Found a puddle of water in my cupboards.

[Guido]

Not sure what forum to put this in, but here goes...

In my basement I have a range vent fan exhausting to the outside. The ducting is about 24-30 inches total length. I'm using

flexible ductwork - the metal kind (not the foil kind) and the water leaks right through the ducting (at the many seams).

Whenever it's really cold (less than -20C) the humidity in the inside air condenses inside the ducting and drips inside my

cupboards. It's not coming from the outside because the vent is under a carport - protected from rain.

Any suggestions how I can stop this from happening?

[bmwpower]

How about a "check valve" of sorts? You would need to keep the cold air out of the vent in order to avoid the condensation. The only way I can think of doing it would be to install some sort of diaphragm in the vent that would not allow the cold air from the outside back into the venting system.

Insulating the inside ductwork (so that the cold air never comes in contact with the warm air in the house) might work, but I'm not positive what you would use due to the high heat developed from the range.

[Guido]

How about a "check valve" of sorts? You would need to keep the cold air out of the vent in order to avoid the condensation.
I believe something like this would work perfect, but I don't even know if it exists. I checked a nearby hardware store and they didn't have anything.

Insulating the inside ductwork (so that the cold air never comes in contact with the warm air in the house) might work, but I'm not positive what you would use due to the high heat developed from the range.
I thought of this but I'm not sure if it'll work because I believe it's the air inside the duct that's condensing. The fan blows it up where it hits the cold outside air, then it condenses inside the pipe and leaks through the grooves in the flexible pipe. That's what I think is happening because it only happens when the fan is on. I'm afraid if I insulate it the insulation will only get soaked.

[Mr Fixit eh]

There should be a hooded flapper where the vent exits the building. I would imagine this flapper has broken off.

Try this link for a better vent hoodhttp://www.cetsolar.com/dryervent.htm These are available in Canada at both Home Depot and Canadian Tire stores. I've never used one with a range hood. You would likely want to clean it regularly to prevent build up of grease.

[Guido]

I bet for sure that'll work. But damn! Why do they have to make them so huge and ugly? I don't have much walking space at the side of my house as-is, and I'm sure that'll make it worse. But I won't knock it until I see it - I'll check out HD.
Thanks man!

[Mr Fixit eh]

I've used it on every dryer I've ever had--3 houses. It makes a difference.

I know your's is a range, but same principle. You'd just have to check for grease build up from time to time.

[Guido]

I took a better look this morning at the exterior vent. It's one of those aluminum ones (I believe one-piece with the pipe). Anyway, I looked inside and there is no flapper at all, just a wire mesh (I assume for critters). Maybe if I replace it with a plastic louvered one it'll stop enough cold air from going inside.

[Mr Fixit eh]

That would be a good first step. They're dirt cheap. And it will probably stop most of the condensation.

[Wgoodrich]

Be sure to use a vent listed and labeled for use with a range not a dryer. Dryer vents are not normally approved for use with a range. Fire of range hood system is much hotter rating than dryer due to grease build up expected in hood. Also the flex pipe is not listed for use with a range vent hood system.

See following Code rules;

M1502.1 General. Range hoods shall discharge to the out-
doors through a single-wall duct. The duct serving the hood
shall have a smooth interior surface, shall be air tight and shall
be equipped with a backdraft damper. Ducts serving range
hoods shall not terminate in an attic or crawl space or areas in-
side the building.
Exception: Where installed in accordance with the
manufacturer's installation instructions, and where mechan-
ical or natural ventilation is otherwise provided, listed and
labeled ductless range hoods shall not be required to dis-
charge to the outdoors.
M1502.2 Duct material. Single-wall ducts serving range
hoods shall be constructed of galvanized steel, stainless steel or
copper.

COMMENT;

My thoughts are you have the type vent hood outside that has a hood cap using the principle heat rises and cold settles thus limiting the cold entering your ducting. Problem is I am suspecting your hood outlet is exposed to cold winds blowing up into the hood causing the cold air to condensate. This can be cured by an installation of a flapper style closing the hood unless the hood is on blowing open that flapper style hood cover.

HOpe this helps

Wg

[Jacksnap]

My thoughts are you have the type vent hood outside that has a hood cap using the principle heat rises and cold settles thus limiting the cold entering your ducting.

Does this type of cap qualify as meeting code requirement for backdraft damper? The cap is shaped like a fish hook; right?

[Guido]

Here are some photos I found on the net.

The metal vent - that's what I have, except with a mesh underneath. But there is no flapper.

I'd like to replace it with the plastic louvered type - is that unacceptable?

The aluminum flex pipe is what I have. It's not the foil paper one wrapped around a wire, it's the rigid one that you can't easily crush, but you can flex it. That's no good? Are you saying I should replace it with rolled sheet metal ducts and elbows?

[Wgoodrich]

The flapper underneath acts as a draft stop preventing cold air from readily entering a warm duct causing condensation. This I believe you need.

The plastic hood is not to my understanding approved for use with a range.

The flex I see makes me believe it does not have a smooth interior wall as required.

Smooth interior wall of the duct and a back draft damper is required for a range.

If the hood vent catches a grease fire and an open damper is installed you have cold seeks heat feeding a fire already dangerous being a grease fire. Bad combination. The smooth inner of the pipe limits grease build up in the venting system where a ribbed inside will more readily catch grease inside the pipe.

Reread the copied code rule I supplied. That is a copy of the rule as written in the International Residential Code.

Good Luck and be safe

Wg

[Guido]

OK, I may as well do it correctly. I don't think replacing the flex pipe with regular ducting will be much of a problem, but I searched Google for 15 minutes and can't find any mention to a range-specific vent. The only one I found exited through the roof.
Anyway, I'll ask at Home Depot.
Thanks!

[Mr Fixit eh]

I would NOT take ANY advice I got at Home Depot. They are taught to sound knowledgeable, but they usually are dead wrong.

[bmwpower]

Have to agree there. Even I don't take advice from Home Depot anymore.

[Guido]

I agree with you guys too. The misinformation I received from them is incredible (and dangerous!).
I'm just going to ask them if they have range specific vents. I don't ask them any "how to" type questions

[Mr Fixit eh]

Let us know what you found out please.

[Guido]

I give up! I went to Canadian Tire and Home Depot and neither knew what a range vent is. They kept pointing ot the $2.99 plastic vents.
I decided to stick to the regular plasic flapper type. I realized my parents used this for 22 years without cleaning and without any problems at all.
If I notice abnormal grease buildup in the next couple years then I'll just swap the range hood for a non-vented hood.

Also - I searched the net for 1/2 hour and couldn't find a single one. I must not be searching by the proper term, but then again if they were common I should have found something. They don't seem popular at all, which makes me think that besides the code, they're not really necessary.

[Wgoodrich]

May be the wording you are looking for naming it by the wrong name. Try searching again for RANGE HOOD CAP OUTLETS.

I hit a search engine and found the above links with the below pictures in about 5 minutes. Just using the right terms makes all the difference. Try printing those pictures and take back to your supplier and ask for a product matching those pictures. Should help a lot. These range hood outlets are usually 7 or 8" round or rectangular. You may buy diverters to change from rectangluar to round if you need to.

Good Luck

Wg

http://www.selfhelpandmore.com/storage/forumanswers/rangehoodcaps.jpg