Forced air duct heating floorboards at entry - a waste?


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Old 02-14-07, 06:35 AM
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Duct heating my floorboards at entry - a waste?

My home is a 2 story Philly victorian dated to 1891 that has seen it's share of modifications over the years. I have two distinct generations of ducts/heat registers which I suspect were installed with both an old oil furnace and the current gas furnace (several original cast-iron registers and even what I believe are some portions of iron duct work are still in place!).

After my first two $300 gas bills (!!) I'm trying to bring the system into the 21st century and up to some level of efficiency. I currently have a 20-year old forced air gas furnace that was checked out and cleaned by a HVAC pro.

I've already sealed all the duct joints that I can reach with foil/duct tape and have purchased 'duct wrap' insulation for the main supply duct in my unfinished basement but have run across something surprising.

I've located a poorly insulated duct that appears to lead not to any vent or register, but rather right to the subfloor at my entry/foyer. Thus I have a duct soley dedicated to heating the floor boards!

Can I just seal/cap this thing off at the plenum and improve my efficiency? I can't imagine that this is a modern practice and the first floor is already fitted with five other registers/vents. (note - this is not a shoe-free household!)

Thanks,

Ross
 

Last edited by OldPhillyRow; 02-14-07 at 08:56 AM. Reason: clarification
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Old 02-14-07, 10:29 AM
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duct to floorboards

If that duct is coming off another duct, seal it off. Too much heat lose. If it is coming from the main unit by itself, don't seal it off, route it back into your duct system.
 
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Old 02-14-07, 01:16 PM
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Originally Posted by Duke of View Post
If that duct is coming off another duct, seal it off. Too much heat lose. If it is coming from the main unit by itself, don't seal it off, route it back into your duct system.


Thanks for the reply. Yes, I'm afraid this duct (about 4-5" diameter) is coming straight off the furnace itself (the plenum, I believe.) while the trunk (main supply, 8" x 8" rectangular duct) to the rest of the ducts in the house comes off of the other side of the unit.
The furnace itself is just a few feet from the front of the building (next to where the oil reservoir used to sit under the porch)


I suspect you suggested the above because sealing the plenum/furnace itself could pose a real challenge. However, rather than wasting more ductwork and time running this useless supply duct all the way around my furnace to reach the trunk, could I:

1. Leave perhaps a foot of this 5" duct extending from the furnace, being certain it's still secured to joists above.
2. Purchase a properly fitted cap for this duct
3. Douse it with mastic before I fix it on the end and cap off the thing?

Pardon me fumbling with new terms - I'm learning the HVAC basics quick!


Thanks again,
 
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Old 02-14-07, 03:04 PM
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Wink

to lead not to any vent or register, but rather right to the subfloor at my entry/foyer. Thus I have a duct soley dedicated to heating the floor boards!

If this is so then code could get you. No way can you have a heat duct just blow in a wood space that way. You can use a joist space like wood and use it for the return to the furnace. When you say basement. You are better to let warm air out down there it will help to heat the floor above. Might just let it open down there .Better off to put insulation on the outside walls .
 
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Old 02-14-07, 05:18 PM
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Originally Posted by Ed Imeduc View Post
to lead not to any vent or register, but rather right to the subfloor at my entry/foyer. Thus I have a duct soley dedicated to heating the floor boards!

If this is so then code could get you. No way can you have a heat duct just blow in a wood space that way. You can use a joist space like wood and use it for the return to the furnace. When you say basement. You are better to let warm air out down there it will help to heat the floor above. Might just let it open down there .Better off to put insulation on the outside walls .

Well - things are a little clearer!

After briefly unfastening the duct from the subfloor, it appears that one of the previous owners simply covered up an existing floor register with luan and new flooring. So, the duct was INTENDED to heat the foyer, though I'm not sure of the wisdom of a floor vent in such a high traffic area.

So, for the time being I'm just turning the duct itself and leaving it open to heat the basement and stairway to the first floor.

Regarding code, with all of our old buildings, Philly has an 'existing building' portion of our zoning/building code exempting many such properties from modern standards. (Not to mention inspectors are spread so thin that they only show long up after a collapse or other disaster!)

Insulating my walls: I've been weatherstripping and caulking windows like mad since this October (new double-hung, double-pane windows, but very poorly installed), but I don't believe I'll have many insulation options without completely gutting the place.
I've got plaster & lathe walls poised just 3/4" off of a solid brick front and rear. We'll get it right someday - hopefully without tearing out or covering up all of the original features! I'll hit up the energy/weatherization forums for ideas.


Thanks for the help folks,

Ross
 
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Old 02-15-07, 05:57 PM
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DUDE!!! a 20 year old furn in good working order is still only 40-60 percent eficient .save the money from the quick fix crap and get a med to high efficientcy furnace .you could cut your gas bill by almost half just by getting a new furnace ..not to mention if your heat exchanger lets go and starts blowing hot sparks or flaming lint into that open joist space youll be gettin a brand new house from insurance
 
 

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