Thanks for the replies to my first post.
I want to run ductwork into my soon to be remodeled basement. I can figure out how to get the hot air in through a ceiling register.
My question is about the cold air return. Can I add a louvered opening near the floor, venting to the unfinished part of the basement? Can I use a ceiling register (far away from the heat input) that ties into the existing cold air return plenum?
Or is there a better / proper way?
TIA,
Hippster
Replies
Basements are tough layout for distribution and returns. Since you are likely going to dump distribution air out of the ceiling, I would place the return airs near the floor and away from the supplies.
Dave
I hope Tim jumps in with some of his good info - until then a couple of potential concerns: returns shouldn't be too close to the furnace because they could depressurize the area around the furnace and cause backdrafting, and you generally need to consider not creating a negative pressure in the basement, so the returns have to be properly sized in relation to the supply registers.
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
Who, me?
Well, I'll give it a shot. Depending upon your basement layout, you might be able to run some big flexduct (14" or so) from your existing CA return to a grille low in the wall in your finished area. Ideally, the cross section area of the CA duct should be at least as large as the total of the cross section area of your output supplies.
Tim, can you are Bob explain the depressurizing thing Bob mentioned in his post?
Dave
Dave -
My understanding:
First: the furnace blower "pulls" air through the return air ducts and "pushes" it through the distribution ducts.
If there is an opening in the return duct too close to the air handler, it will pull air from around the furnace and reduce the air pressure there. That might be sufficient to overcome the stack effect in the flue gases so that they don't properly vent from the house.
That's why newer furnaces have the disconnect switch on the blower compartment door.
There are various rules on placement of return air ducts depending on whether the furnace is in a "confined" space or not. General rule - no closer than 10 in an unconfined space, no openings in the return in a confined space
Second. All houses have pressure zones arising from the fact warm air rises. That tends to create negative pressure in lower spaces (such as basements and crawl spaces.)
Over the years I have tested various scenarios during carbon monoxide testing: opening and closing cellar doors, exterior doors, garage doors; Turning vent fans on and off; opening and closing blower compartment access panels; to see what kind of effect they would have on the draft as measured by a draft gauge.
I have not found any consistent pattern.
In some, but not all cases, any one of those actions might significantly affect the movement of the flue gases through the flue (increasing it or reducing it or actually leading to backdrafting.)
Weather seems to also have an effect.
An expereinced HVAC tech can balance these concerns and do actual draft tests to confirm performance.
_______________________
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
Thanks Bob.