HRV or Whole house dehumidifier..which one?
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  1. #1
    Join Date
    Feb 2009
    Location
    West Mi
    Posts
    2

    HRV or Whole house dehumidifier..which one?

    Hello all, I'm new to this forum jazz so here I go.
    This message is going to seem long-winded, but I want to provide as much info as possible for a accurate analiysis, pardon me on the spelling errors.
    I have a 8 year old stick built ranch home in West Michigan,1200 sq.ft. 8ft. ceiling upstairs, 1200 sq.ft. 9ft. ceiling downstairs in the basement. 2*6 exterer walls with blown in fiberglass insulation and caulked from head to toe,(I know, a tight house). I have duct work for my LP furnace and Air Con. and I also have a 8 inch fresh air inlet tied into my cold air return duct work, (thats code in my area).
    My basement was finished, (not the ceiling) untill I suspected I had a mold problem, so I ended up ripping all of my 2*4 insulated basement walls out and guess what I found...you got it..Mold. My poured concrete walls were soaked in certain areas and I traced the water to my sweating baseboard joice ends dripping down to the concrete wall below creating a mold breeding ground. And yes my joice ends were insulated. My contractor and I inspected every inch of the house to see if water came from the roof or attic, outside siding leakage, leaky plumbing or what ever. Nothing.Yep, high levels of humidity was the cause. I cleaned up the mess and bought a dehumidifier and the moisture has stopped for now.
    I just want to also mention that my upstairs windows have condensation on them quite a bit, I have strange allergies that I never had before and my 2 kids seem to get sick with colds and fevers allot.
    So with all this information I have disclosed for you with my geographical area taking in consideration, Which route should I go,,, HRV or a whole house dehumidifier? From what I have read on the internet it seems that the HRV is my best choice but nobody (HVAC Installers) in my area has a clue about HRV's or has much experience with them. I just spoke with a HVAC Pro on the phone and he stated that a whole house dehumidifier is the way to go, but I'm not sure if he is right. Sure it will dehumidifi, but is it fresh air or the lack there of the real issue?
    Any and all info would be great, such as what to get,make and model you prefer and if it has worked for you in such a case like mine.

    Thanks for your time.

  2. #2
    Join Date
    Jan 2009
    Location
    Northwoods, Wisconsin
    Posts
    77
    My first recommendation would be to have your indoor air tested. It sounds like you still have a large source of contamination. Several things will cause the symptoms you are describing. Volatile organic compounds(VOC's), Allergens, Carbon Monoxide, or a combination of these things. Mold is very hard to get rid of, and if you had it in one place your likely to have it in another. Indoor air contamination continues to rise with time and Oxygen levels continue to fall, A fresh air exchange is crucial to good long term health. Dehumidification should be done by a dehumidifier and fresh air exchange should be done by an Air to Air Exchanger (HRV, ERV, Etc.). The fresh air inlet that you mentioned connecting to your duct is only to prevent your home from being drawn into a vacuum when you use an exhaust fan (kitchen, or bath), and cannot be counted as a fresh air supply.
    So #1 Test indoor air and identify problem.
    #2 Perform air exchange in home daily, you can open all doors and windows for 5 to 10 minutes a day and even use a fan until you can afford an Air Exchanger.
    #3 Work to neutralize the source.

    Best of Luck

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    Certainly your moisture level in your home is high and you need some additional fresh air to purge indoor pollutants/moisture and renew oxygen. Your home does breathe some and how much supplemental fresh air ventilation does your home need. If your home was perfectly air tight and you needed 150 cfm of fresh air 24/7 during the winter, a HRV is a good choice with a 5 year payback. If you home needs an additional 60 cfm of fresh dry air for 12 hours per day to keep windows from sweating, a make-up air ventilation system is most practical.

    Regarding a ventilating dehu as a solution to the winter moisture problem you are having- a ventilating dehumidifier will provide the 60-75 cfm of fresh air throughout the year. The dehumidifier does not dry the home during cold weather. The fresh dry, cold outside air keeps the home dry during winter. The dehumidifier is there for the rest of the year. You need 75 cfm of fresh air whenever the home is occupied regardless of the moisture content of the air. During the winter, the 75 cfm keeps the home dry. During the spring/summer/fall, you need the dehumidifier to remove the moisture in the fresh air and and from the occupants. Green grass climates need 30-60 pints/day of dehumidification to maintain <50%RH throughout the home.
    How did you fix the moisture condensation problem at your rim joist? Most use fiberglass insulation to stuff the ends of the joist/rim joist cavity. This allows moisture to infiltrate the fiberglass insulation and condensate on the cold rim joist surface. The condensate inturn drips down the mud plate and down the wall. Use snug fitted aluminum faced 2" foam blocks to insulate the joist cavity with the aluminum on the inside for a vapor barrier. This moisture condensation problem is common even in dry homes use fiberglass to insulate the joist rim joist cavity.
    Get enough fresh air into your home to stop the condensation problem asap. Cracking windows and operating fans can do this immedeately. Provide the fresh air whenever the home is occupied year around. Maintain <50%RH throughout your home year around. A ventilating dehumidifier will do this. A HRV with good dehumidifier will do this also. In the past, I used HRV/ERVs to provide fresh air to homes. I found during cold weather most homes get almost enough fresh air and but not enough during the milder weather. I needed to cut back on fresh air during the winter. Also homes that get enough fresh air during the rest of the year are damp. Therefore I use a ventilating dehumidifier mostly now. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #4
    Join Date
    Feb 2009
    Location
    West Mi
    Posts
    2

    To Teddy Bear

    Yeah Teddy Bear I have'nt reinsulated the joist ends yet, not untill I get this issue resolved. I can keep a close eye on them now to make sure they stay dry.I also figure that the house will breath a little more now. Are you sure that the foam boards with a vapor barior is a good way to go? I would hate to install them and seal them in and not know what is happening behind them, but I will have to insulate sooner or later. So you think that my best bet should be a ventilating Dehud then? And do you have any Brands that you have had good luck with? I like Lennox products but I'll go with anything that is good quality, dependable and does not cost millions.

    Thanks for responding.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    The key to using foam blocks with foil face is to make the block fit tight enough to stop the moist house air from getting to the cold rim joist. Caulking the edges of the foam to close gaps works.
    I have been envolved with Santa Fe, Ultra-Aire, Honeywell dehus for many years. There are others. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  6. #6
    Join Date
    Apr 2002
    Posts
    11,808
    something is wrong if you are not getting enough fresh air with an 8 inch intake. If it is a flex duct maybe it is collapsed or you have some kind of blockage or a damper shut off. Check the duct, make sure the intake hood is not clogged up with dead insects and dirt.

    An 8 inch intake is going to pass way more air than an under powered ventilating dehumidifieir. Get some proper ventilation to solve your winter problem and avoid practises like hang drying laundry in the basement

    If you have a musty basement in the summer time, by all means use a dehumidifier, that is its real purpose in life
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  7. #7
    Join Date
    Nov 2007
    Location
    Rochester, MN
    Posts
    80
    Quote Originally Posted by teddy bear View Post
    ....
    Most use fiberglass insulation to stuff the ends of the joist/rim joist cavity. This allows moisture to infiltrate the fiberglass insulation and condensate on the cold rim joist surface. The condensate inturn drips down the mud plate and down the wall. Use snug fitted aluminum faced 2" foam blocks to insulate the joist cavity with the aluminum on the inside for a vapor barrier. This moisture condensation problem is common even in dry homes use fiberglass to insulate the joist rim joist cavity.
    .... Regards TB
    TB,

    I'm considering my options for sealing up my rim joists, and was weighing the difference between the foam board and the fiberglass batts. The fiberglass batts are a lot easier to install since cutting foam board isn't all that fun, especially when you have to use expanding foam or caulk to seal every one up (and I have a lot to do). One difference from the OP is that I don't get any condensation around my rim Joists. Do you still think the foam board is the way to go? Here is a picture of one of my rim joist spaces.


    Edit: After posting I realized that this might violate the no DIY on this site. My only hope is that I may be shown some leniency because this type of work wouldn't necessarily be done by an HVAC expert.
    -D in MN

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    If you want to keep moisture levels in the 30% RH for comfort and you have 0^F outside, a snug foil faced foam block with an air tight seal is the way to go. If you operate your home drier and you are willing to forgo insulation in the rim area and have warm basement, maybe no insulation will not have any condensation problems. Insulation that allows house moisture to come in contact with the cold rim and there is condensation. Good pictures, did you have mold behind the old fib gl insulation? Regarding carnaks comments, our ventilating dehus have the right amount of fan power to get the proper amount of fresh air the application. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #9
    Join Date
    Nov 2007
    Location
    Rochester, MN
    Posts
    80
    Quote Originally Posted by teddy bear View Post
    If you want to keep moisture levels in the 30% RH for comfort and you have 0^F outside, a snug foil faced foam block with an air tight seal is the way to go. If you operate your home drier and you are willing to forgo insulation in the rim area and have warm basement, maybe no insulation will not have any condensation problems. Insulation that allows house moisture to come in contact with the cold rim and there is condensation. Good pictures, did you have mold behind the old fib gl insulation? Regarding carnaks comments, our ventilating dehus have the right amount of fan power to get the proper amount of fresh air the application. Regards TB
    This winter the only time our RH dipped below 30% was when we had the -20 to -30 degree weather. I'm sure you remember it . I keep my IAQ set to 40% with frost control of 5 and my steamer keeps up nicely, running between 5 and 8 hours a day working to replenish what my HRV takes out. My house has never had any insulation in the rim joists. I've inspected all of them for air leaks and haven't seen any mold. With the fib gl insulation I would use a staple gun and staple the faced insulation to the studs which should give me a vapor barrier. I had pretty much decided to go this route but your comments have got me thinking about the foam board again. hmmmmm
    -D in MN

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    No insulation is better than using fiberglass with foil. Try one fiberglass joist cavity. Place a %RH behind the insulation next to the rim joist. After a very cold night remove the insulation quickly and read the meter. It will be near 100%. Forget any insulation that allows moisture from the house air to infiltrate behind the insulation to the cold joist. The seal must be air tight. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #11
    Join Date
    Feb 2009
    Location
    Chapel Hill, NC
    Posts
    1

    Our experience in North Carolina

    I'm in Piedmont NC (Chapel Hill for you sports fans), and the best practice protocol for rim joist insulation is indeed to use caulked foam blocks for all the reasons TB indicated. Sprayed closed cell foams are beginning to be used as well, both in sealed basements/crawlspaces and on the undersides of roof decking for sealed attics.
    Of course, you folks up North have much more to worry about from winter condensation issues than we do, so I'm finding this discussion to be most educational.
    We have to cope with approx. 8 months of dehumidification control due to high ambient outside moisture conditions, so coupling a Santa Fe or Honeywell DH-90 type device to our homes w/ a motorized ventilation duct to the outside for IAQ concerns is typical. We supply 15cfm per person or 75cfm minimum during building occupancy times as a design reccommendation.
    Winter RH levels do tend to take care of themselves usually and fall into the 25% to 35% range. I have had clients push things via humidifiers to as much as 45% and usually get away with it, but of course we try to talk them out of such practices.
    These milder winters we've had the last few years down here have fostered such behavior.

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    Just to let you know. You now have a friend. There are not many progressive a/c types in this forum. But like my dad always said "Be not the first by which the new is tried, nor the last to set the old aside". Some how is sounded better when he said it the when I wrote it. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  13. #13
    Join Date
    Nov 2007
    Location
    Rochester, MN
    Posts
    80
    I'm going to return the fiber glass insulation I bought and follow this process
    http://www.rd.com/57548/article57548.html
    Thanks for the information.

    As far as my summer IAQ goes, last summer the temps got down to the high 50s and low 60s every night so we just opened up the windows and cooled off the second story. I think we ran our a/c less than a dozen times. I wasn't monitoring RH as closely then, and will do so this summer to see if I need to make any changes to my HVAC setup. However it never seemed uncomfortably humid like in our old house.
    -D in MN

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