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Quattro 10-07-2009 01:03 PM

ERV / HRV / AAHX - Can I install it myself?
My house stays relatively humid in the winter. Especially the basement. I've made great strides in sealing up the cracks, installing weather-tight windows and doors, and made sure vapor barriers and insulation is up to snuff in the attic.

I have a 1-level house with a (mostly) finished basement. However, at this point the basement is not heated. It does have a cold air return, though. I presume this is where some of my excess winter moisture comes from. But, I want to keep it in the air loop (it is more or less "open" to the first floor via an open-ceiling staircase.

I'd like to install a heat recovery ventilator...also known as an HRV (or air-to-air heat exchanger). I have total access to the current forced-air duct system, and the utility area in the basement is unfinished. I'm pretty confident I can install this, but I'd like some pointers from others.

The biggest hurdle I can envision at this point is the fresh-air intake and stale-air exhaust. These need to be 4 or 6 inch holes in the band joist and siding, with I assume some sort of damped wall cap. Any insight here? Also, I have steel siding, so it could be a real bear to make a nice cut in. Ideas?

Thanks much, I appreciate the help! I'm hoping this measure will keep the moisture level in my house down to where it no longer condenses on the brand new windows I installed!

And FYI - we have fully functioning bath vent fans and a high CFM kitchen hood. We always run the fans during cooking and showers (and for a while after the showers)...and we still have a problem. It's the downside of sealing up a house!

Thanks much

inspectorD 10-07-2009 02:32 PM

I would have an energy audit and blower door test done on your house. Since all the improvements you have done has sealed up the home, it sounds as though you may have trapped more than condensation. Instead of an hrv, you need to determine the scource of the moisture, and see if that is the issue.

Causes for moisture, no barrier under the concrete floor, water vapor through concrete foundation,or lack of a chimney cap.
It is absolutly worth the $ to find other issues, and it gives you a new starting point to decide which course of action comes next.

Quattro 10-07-2009 07:51 PM

Well, the best I can come up with, is the moisture is coming from under the concrete floor. Everything in the basement is dry, however. There isn't a water problem, it's just moist. Right now, it's 63.7 degrees F, and 70% relative humidity down there. During the summer months, I occasionally run the dehumidifier, and I can get it to 70 degrees with 50% RH...but not much below that. I know RH will increase as temp drops (as a function of how much water the cool air can hold), so I'm not too worried about the 70% right now.

So, if there's moisture coming up from the concrete floor...there isn't anything I can do about that anyway, right? So, why not install an HRV?

I'd love to have an energy audit done, but I don't see how that would change the fact that I need to get drier air into the house during the winter.

Oh, and we don't have a chimney, so the chimney cap is out. The only other sources of moisture are house plants (we have a few, but it's not a jungle by any means), and cooking with gas. As I said, we run the range hood (which is a very high quality unit with a high CFM fan) during use. It's a 1370 sq foot main floor, and it's just my wife and I and our 2 year old girl. So, to me, that leaves the basement as the main culprit of the source of moisture.

travelover 10-08-2009 04:39 AM

You might find insight here..

inspectorD 10-08-2009 05:19 AM

the energy audit will tell you what is happening with your house now.
My questions are, have you lived through a winter since you have changed everything in the home to this point? The winter tends to be drier, what will happen in the summer with the hrv open to the exterior? Will it cause a new drafting effect?
No one can answer these questions without knowing where your starting point is, now that you have all these new improvements. What you had before is only a small part since you changed the house system.
Do you also have a gas furnace? Is the heat exchanger in good shape? This can also cause condensation and kill you slowly.
If the floor is the issue, there are floor moisture barriers you can install to help. We have come a long way with products. Check out your local concrete supplier for a good product.

These are just my opinions, and I don't know it all, but I do like to get a starting point on every job and go through solutions before I spend money or effort on something that I may not need, or makes the conditions worse.
Hope this helps.

Quattro 10-08-2009 08:55 AM

Thanks for the ideas, inspectorD.

I have indeed lived in this house over winter since the new windows and better sealed basement (windows and band joist). It's been upper 30's and low 40's overnight here lately, and already we are seeing some condensation on the very lower parts of the window glass (bedrooms and one bathroom only). So, I know it's going to be a problem again this year once the temp drops.

HRVs are installed in new houses all the time, why would mine be special as far as interaction with A/C in the summer? The gas furnace is original (22 years old), and probably does need to be replaced or at least serviced. It's a high efficiency model, though, so I'm not sure how the heat exchanger could be "killing us slowly". Can you elaborate on that for me?

I'm not arguing with you on the value of an energy audit...I just don't see how installing an HRV can make my situation worse.

I appreciate your input, and I'm not trying to argue with you...just trying to learn!


travelover 10-08-2009 11:24 AM

I think the inspector is just trying to save you some money. If the vent doesn't cure your problem, then you still need to diagnose the root cause and fix it.

A good home inspector has seen it all and can probably make good recommendations just by looking over the house and taking past experience into account.

Quattro 10-08-2009 11:46 AM

I get that part of it. I just don't know what other "mystery" sources of moisture there can possibly be...and how they could be fixed?

If there was a LOT of moisture coming from the concrete floor (and lower walls), wouldn't it be pretty damp? It's not. The only other sources of moisture in the basement would be the gas furnace and gas water heater (non power-vent). Both are circa 1986. Those could certainly be creating quite a bit of moisture, but they are both vented properly, and plenty of water vapor is seen escaping from their exhausts (outside). So, beyond changing those things to new units, what can be done? I think it all comes back to getting fresh, dry air into the mix. That's what an HRV does. And buying and installing one myself would be a heckuva lot cheaper than a new water heater and furnace!

Anyway...perhaps I'll call a local energy expert and see what they say. Maybe I can get away without the audit if they have some free advice. I wouldn't be so worried about it if my truck didn't need transmission work! D'oh!

travelover 10-08-2009 12:36 PM

Did you read the web page that I linked to regarding concrete floor moisture?

There is a simple test there where you tape a 18" square plastic sheet on the concrete floor for, I think, 16 hours to observe moisture passing through the floor. That is a simple test that should answer your question. You can do a similar test on the walls.

Regarding the furnace and water heater - hopefully you have a CO detector or two in your home and these should warn you of a heat exchanger leak or backdrafting.

Good luck.

Quattro 10-08-2009 01:03 PM

Yup, I've read the article, and I've performed the plastic test (previously).

And yes, I have a CO detector, and it has always read zero.

Thanks for your help. I'll do the plastic test again to see what I get.

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