meant a fair bit of humidity but also that the water table was fairly high, meaning my sump pump ran all year when normally it would be dry in June, which I *think* kept my basement slab cooled beyond usual. This led to me coming home a few times to slip on some water in my basement, only to notice the entire floor (mostly ceramic tile) was covered in water from condensation. My basement was extremely wet all summer before I realized I would have to start running my heat pump (air conditioner). I can keep my house quite cool without it (deep eaves, deciduous trees to the south block the midday sun, decent insulation, etc.) but I need to run it simply to control humidity in my basement. I have a 70pint humidifier that runs non-stop during the summer, but it is obviously not enough. I had considered another one for the other half of the basement, but I figured it was probably more sense to start running the air conditioner. I'm a miser, but I'll have to bite the bullet.

My HRV was a retrofit. It pulls from a single, centrally located vent near the ceiling in the second floor and dumps in the center of the basement/1rst floor. Not ideal, but the house is fairly open so I think it moves the air around alright. I just stoked the fire and walked under the HRV vent as it was running and noticed that the incoming air is fairly warm considering it's about -20C out. Since night is coming, and colder temps, I'll probably shut it down until morning. Part of the reason I also didn't like to run it as much was that I had a hard time keep the house up to temp with the stove alone. I really had to stay on top of it and block some rooms off to maintain a decent temp or try and make up ground for extended periods away from the house. With the new windows it doesn't seem to be a problem so I'm not as fussed about running the HRV a little.

 

[coutufr]

It is probably best to dry your house as much as you can in the winter while the air is dry. It was a very humid spring and summer. I haven’t used the heat pump much last summer either. You are not in an ideal situation with your basement but as long as you can manage it you are ok. The problem with over cooling the house to remove the humidity is that RH increases with the lowering of the temperature. It is a catch 22 in the summer. Maybe a whole house dehumidifier won’t be overkill in your situation. Humidity is very bad for a house if not kept under control

 

[Longknife]

I was definitely anxiously awaiting the fall/winter drier weather and the chance to get my stove going to drive the moisture out of the house with a vengeance. It got a little out of control and I didn't pay it the attention I should have during this busy summer. This year was really an anomaly weather-wise, so I'm hoping I never have to experience that extreme again. I'm down to about 34% right now and put the kettle on the stove lest I starting cracking stair treads or hardwood.

The water table is the worst part about this house, and it may be what drives me to build new on another piece of land. I always wanted a house that was passive as possible, but this one requires some management and use of energy. We really love this location though.

I will look into the who house dehumidifiers, although I think I can mange with a little more use of the AC and a little less extreme humidity around the house.

 

[Knots]

In the winter I run it between 11 AM and 3 PM. In the summer I run it from 9 PM to 4 AM.

 

[coutufr]

We are supposed to have more rain in the next couple of decades because of the weird stuff going on weather wise. Also you could theoretically heat with your stove to run the heat pump more in the june - july months. It sounds stupid I know but this is what a dehumidifier does, it would be really cheap for you to do (some wood and a marginal amount (a couple of $) of electricity a day). Instead of only being able to run the heat pump 2-3 h in a day in a 22C outside temperature you could run it a good 10 hours maybe. Doing that early in the summer could make things work for you with minimal investment. I would also consider putting a wood stove in the basement and heat from it in the spring to keep the basement warm and toasty. Water needs tons of energy to become vapor especially when the air is humid to start with