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Heating & Air Conditioning

Dryer vent ducting to heat garage...enhancements

17 years ago

My dryer vent duct runs through my garage and out through the outer wall, it provides a surprising amount of heat considering, and I've been wondering if I could improve it further, by:

-Extending the duct so it runs through the garage more, say, by adding a couple of turns

-Using aluminum concertina ducting - more surface area for one, like a radiator fin, and I believe aluminum has better heat conduction than galvanised steel

-Painting the outside of the ducting with an appropriate black paint

-Adding a damper/door arrangement on the inside of the outside wall, before the pipe exits the wall - it does have a self-closing door on the outside, although condensation and dust sometimes stops it from closing. During really cold weather, I get frost buildup on the inside foot or so of pipe. This damper is made specifically as a second self-closing device to reduce cold ingress.

I have heard talk of a maximum of 14 feet for dryer ducts. I'm in British Columbia so this may not apply - I'm assuming this limit is to reduce possible condensation problems if the air's allowed to cool too much - and i wonder if this could be a problem with what I propose to do.

Condensation's one of the reasons I was considering changing to the aluminum ducting, it should resist corrosion better. I do wonder if there's a fire code issue with aluminum vs steel as it will buckle and melt at a much lower temperature, and it will be in a garage, after all.

I assume the theory with black paint on air-cooled engines, heatsinks etc is the paint absorbs heat from the metal, thereby encouraging more heat from the air going through. The second damper should in theory discourage heat loss...if it restricts air flow somewhat, I should see more heat extraction, provided it doesn't create problems elsewhere.

Any thoughts on this? In order to instal this damper, I'll have to cut the existing duct anyway, which I think may leave it too short, so I figured while I'm at it, I might as well try some of the other mods.

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Comments (6)

blacknumber1
17 years ago
Most codes only allow two turns in a run of dryer vent. I wouldn't go around re-routing the vent. They do make special heat reclaimers for dryer vents. Aside from that, the only theory that doesen't sound too hairbrained is flat black paint.
funnycide
17 years ago
The length and elbow restriction is mainly to keep the velocity high enough so it exhausts the lint. You don't want the lint to build up in the duct where it could block the airflow.
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DNT1
17 years ago
Is this a Gas Dryer? If it is electric I would install a diverter and filter box and let it simply dump heat into the garage during cold weather. If it is a gas dryer you cannot vent inside since the exhaust contains combustion byproducts and could kill you dead very quickly. You can probably find a inline heat exchanger box for a gas dryer but not sure they really do much good since it has to have a electric blower fan on it to be effective. Are you maybe thinking about starting a laundry service? I work out of town a lot and use the laundry service a bunch. Most places charge around $1.25 per pound wash and fold service, you could heat your garage and make some cash also!!! IF you dont mind handling other peoples DIRTY SOCKS and UNDERWEAR LOL
pjb999
Original Author
17 years ago
Umm thanks blacknumber, I think...(re the hairbrained)

Funnycide, you make a good point re the lint. I certainly wouldn't want it building up in there, so you wouldn't want too many sharp turns, either. That far it wouldn't be as much of a fire hazard, but if it blocked, it would certainly be a hazard.

If it wasn't for the damp problem and the other reasons that make those warm air diverter things a bad idea, that'd be the answer, apart from the fact they don't work (and I don't want a garage full of dust)

Even if the heat's not excessive, I'd use some sort of fireplace paint if I paint the duct...funny that, why's flat black more effective? That's what I'd heard, anyway.

Downside of the ribbed/extendable aluminum ducting is the tendency for dust to collect, I suppose. If I'm prepared/able to clean or vacuum it out periodically, I guess that wouldn't be a problem.
blacknumber1
17 years ago
The black paint works the same way as you can feel heat pouring off freshly laid ashphalt on a hot summer day. I don't think corrugated aluminum will give you much better heat transfer, and besides the stuff is a PITA to work with. All joints in dryer duct should be connected with aluminum tape and big hose clamps rather than screws, screw heads collect lint. And you should shop-vac out your dryer duct system about once every two years.
airsome
17 years ago
For long runs, go with galvanized steel (sheet metal) "conductor" pipe, nice and smooth on the inside. It comes in 10-foot lengths. For elbows see dryerbox.com.

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