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  1. #1
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    Fresh Air with separate AC & Heating Systems?

    I have been reading various threads on fresh air ventilation and utilizing an Ultra-Aire whole house dehumidifer.

    But, what if you have an A/C system w/ductwork in the attic and a separate Forced Air Heating System & ductwork in the basement? Hooking up the Dehumidifier to the Attic would help to reduce humidity in the summer and then provide fresh air. But then what to do in the winter or fall/spring when you may not need heat or AC?

  2. #2
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    Thanks for the interest in indoor air quality and comfort. I assume we are talking about a green grass climate along with below freezing winters? Humidity control is a 3 season problem mainly. In most homes, mechanical fresh air is 3 season plus calm winter winds problem. Basements are also in need of dehumidification. The ducts of heating or cooling systems will work for distribution of dry fresh air with emphasis on the basement.
    It would be good to be out of the attic for concern about freezing.
    All things considered, basement with fresh air to the dehumidifier and connection to the heating ducts sounds most practical in this case. Also a tee with dry air to the basement seems in order.
    How is this for starters?
    Again thanks for interest in a most important part of a homes issues, indoor air quality and comfort.
    It cost a little more but gets you and your home a longer life.
    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"

  3. #3
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    Thanks bear,

    Yes Green grass climate and freezing winters. That's what you get in NJ.

    Just a couple of particulars and questions. Basement is mostly finished, except for utility room. There are heating ducts in the basement, although I think they all may be closed off. There is a return in the basement, which I am thinking should be eliminated. There is Radon, but with the remediation fan its ultra low and way below threshold.

    So as far as hookup, Am I then just ducting a dedicated return in the basement to the dehumidifier?
    There is a duct that runs outside to pull in fresh air.
    Then I assume the supply side off the dehumidifier goes into the supply side ductwork off the furnace using the dehumidifiers fan? My furnace has two branches off the plenum. One runs through the basement in my split level and supplies ducts for the main level (Kitchen/DR/LR) The back of the plenum goes up through the garage and supplies the bedrooms, Laundry room and family room).

    Do I need to T off the supply side of the dehumidifier to the basement if there are supply ducts off furnace trunkline?

  4. #4
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    If your heating supply ducts are open to the basement, connecting to dehumidifier to the supply ducts will do. If the heating ducts are closed to the basement, tee off the dehu supply to the basement will work. If the finished part of the basement is open to the rest of the home via a stairway, the return from the finished part of the basement to the dehu works. If the stairway is closed, a return from the open part of the to the dehu works. The idea is get circulation of dry air throughout the home. The dehu fan will circulate the dry throughout without operating the furnace blower.
    keep us posted.
    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"

  5. #5
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    Quote Originally Posted by teddy bear View Post
    If your heating supply ducts are open to the basement, connecting to dehumidifier to the supply ducts will do. If the heating ducts are closed to the basement, tee off the dehu supply to the basement will work.
    Got it for the supply.

    Quote Originally Posted by teddy bear View Post
    If the finished part of the basement is open to the rest of the home via a stairway, the return from the finished part of the basement to the dehu works.
    Is that a dedicated return to the dehumidifier or connected to furnace return? Basement has a door to upstairs. typically closed.

    Quote Originally Posted by teddy bear View Post
    If the stairway is closed, a return from the open part of the to the dehu works.
    ?? Not sure what you meant to say

  6. #6
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    My mistake. Closed stairway, suggest a return from the mainfloor of the home to the dehumidifier. When using fresh air, a return from a clean source of outside surface. The mainfloor return and fresh air return are combined into the dehumidifier. A electric damper/balancing damper in the fresh air return is suggested.
    The open part of the home return allows circulation of the air in the home through the dehu via furnace ducts back to all parts of the home.
    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"

  7. #7
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    Is that a dedicated return on the main floor to the dehumidifier or just connect the dehumidifier to the return side of the furnace, to pull air in that way?

    I got fresh air - Clean source from the outside (i.e. a min of 10' away from any exhaust vents). Will probably put this right in the front of the house.

    As far as the electric damper/balancing damper do you have any recommendations. Figure it has to be one that seals w/ gasket to ensure it stays closed and no air leakage.

    Got the connection back to the furnace supply ducts and possibly with a T to the basement if I kept the supply ducts closed here.

    Add Questions:

    -Not that the basement is musty but should there be air pulled from basement as well for dehumidification? Current setup seems like it would just pull air from main part of house. Have to check in the 3 seasons but think humidity level is higher in basement then rest of house.

    - I get the dehumidifying air in the 3 seasons (fall/winter/spring) and how this works cause the furnace is off. But you had also mentioned also doing this the winter when home is occupied. At this time the furnace would be operating. Not sure how this affects the way the dehumidifier works if the furnace is running. Also, we have a humidifier hooked up to the furnace, cause in the winter the humidity level is very low. Figure the dehumidifier is set to 50% or maybe under that. Never is that high in the winter anyway so figure the dehumidifier would never kick on but assuming then fresh air would then be pulled in somehow? Not sure how that works if the dehumidifier isn't dehumidifying.

    - I know the system pulls in outside air for ventilation but unlike and HRV/ERV it doesn't remove the same volume or air back out. Not a concern?

  8. #8
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    Quote Originally Posted by imt View Post
    Is that a dedicated return on the main floor to the dehumidifier or just connect the dehumidifier to the return side of the furnace, to pull air in that way?

    I got fresh air - Clean source from the outside (i.e. a min of 10' away from any exhaust vents). Will probably put this right in the front of the house.

    As far as the electric damper/balancing damper do you have any recommendations. Figure it has to be one that seals w/ gasket to ensure it stays closed and no air leakage.

    Got the connection back to the furnace supply ducts and possibly with a T to the basement if I kept the supply ducts closed here.

    Add Questions:

    -Not that the basement is musty but should there be air pulled from basement as well for dehumidification? Current setup seems like it would just pull air from main part of house. Have to check in the 3 seasons but think humidity level is higher in basement then rest of house.

    - I get the dehumidifying air in the 3 seasons (fall/winter/spring) and how this works cause the furnace is off. But you had also mentioned also doing this the winter when home is occupied. At this time the furnace would be operating. Not sure how this affects the way the dehumidifier works if the furnace is running. Also, we have a humidifier hooked up to the furnace, cause in the winter the humidity level is very low. Figure the dehumidifier is set to 50% or maybe under that. Never is that high in the winter anyway so figure the dehumidifier would never kick on but assuming then fresh air would then be pulled in somehow? Not sure how that works if the dehumidifier isn't dehumidifying.

    - I know the system pulls in outside air for ventilation but unlike and HRV/ERV it doesn't remove the same volume or air back out. Not a concern?
    Prefer a dedicated return from the main floor of the home. If you draw from the furnace return and blow into the furnace supply, some dry air flows through the furnace and returns to the dehu without passing through the space of the home. It this is difficult, you could draw from the cold air return and supply the basement dry. This will cause circulation also.

    Does this mean you already have fresh air inlet?
    If not, we have a electric damper that will respond to the ventilation time in the DEH3000. YOu have enough air leakage and needs to not be concerned about the air exfiltrating. Also clothes drier and bath fans need make-up air.
    If you already have and ERV disregard the fresh air discussion.
    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
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    Quote Originally Posted by teddy bear View Post
    Prefer a dedicated return from the main floor of the home. If you draw from the furnace return and blow into the furnace supply, some dry air flows through the furnace and returns to the dehu without passing through the space of the home.
    Wouldn't this also happen if you had a dedicated central return on the main level to the dehumid with the Unit exhausting into the HVAC supply ducts? Thus any air coming out of supply on main level could potentially end up back to the dehumid?

    I don't currently have an HRV/ERV or vent into the house. My only vents are the leaky parts of the house that need to be sealed up. You had mentioned in the previous post about the need for an electronic controlled damper for the inlet. So I didn't know if that was a part you offered or if I needed to obtain elsewhere.

    However, I do have another post here, with no comments yet, on makeup air for my rangehood. I have been trying to find a perfect solution to that for years. There is a variable speed blower on the 1200cfm or 1400cfm hood. I think on low it could be around 600cfm. Not sure if I can crank down the lower limit. Exhaust is connected to a 10" duct. In theory I think I should have another 10" duct connected for make-up air and dumped in the house. Haven't figured out the best approach for that but probably needs to be factored into this equation/plan

  10. #10
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    Quote Originally Posted by imt View Post
    Wouldn't this also happen if you had a dedicated central return on the main level to the dehumid with the Unit exhausting into the HVAC supply ducts? Thus any air coming out of supply on main level could potentially end up back to the dehumid?

    I don't currently have an HRV/ERV or vent into the house. My only vents are the leaky parts of the house that need to be sealed up. You had mentioned in the previous post about the need for an electronic controlled damper for the inlet. So I didn't know if that was a part you offered or if I needed to obtain elsewhere.

    However, I do have another post here, with no comments yet, on makeup air for my rangehood. I have been trying to find a perfect solution to that for years. There is a variable speed blower on the 1200cfm or 1400cfm hood. I think on low it could be around 600cfm. Not sure if I can crank down the lower limit. Exhaust is connected to a 10" duct. In theory I think I should have another 10" duct connected for make-up air and dumped in the house. Haven't figured out the best approach for that but probably needs to be factored into this equation/plan
    Drawing air from the mainfloor and supplying dry air through the furnace ducts passes through the home to the dehu return. The results is a dry home.
    Dealing with a high capacity exhaust hood is a different problem. I was at a conference last that suggested fresh air supply from outside to the kitchen stove area that had a 50% make-up air flow. I have not tried this yet. opening a window or screened patio door may work?
    Keep us posted.
    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
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    Now I have another humidity issue to tackle. This involves the area under my front porch. See pics below.

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    These pics were taken this Am at 9am. You can see the humidity level is already at 54%. Probably around 40-45 Degrees then and will hit around 60 today.

    I have seen this number go up to over 60% and maybe even over 70% in the summer.

    Now, originally this area had no encapsulation and just a gravel floor. I knew from the humidity levels and condensation in the winter, on the underside of the steel corrugated decking closest to the thin steel door, I had to do something if I ever wanted to use this area for storage. I then encapsulated the area this past summer. After the install, I took rigid foam and weather stripping and made a panel that sealed the opening closed behind the steel door. I know when I was inside the space and set that in place, you could see no daylight.

    I then borrowed a friends dehumidifer on wheels and turned it on to dehumidify the space. When running it seemed like it was removing humidity. The levels on the units meter and even my own showed it dropping to acceptable levels. There really was not much water collected in its tray. When I turned the unit off and with the door area sealed up. the humidty would rise. The company where I bought the vinyl encapsulation barrier from thought that it may be humidity coming in from the areas of the wall unexposed, since there was what appeared to be efflorescence on the top area of the wall in spots. Since the corrugated decking sits on top of the outside wall, you can see the cultured stone, in the "up" sections of the corrugated decking. I also know that the concrete block is hollow (i.e. holes were not filled with cement) Evident when I drilled for the new hose bib. So either water is leaching into the holes or more likely, water is wicking up the wall, primarily on the outside and when heated up is maybe pushing its way inside. Especially later in the day when hit by the sun (Faces West). NOTE: While the concrete block itself is not filled, the top of the block is capped with flat concrete pieces, then the corrugated steel sits on top. Above the corrugated steel I believe is concrete and then they put down sand and pavers.

    So thinking of running the encapsulation all the way up to the top of the wall on three sides (Excluding the house side). Maybe then spray foam the open areas/sections in the corrugated decking on top of the block wall. Thinking that this hopefully will seal any moisture out and prevent any diffusion into the area. Don't know if anything can come through the top/corrugated steel. Wouldn't think so and no moisture has ever leaked through where the sections overlap. I also can foam the other side, in which the corrugated steel sits on top of a steel L beam. I then figure that this space probably then needs to be dehumidified right? Area obviously isn't huge so what may be the best approach?
    Last edited by imt; 03-11-2015 at 01:14 PM. Reason: Rotated pics

  12. #12
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    If any high dew point outside air gets in the space, the space may be damp. A little dry air from the dehumidifier in the home would take care of the problem. Or not store anything that would be affected by the dampness. Tighten up as much possible and wait for summer outdoor dew points. A small amount of heat in the space could also do the trick. Operating a space heater when the space %RH exceeds 60%RH could do it. An cheap dehumidifier in the space could do the same thing.
    Keep us posted on your monitoring.
    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
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    Thanks Bear.

    I haven't really used this for storage, sans the extra hardiplank, cause of the humidity. I would like to use the space. I do think the encapsulation has made a difference cause I did not use the rigid foam piece at all and checked when it was freezing out. No visible moisture (i.e. raining from steel decking) like had been the case in the previous years. Also, the space was now cool 30 degree or mid 30 degree range when it always was warm in the past. So that has to be keeping out the ground mixture anyway. I used to just leave the door open many times in the winter so it would dry it out.

    I see one solution was to pipe in some on the dehumid air from the house system to this space. No concerns with piping to what amount to an enclosure outside the living space with the duct running back into the living space? The utility room is actually on the other side of the original house wall, towards the back (away from opening). Also, would
    't that then lead to depressurization of the house somewhat?

    I am having a hard time wrapping my head about how dehumidification works. I would have thought you need to pull air direct from the moisture area to then dry it out. But in this case one of the recommendations was just to pipe in some dry air. Similarly, if the basement in a house had the highest humidity, I would have thought you need to pull the air from that area to drop the humidity level. Guessing then that just mixing dry air with the humid air cuts the level overall?

    I will try and seal the under porch area some more and see what happens. The issue with a smaller cheap dehumidifier is the noise could be an issue, not to mention the units stand tall and typically all blow air out the top. Don't forget having to then manually drain the water cause the unit is sitting on the floor and no where to then plumb it to, if a model even has that feature. Not that I'm looking to spend over 1K on a santa fe or ultra-aire but those are more designed for the horizonal intake and exhaust but are probably way overkill for the space due to the volume of space they can typically cover. Hmmm.

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