Is a HRV the way to go?-installed/update

[mike31154]

Originally Posted by sphelps

My house is new and it has a simple exhaust fan plumbed in from the cold air return to outside. Does the same thing as an HRV but without the heat exchange. I thought about upgrading but I figured I'd leave it for at least a year before I bothered. I have it connected to a central thermostat that controls humidity levels as well with the exhaust fan and the humidifier. I believe most of the time HRVs are controlled either by simple timers, local humidistats or even just a light switch. Anyways I watched the heat bills last winter when I first connected up the exhaust fan and control and I didn't notice any difference in consumption. I have 100 gallons open top upstairs and about the same worth of open sumps downstairs but there is a lot more exposed water surface than a typical 200 gallon system. The thermostat I use also has some other features it uses to limit window frost, not sure exactly but it works and it's a different setting than the set humidity which is still maintained.

So I guess for me I wouldn't bother with the HRV, I doubt the extra cost and install would ever pay off. But it will likely depend on the demand for it but there are other options for humidity control. You should also check your furnace, it should draw in some fresh air when it operates and many times moisture and mold problems are a result from poor air circulation, not always directly a result from high humidity from lack of ventilation exchange.

After reading through some of the info provided in the links from Delphinus, I'm not convinced an HRV is necessarily useful or cost effective for everyone. There are a lot of factors to consider before forking out the dough for one of these, even if the government is providing some incentives. It really seems to be very dependent on age of home, how well it's sealed & more importantly the climatic conditions where you live in the winter. Seems to me having a code requiring HRV in a place like Vancouver makes no sense. It never gets cold enough long enough for the heat exchange portion of the system to provide any payback, nor is an HRV effective for humidity control in the summer. Well designed exhaust system similar to what sphelps has should work quite well to keep humidity under control.

Not sure I follow how exactly your system works though. The exhaust fan pulls air directly from your furnace cold air return? Is there another fan or at least opening to the outside to allow fresh air in to replace the exhausted air? My house was built in the late '50s and there are plenty of places for fresh air to get in. I have a fireplace in the basement as well as one in the living room, so I need to figure out if exhausting air without providing incoming would cause backdraft thru my chimneys. I also remember when I replaced the furnace in the condo I lived in in Ottawa, new code required the installer to run a simple duct from outside to the furnace to provide fresh air.

EDIT: Just found another link worth checking out. Good discussion on HRV, ERV and some of the pitfalls that may be encountered when considering any kind of ventilation system.

http://www.greenbuildingadvisor.com/...ngs/hrv-or-erv

[rayjay]

For me, I went with the HRV rather than the ERV because the Lifebreath engineer I dealt with (factory here in London) said the ERV can freeze up in winter and they never advise ERV when temperatures routinely hit below -5° C in winter. If you don't have that situation, an ERV could be considered, again, depending on just what you are looking to accomplish.
He also did calculations using winter house temperatures and square foot of all open water surfaces and temperature of the water in the tanks to figure out what size HRV would be needed for the volume of my home.
Lastly, he advised me NOT to use the humidistat as when the HRV is not actively running, the air exchange is not occurring and air exchange was important to me to keep pH from dropping too much in the tanks.
In our location, surrounded by the Great Lakes, humidity is extremely high in summer and I certainly don't want an ERV that is going to reintroduce some of that moisture back into the incoming air.

[sphelps]

Originally Posted by mike31154

Not sure I follow how exactly your system works though. The exhaust fan pulls air directly from your furnace cold air return? Is there another fan or at least opening to the outside to allow fresh air in to replace the exhausted air? My house was built in the late '50s and there are plenty of places for fresh air to get in. I have a fireplace in the basement as well as one in the living room, so I need to figure out if exhausting air without providing incoming would cause backdraft thru my chimneys. I also remember when I replaced the furnace in the condo I lived in in Ottawa, new code required the installer to run a simple duct from outside to the furnace to provide fresh air.

The exhaust fan only works when the furnace is on, just like the humidifier. So if the exhaust fan is active it creates a negative pressure and the furnace will draw in make up air from outside. And yes the exhaust fan draws air directly from the cold air return.

[MarkoD]

In my house we have a switch by the thermostat that turns on all 4 bathroom exhaust fans and turns on the furnace. Moisture gone in no time.

[sphelps]

Another thing to check is your humidifier, make sure it's not the source for the moisture problem. Ask yourself how it's controlled and if it makes sense. Often they use a local humidistat that isn't accurate to begin with and it's location isn't effective. Disconnected the humidifier for a while and running the furnace fan more often and observing the change in humidity should tell you if there's an issue.

[mark]

Originally Posted by MarkoD

In my house we have a switch by the thermostat that turns on all 4 bathroom exhaust fans and turns on the furnace. Moisture gone in no time.

and all that warm air you spent the bucks heating, which is the purpose of the HRV to recover. Big question is how much that heated air is worth vs cost of unit? Won't bring in the air quality factor.

[wolf_bluejay]

I've had mine for about 2 years now. Just before I installed it I was going through all the eco energy rebates in BC for the new furnace and heat pump, insulation etc. I found that with all the extra air sealing I went from having fogged up windows to where I was having water running down the walls on cold days.
It was nasty, with all sorts of mold issues. So, with the fact that I got a bunch of rebates for the HRV I installed my own. I spent a little under $600 for the unit and installed it myself. I got back about $500 on rebates. So the thing cost me very little.

The problem of wet windows went away. But even more so, me and the family felt less tired in the house, it got less muggy we we had a lot of people over (I kick it onto high then), and smells don't linger in the house, and much less dust. I like it so much that I would put one in a house even if I didn't have the fish tank.

That said, as I couldn't do it with the way my house is, but for my parents place they swapped out the bathroom fans with an HRV. It kicks into high for 30 minutes when you hit the fan button in either bathroom. It dumps the return air into the main living room.

For them, they didn't need to replace 2 bathroom fans at about $200 each for large quite ones so the unit was only a few hundred more. Considering they are on electric heat (and no air exchange in the house) the pay back was there and the comfort level was much better.

I can't see how you could lose with one unless you spent a lot to get one installed.

[Veng68]

Just wondering what is involved in the installation of an HRV unit in a finished basement and a mech room that is in the center of the house? Will I have to take down a lot of dry wall to do an installation?

Cheers,
Vic

[sphelps]

Depends on the unit but you can use your furnace to distribute the air rather than a fully independent HRV. Then you would simply drill one extra hole in the mechanical room wall for exhaust and run the HRV exhaust line from there to the furnace cold air return. The HRV intake would go inline with the current furnace fresh air intake. This way no drywall has to come down, no major modifications.



Or even like this:


Of course you need a forced air furnace and it's fan will have to operate when the HRV is on.

[jimbo222]

Wow lots of great info and opinions on HRV/s Here's mine...

We have to keep in mind that a HRV is an AIR EXCHANGER and not only a De-humidifier.
The De-humidification is an added bonus this unit features, or provides.
It is quit amazing how much OXYGEN is reduced in the home and not replaced. You probably dont notice it but you are probably getting tired and sleepy. Your Furnace uses oxygen as it burns, your water tank uses oxygen when it's running, each person in the house is using oxygen, and MOST IMPORTNTLY our aquarium's are using it all up. I guaranty you will have more stable PH if you install a Air Exchanger, usually will go up by .2 or .3.
I realize some homes have fresh air and combustion air intakes to the furnace room but this does not provide air exchange, but prevents a negative pressure in the house.
Personal y I think An HRV is a Very important unit in the climate that we live in. < if installed properly> Not only as De-humidification help but for Healthy Fresh outdoor air.

AS mentioned above aswell make sure that your humidifier on the furnace is installed correctly, especially if it;s a new home. < iv been to too many home's where the humidifier was installed incorrectly and runs anytime the furnace comes on >

The money we put into this hobby... , $700 unit is nothing in the long run, and will save your home from mold.