A while ago, I posted about the function of cold air return vents for a forced-air furnace. I have written quite a number of posts about this issue, actually– I became interested in this topic when I decided to re-do some of my old furnace ducting myself, last year. You can read about that here and here.
Well, I got a question from a guy named Barry who lives in Vermont (a climate just like New York State).
In my old Vermont house, with an oil furnace, I’ve got two vents clearly, forcefully, blowing cold air out into the house. Because of this, it seems impossible that they are cold air *return* vents. How can I confirm that they aren’t? Second question: can the furnace itself have the only cold air return vent?
I wanted to post his question and my answer in a separate post, because I think it may do others some good, searching for more information about cold air return vents. Here’s my response:
Hi Barry. Well, I’m not a furnace expert, but what I’d do if it was me is this:
1.) Make sure your ducting system is set up right. If you look at your furnace (you’ll see all sorts of ducts leading everywhere), you’ll see an “in” large duct and an “out” large duct, with many smaller ducts branching off of those. That’s for most forced-air furnaces, anyway. Check and make sure you know where the ducting system branches off into, and become familiar with your furnace system.
2.) My hot air return vents ALWAYS blow out cold air for the final three or four minutes right before the furnace stops. This is because the furnace fan keeps spinning for a little while after the gas heating flames go out– this is natural, to ensure that all the hot air has fully pushed through into the room. It’s the normal part of the cycle.
3.) Maybe your hot air vents blow out cold air because they are either too far from the furnace (like a third floor) or you don’t have enough cold air return vents and the furnace is just blowing whatever air it can find (and in an old home in a Vermont winter, that would be cold air).
I hope those tips help.
When I first paid attention to my furnace system, I was baffled that cold air blew out of my heater vents. After asking my Furnace Guy, he informed me about the natural cycle of a furnace air system. I suspect this may be Barry’s thought, too. Some furnaces will blow and blow cold air for quite a few minutes before shutting off and completing the cycle.
So I hope this helps anyone who is searching for furnace answers.
Mon, Jan 5, 2009
HVAC