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Air Exchangers w/ Radiant Systems

GMcD Member Posts: 477
"Humidity Control" means to control the indoor humidity by either removing excess humidity, or adding humidity, as required by the climate zone the house is in. During the dry winters, the humidity in a house should not be less than 30% RH for the lowest limit of healthy humidity. Below that threshold, there will be increasing problems with dry skin, cracked lips, dry nasal and lung passages, static electricity etc. etc. If the humidity in a room/house/building is not kept in that 30% to 65% Relative Humidity range, then there will be increasing risks of problems for the occupants.


  • Big Idahoan_2
    Big Idahoan_2 Member Posts: 3
    Air Exchanger w/ Radiant System

    We are working with a contractor who is building very tight, energy efficient homes. He is spraying urethane in the walls and there is minimal air exchange in his homes. Has anybody had a problem with stagnant air in this type of home. Do you think an air exchanger is necessary? Thanks in advance for the info.
  • GMcD
    GMcD Member Posts: 477
    The three legs of the stool

    A radiant system in a tight house is only one leg of the stool. Without the other two (ventilation and humidity control) the stool falls down. A tight home with solely radiant heating MUST have a ventilation system to provide healthy air exchange as well as humidity control. In many areas, a minimum air change rate is required by Codes. While the Codes require anywhere from 0.35 to 0.5 air chnages per hour, if it were my home and knowing what I do about human comfort and health, I'd be using at least 1.0 ACH, and this could vary depending on your local climate zone. Remember, the Code is the Minimum standard, and it's perfectly fine to use more than the Code. Too many people see the Code as the Maximum standard to achieve, which is not the right direction.
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    That's why the call it hVac

    You build up both humidity and indoor pollutants if you don't ventilate. For indoor pollutants, you can use a HRV or ERV to save some of the energy loss of ventilation. I prefer to run them slower and longer since it uses less power. Some have mentioned not running them during peak heating demand to cut their loss.

    For the humidity, I like humidity sensing exhaust fans in baths, well designed kitchen hoods, etc. These require there be some place for air to come back into the house (make up air.)

    .3 air changes per hour for outside air ventilation is a common target for residential situations. This doesn't count the ach from heat loss calcs, since that is variable and you need this all the time.

  • Bob_51
    Bob_51 Member Posts: 6
    Residential Ventilation.

    We use 10 cfm/room except for master 20/cfm or if there is a large unfinshed part of the basement, which could be later renovated to seperate rooms. Most houses built today will give you from 100-130 cfm load for high speed. Although not perfect by any means I find this a little more acurate in for our climate in Canda. 1ACH for a 2000 sq ft. home is 267CFM, a little too high, .3 is alittle more realistic number. Although there is nothing wrong with too much fresh air. If we over ventilate the consumer may just turn it off bacause of percieved addition to the energy costs. But If I designed my home from scratch. I would be a little smaller for the HRV and use Bath and Kitchen Range hood fan's to do the bull work. Works a little better for our climate our design temp is -12 F. But as is anything the most important part of any rule of thumb is knowing why we do what we do. So we can allowe for any customer's unique requirements. For example, I could get myself in trouble using my rule of thumb with some of the open concept homes if I just knew the rule of thumb but not the why I use it.

    Good Luck,
    Moncton, NB
  • Dirk Wright
    Dirk Wright Member Posts: 142

    As others have said you need at least one HRV or ERV, depending on your location. You need more ventilation if you have combustion appliances (boiler, water heater) that are not directly vented, and if the clothes dryer is within the conditioned space. You also need more if you are using gas for cooking and/or have a fireplace of some kind. Add in things like a central vacuum cleaner and more than the normal number of bathroom exhaust vents and one HRV or ERV may not be enough.
  • JohnWood1
    JohnWood1 Member Posts: 63
    HIGHLY neccessary.........

    Unless you want to breathe mold, mildew, formaldahyde and other nasty things........ not to mention that a tight home without ventilation will likely stink.

    As to the rate of ventilation. .34 is the "official" rate for healthy living. I tend to use a HRV with a higher rate available and run it on a slow speed continually. Some good HRV's have 5 sppeds to choose from and an integral dehumidistat. This will kick the unit into high gear when the humidity climbs beyond your setpoint. Very handy for folks who seem to "forget" to turn on the bath fan! Oh; and speaking of bath fans....... with a HRV you don't really need 'em. Just have the HRV take the stale air from the bathrooms. Quiet... efficient.... balanced ventilation. Had a customer call and thank me for installing one in his new home. Said he was frying fish and within 15 minutes you could not tell! Love positive feedback. In N ID you wil need to use a HRV and not an ERV due to feeze damage. also make sure your HRV has a positive damper defrost, otherwise it will be MUCH less efficient and will unbalance the homes pressure while in its loooong defrost cycles.

    Have fun!
  • Big Idahoan_2
    Big Idahoan_2 Member Posts: 3
    We don't have any humidity..

    We live in a very arid part of the country. most of our humidity concern is for the lack of humidity. Would you guys install a humidifier?
  • Constantin
    Constantin Member Posts: 3,782
    An HRV or ERV is a very good idea...

    ... though some projects have done as little as put in properly-sized bathroom exhaust fans that are balanced with intakes. I would take a look into the designs at Building Science Corporation for the "Building America!" program. Lots of great tips on how to improve energy efficiency without spending a mint. Home Energy magazines has also published numerous articles on how to deal with ventilation cost effectively.

    I would install an HRV/ERV, but that's because I'm an energy-efficiency advocate.

    Lastly, take a close look at all the appliances in the home that need combustion/make-up air. For example, kitchen hoods are notorious for sucking vast quantities of air out of homes, so one has to be careful on how to design the make-up air into the system.

  • Whoa, Geoff, that's a rate waaaay over any standard I know of, including ASHRAE's. Do you know something they don't? You aren't running that exchange rate continuously, are you?? I mean, especially if you are doing humidity control such an exchanger rate would dramatic upsize your humidity control requirements, wouldn't it?
  • GMcD
    GMcD Member Posts: 477

    The humidity levels I've stated came from ASHRAE standards as well as numerous health studies. If you check out the Building Science website, among many others, the upper limit is usually 70% RH indoors, since increased mold growth potential will occur, and the old ASHRAE lower limit was 25% for human health. The current ASHRAE standards don't really come right out and state a specific range, and leave it ambiguous as to what the "design standard" should be. I did a lot of research for the short article I wrote at Healthy Heating and the references are all there. (see the Coast2Coast reports section).

    The run-time of the HRV/ERV and humidity control will be dictated by the local climate, and indoor conditions that add to, or affect indoor humidity levels. Yes, in hot, humid climates, the house ventilator should be sized for either humidity removal, and healthy ventilation, whichever is greater.
  • JohnWood1
    JohnWood1 Member Posts: 63

    You said you are building TIGHT houses! In this case it does not matter what the external humidity is (for heating) as your latent load is internally generated. If it is necessary to keep some controlled humidity inside the home, run the HRV in the recirc mode on constant low speed and let the internal dehumidistat and a bathroom timer control the ventilation/ dehumidification.

    One side note; lifebreath now is producing a TRV (total recovery ventilator) with both a HRV and an ERV core for locations with climates of moderate humidity to control the humidity gain in cooling season.
  • GMcD
    GMcD Member Posts: 477
    Heating mode

    But in a tight house with exhaust from kitchen, bathrooms and fireplaces (if not using sealed combustion units) then outdoor air has to be introduced into the house for make-up air anyway. If the outdoor conditions are cold and dry enough, even that rate can cause low humidity inside the house given the right conditions.
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