Don't know for sure but are you talking about an air exchange ventilator in your attic? If so, these are usually set up to operate continuously, that is, always drawing air off of the house and always bringing fresh air into the house. Most have a high and a low speed, the high speed kicks in when the humidity goes above some pre-set level or, in the case of my set-up I also have timed switches in bathrooms which bring up the higher speed.
These days most such ventilators include heat exchange units, I don't know how common that is in the United States particularly further south. The cores do vary, some are higher efficiency than others particularly important where you have bigger differential heat gradients. The air streams pass eachother but do not touch so, the incoming stream picks up heat (or cool) from the outgoing stream. The efficiency falls as temperature gradients grow. Here for example, at minus 40 there often isn't enough heat recovered to defrost the heat exchange core so at intervals the ventilator goes into a defrost mode which feeds some of the air back through and includes an electric heater to defrost the core from freezing condensed humidity in the exhaust stream. So, if this is your situation it is true that the ventilator is bringing fresh air from outdoors into your home. This will be cooling the home in the winter and warming it in the summer. If the unit includes a heat recovery core then this is mitigated to some extent and the dehumidification probably cheaper than running a dehumidifier big enough for the entire house. With the more air tight homes now the advantages of exhausting off-gasses from building materials and other household products along with the introduction of fresh air is necessary and all help to keep the growth of molds and other spores down. Hope this helps. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: Matt To: [email protected] Sent: Thursday, January 17, 2008 1:38 PM Subject: [BlindHandyMan] Back drafts up furnis air intake? Hi, I live in a house, have all electric central heat and air. Currently it is set to heat, the switch which is for auto, or fan on is set to auto, and heat is on. Here's what I noticed, just because I happened to be standing under one of my air intakes earlier. I noticed a sort of back draft, of air going up through that intake, but the unit was not currently running. I noticed it happened a couple of times. What causes that? Seems like it would be sucking warm air out of my house and/or causing these cold drafts inside and I don't care for that idea. Is that normal? Do I need to check something? NO windows should be open in the house, and this intake I noticed this problem with is the one inside the house itself. The main unit is up in the attic, and we have two intakes. One is actually in the garage because I have a vent out their to keep it somewhat heated and cooled as a shop. Thanks, Matt [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
