ERV / HRV / AAHX - Can I install it myself?

Discussion in 'HVAC' started by Quattro, Oct 7, 2009.

  1. Oct 7, 2009 #1

    Quattro

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    Massive Tool Belt

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    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
     
  2. Oct 7, 2009 #2

    inspectorD

    inspectorD

    inspectorD

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    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.
     
  3. Oct 8, 2009 #3

    Quattro

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    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.
     
    Last edited: Oct 8, 2009
  4. Oct 8, 2009 #4

    travelover

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  5. Oct 8, 2009 #5

    inspectorD

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    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.
     
  6. Oct 8, 2009 #6

    Quattro

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    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!

    Thanks!
     
  7. Oct 8, 2009 #7

    travelover

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    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.
     
  8. Oct 8, 2009 #8

    Quattro

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    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!
     
  9. Oct 8, 2009 #9

    travelover

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    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.
     
    Last edited: Oct 8, 2009
  10. Oct 8, 2009 #10

    Quattro

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    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.
     
  11. Oct 8, 2009 #11

    inspectorD

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    I agree with your reasons, and the heat exchanger can cause water issues in a home when it has a leak in it. I'm wondering if your co detector is working.:confused:
    I am also trying figure out where the moisture is comming from, sometimes it is all things added up to create enough to cause the problem.
    From here it is hard to tell you where to start, but the hrv is one solution to the exchange of air for the furnace, not the solution to the issue of the moisture.
    The reason I say to get an expert in there is, you may be missing something you just do not recognize as an issue. Some folks seal up the house with insulation, new windows and weatherstripping...but do not seal the attic pull down staircase.:eek:
    Try another set of eyes on the house, or call some folks with questions. Your local heat folks will come out to take a look at your issue if they think they can make a change, ask there for some advice.
    To me this is a whole house solution that needs to be addressed, it may take more than just the hrv.
     
  12. Oct 9, 2009 #12

    Quattro

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    Here's an interesting thing I just discovered. I have one of those little digital temp/RH meters, so I placed it in the basement last night. Then this afternoon I moved it up to the main floor bedroom, on the opposite side of the house from the basement location.

    Here's what it read:

    Basement: 61.7 degrees / 70% RH
    Main floor bedroom: 68.4 degrees / 64-65% RH

    This tells me that both air systems are basically the same! The basement probably only seems more damp because it's cooler.
     
  13. Oct 9, 2009 #13

    inspectorD

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    This is why I suspect your furnace heat exchanger, I hope I am wrong and it is a accumulation of a couple of issues, but i would have it inspected by the heating Co.
     
  14. Oct 9, 2009 #14

    Quattro

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    FYI - The second plastic test (in two locations) came up dry. So, I doubt the excess moisture is coming from the floor.

    If the heat exchanger was bad, wouldn't our CO detector pick it up? It's only a couple months old. The previous one we had never went off either.
     
  15. Oct 10, 2009 #15

    inspectorD

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    Could have 2 bad detectors, stranger things have happened.
    Does your dryer vent to the outside?
    If you can get into your furnace, a quich way to see if there may be leakage is to hold a mirror up to the exchanger area, if it fogs up, you have a leak.

    Look at all the flue connections also, I have seen them broken at the unit or not even connected.
     
  16. Oct 10, 2009 #16

    Quattro

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    If we were getting a lot of CO from the heat exchanger, I think we'd be pretty sick. The furnace has been on for over a week now (since overnight temps have been in the 30s).

    The drier vents outside, and that is using rigid 4" duct. The vent cap outside is accessible, and when the drier is on, there is a solid stream of moist air coming out.

    I will try the mirror trick on above the heat exchanger. There is an adjustable vent just above the evaporator I can remove and put in the mirror.

    BTW- is there supposed to be condensate coming from the drip tube during heating? I'm not sure, but I think I saw a little this morning near the floor drain (which is where the drip tube ends up).

    There is no flue, per se. it's high efficiency, so there's just the one 3" PVC exhaust (might be 2.5"). I can check the connection at the furnace.

    Thanks for stickin' with me, D!
     

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