Author Topic: Basics of a Forced-Air System  (Read 3073 times)

Offline cindymazz

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Basics of a Forced-Air System
« on: December 02, 2008, 06:22:55 PM »
Forgive my ignorance, but would like some impartial answers from experts please (and these are basic questions).  My house is 35 years old and came with a forced-air system, probably newer than the house(heat only, I live at the ocean).  My questions lie primarily with the issue of filters.  The filter at the unit itself "was the wrong size" - and currently has no filter.  Inside (I could use an anatomy lesson here), I have the standard floor registers in each room.  There are also two openings (ducts?) in the wall, in different rooms, which currently have no filters.  I'm assuming one of these ducts sucks in air, the other pushes it out.  What issues arise with the absence of filters?  Second question is with the current placement of those duct openings in the wall.  One is located behind a door (i.e., when the bedroom door opens completely, it is flush against the grated opening).  The location never made sense to me - is it a problem?  Otherwise I would have to keep my bedroom door closed when the heater is on, which is ridiculous.  The other duct opening has a small indoor fountain that partially obscures the grated opening, but not enough to prevent air going in or out.  Is that a potential issue (well, it might be if I'm trying to unscrew the grate to insert a filter). 
Thank you in advance for your advice! 

Offline Admin

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Re: Basics of a Forced-Air System
« Reply #1 on: December 02, 2008, 08:57:28 PM »
I wouldn't bother installing filters in each individual floor register.  Go down to the furnace and look for a filter rack that's installed between the furnace and the return air duct.
Installing a filter there is all you need.  If you don't have a filter rack just hire a heating contractor to install one.  Look at the different media filters that are on the market.  Lennox sells the HC16 filter that's 95% efficient.  It's a 5" filter that requires a special cabinet to be installed.  The filter itself is designed to last the year so it can cut down on filter costs in the long run.

You have no central a/c so you don't have to worry about the coil getting plugged with dust.  If your furnace is high efficiency there is a secondary heat exchanger coil that could get plugged with dust if there is no filter.  The blower itself becomes full dust that restricts air flow and can cause the blower to run off balance causing noise and eventually damages the motor.

If you're not spending time in the bedroom and the door is open restricting the return air grill I wouldn't worry.  If you're in the room I would close the door so the air can exchange and keep you comfortable.  Restricted return air grills can cause overheating problems with the furnace.  I would leave the door at least a couple of inches from the return grill.