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Old 12-21-11, 12:38 PM   #1
strider3700
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Default Fill me in on HRV's, what to look for, how to hook up

My house has been getting tighter and is now starting to get to the point of feeling stale in the middle of winter with the windows closed for weeks on end. So I'm thinking of getting/building an HRV. I was following the build it yourself thread since most were $800-$1000 but recently ran across a commercial unit available here for only $380 and I see one online here for $500.
Home Hardware - AIR EXCHANGER, SYMPHONY 1
Home Hardware - AIR EXCHANGER, HV1.5

What I have no idea is what values mean something useful when it comes to efficiency. Also how do I install these things? My house has central air with ducts running to every room. Can I pull air out via the return lines and return fresh into the feed trunk or do I have to add vents to every room I want air going into/out of?

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Old 12-21-11, 01:10 PM   #2
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You can install connections into the duct work, no need to new runs, but I would suggest you put an exhaust in your bathroom and use instead of the exhaust fan you might have been using.
I installed a constructo 1.0 by venmar this year. Their installation manual is informative.
Installation Manual
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Old 12-21-11, 01:28 PM   #3
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thanks, I don't currently have a bathroom fan but need to add one which got me started down this road...

so looking at that diagram it looks like adding a couple of intake runs upstairs in the bathroom and a couple of other key locations would be optimal and then return the fresh air to the supply line for the heating.
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Old 12-21-11, 01:37 PM   #4
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Quote:
Originally Posted by strider3700 View Post
...I have no idea is what values mean something useful when it comes to efficiency...
This is because the web site is giving you no information that pertains to efficiency. You would need to go to the websites of the manufacturers and find the model you want and look at their information on efficiency.

If you have gone to the trouble of making your house tight enough that it feels stuffy, you have done a good job of reducing air infiltration... not always so easy to do. So you should seek out (or make) a high efficiency HRV.

If you can't find efficiency information, you probably shouldn't buy the unit. Efficiency information is something that manufacturers are proud of, if their HRV is a high efficiency unit.

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Old 12-21-11, 01:55 PM   #5
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One thing to keep in mind is that older ventilation systems assumed that there was enough air leakage in a house to naturally supply fresh air.

And the older ventilation systems supplied NO fresh air and exhausted to the outside NO stale air.

Whenever a non-vented furnace or gas water heater fired up, because inside air was used for combusion air, it created a negative pressure inside the house, which pulls in cold, fresh air.

HRVs are built with a fan to exhaust stale air and an equal-sized fan to bring in fresh air, thus maintaining zero pressurization.

However you hook up your HRV, you will want to maintain the zero pressurization.

You will also want to assure that you have no appliances that use inside air and can create negative pressurization.

This could mean adding an outside air inlet to furnace room, or water-heater closet, or even stove hood power vents.

It could be a lot of hassle, but it will mean that you will have no net positive pressure, which would push out heated air, or net negative pressure which would pull in cold unheated air.
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Old 12-22-11, 06:37 AM   #6
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Don't overlook your laundry room when you are making your design decisions, the washer produces considerable amounts of moist air, and your dryer moves A LOT of air! Building code requirements for new home construction require that your laundry room, as well as the kitchen and all baths, be connected to your HRV.
Another consideration is the humidity levels in the house. It may not be an issue on Vancouver Island, but if you are bringing in outside air that is very cold and very dry, you may find the house gets too dry very quickly. An appropriate humidifier, freestanding or furnace mounted can correct these dryness problems quickly. A beneficial side effect is that the correct humidity feels warmer than dry air.
My last piece of advice is to keep your ongoing maintenance procedures in mind during your install. You are going to want to keep your ducts straight, and levelled so that they drain properly, and you are going to want to disassemble, clean and inspect all the components as required. Remember, you are moving warm, moist air, laden with organics ( dust, dander, pollen, and ?), and the potential exists for mold growth.

Almost everyone I've spoke to who has had an Hrv retrofitted to their home has noticed air quality improvements almost immediately, it will be money and effort well spent.
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Old 12-24-11, 08:04 AM   #7
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Really tight houses have dryers, range hoods and bath fans also and the way the designers deal with the depressurization issue is to assume that in moments of depressurization more air will be drawn through the HRV. As far as I know there have been no studies on this.
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Old 12-27-11, 01:13 PM   #8
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Quote:
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Really tight houses have dryers, range hoods and bath fans also and the way the designers deal with the depressurization issue is to assume that in moments of depressurization more air will be drawn through the HRV. As far as I know there have been no studies on this.
I think that the developments in this area are moving really fast right now.

I suspect that ten years down the road, looking back to how we think about these issues today, our current thinking will seem pretty primitive...

* * *

The dryer part seems pretty straight forward. I think it should be put in it's own closet, with outside air coming in.

The range hood problem really has me going right now...

The best (and I don't think it is very good) solution I've heard from a local Passive House builder is to use a recirculating range hood that 'condenses' grease vapor in a screen, and use the HRV input in the kitchen to extract the higher humidity kitchen air. Boost switch in the kitchen & bathroom.

I'm not a big fried food guy, but I really doubt that the screen thingie will do a very good job of capturing grease and oil vapor. So then the vapor gets deposited in the HRV and walls and cieling.

I have a friend who has put a 'modern' extractor hood over his cook top. The hood think looks like a hovering glass flying saucer with a stainless stack attached. It relies on HUGE volume of air to capture cooking smoke that really wants to go up past the flying saucer. His house is very small (< 600 sq. ft.) and extremely tight, so his hood will not develope HUGE volume without replacement air. His options are:
  • Open a window (a total cop out)
  • Plumb in a power replacement air fan system under the cooking counter (lots of work to do that)
Personally, I think he has become a slave to style and would be better off with an extractor hood that works with physics rather than against physics, and therefore did not rely on HUGE volume to work.

But there's still the HRV part...

He has a tiny Panasonic ERV that runs about 30 CFM and will be totally overwhelmed by his extractor hood.

I'm still looking for a better solution.

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Old 12-27-11, 02:38 PM   #9
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At the moment we have a recirculating range hood in the kitchen. It works but not great.

The house never had any vents for kitchen or bath added when built 50 years ago. When I redid the roof I specifically added venting for the bathroom and kitchen but hooking them up hasn't happened yet.

As things already are I need to add an air intake to bring in replacement air going out via the woodstove. The stove being in the middle of the house means I can't directly plumb it outside and will probably just dump the cold air into a small "closet" right beside the chimney. This area gets warmed by the stove via the chimney so that will help deal with preheating in that case.

The range hood isn't likely to be running enough to make me too concerned about cold air coming in when the woodstove isn't running.

So the biggest concern is the dryer drawing air in when the woodstove isn't running and it's winter. That could be corrected with a closet and outside venting I suppose. I'll have to decide if it's a serious enough issue to target.

It's too bad they don't have heat exchangers that can reliably deal with "dirty" air. I'd love to plumb the dryer and kitchen range into one and just be done with it.
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Old 12-28-11, 09:06 AM   #10
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Wow...lots of info to process. So is sealing up your house really the best thing to do then? Especially with home builders really not yet having figured things out as far as pressure, moisture and air exchange? I bought a 1987 house this fall and I was thinking of sealing it up and sticking in an HRV with the new furnace/AC that we're going to need to buy. But now I'm wondering if I even want to do that, because then it will be to dry in the house and we have hardwood floors. And I really don't want to put in a whole house humidifier because I've read that they use tons of water and we use well water which would mean the filter would need cleaning ALOT. I'd almost rather leave things unsealed and just let the air get sucked in that way. I don't know, it's very confusing when you don't know exactly what's going on.

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