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theguitarman
Connecting Ductwork
theguitarman

Hello,

I am working on some home improvements and I just don't know enough about ductwork to fix this issue. All of the ductwork in the basement feeds up through the floor and uses the plenums to move air up to the second floor, even using exterior walls (filled with insulation).

The first floor vents just have the duct work shoved into an oversized hole. Lots of dust and cobwebs and such around the openings, and presumably the air isn't going where it is intended.

My two questions are: what is the proper way to "transition" from duct to plenum/through the floorboards. Should I use foil tape to seal all the gaps, and then maybe Great Stuff to insulate it a bit??? I can't seem to find any good information on how to properly do this.

Second question, is that normal, to use exterior wall plenums which have batts of fiberglass insulation in them to move the hot air? That seems odd to me (home was built in 1979)

Thanks in advance

ordjen
Re: Connecting Ductwork
ordjen

I have seen the passages formed by the houses framing used as air returns, but never the forced air being sent through them in lieu of actual duct work. My former house used the framing cavity as the return duct. Unlike ducting, the return is under negative pressure and therefore sucks air inward if not sealed tightly. The hot/cold air delivery is under positive pressure and therefore is going to leak like a sieve if not sealed well.

In my former home, this return passage was an interior wall, not an exterior wall, although I don't know why an exterior wall could not be used if it were sealed and insulated. An interior cavity is at least leaking conditioned air to the house's conditioned envelope, although it might be adversely affecting the heating system balance. An exterior wall is conceivably leaking air to the house exterior and wasting energy.

FRANCO
Re: Connecting Ductwork
FRANCO

 

Mini-split HVAC systems offer several advantages if you’re looking for a home heating or cooling solution but your home doesn’t currently have ducts. Installing a mini-split system is a much smaller and less costly project than installing ducts, but can provide the same multi-room heating and cooling as a central forced air system. 

Mini-split HVAC systems offer automatic HVAC zoning capabilities without the problems associated with zoning a central forced air system, letting you choose to heat and cool only the spaces you are currently using to reduce energy consumption and keep your monthly bills as low as possible. 

The air handlers associated with your mini-split system can be installed in a variety of locations, including ceilings and walls, allowing for a versatile heating and cooling solution that can be tailored to each space in your home for the utmost convenience. 

These systems are quiet, unobtrusive, and won’t suffer from duct losses, which can rob a central HVAC system of efficiency over time. Over the years, most mini-split HVAC systems will lose less than 5% efficiency due to wear and tear, as opposed to duct losses that can rise as high as 40% if interior ductwork is not cleaned and repaired periodically.

HandyAndyInMtAiry
Re: Connecting Ductwork
HandyAndyInMtAiry

Yes, a plenum should be of an actual piece of duct work. And should be sized accordingly. If you have soft duct, have them all replaced with hard pipe. Seal each connection with duct mastic, foil tape over that and insulate the duct over that. I am a little confused about your sentence " proper way to "transition" from duct to plenum/through the floorboards" Ducts are branches off of the plenum, a plenum is a vertical main trunk that allows air to move from an air intake into the blower unit, or a vertical duct out of the blower unit of a forced air furnace. Horizontal ducts are just know as duct that feed smaller branches to the registers. But if your plenum is filled with bat insulation, that is just wrong. You will end up with no air pressure. My parents had one large furance in the basement that supplied the entire 3 story house. I own a 3 story Victorian house, but we have one small unit for each floor that resides on each floor. This works out very well with this type of configuration.

Andrew

Handy Andy In Mt Airy NC

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