Sorry forgot to add the product url:

Here is a link that might be useful: Dundas Jafine draft blocker

Fiberglass doesn't work well to stop drafts so you are right in sealing that opening with foam. Air is very lazy. It doesn't like rough surfaces or sharp corners or pushing things out of the way. Metal vent ducting is smoother and air will move through it much more effectively than the vinyl stuff. But long runs make it more difficult for the air to move through the clothes and out of the dryer, and if you add another backdraft damper, the air flow will be further impeded - even if it is "light". The Dundas units are pretty good. Also check out www.heartlandnatural.com/Household/dryervent/index.htm. But if you are considering doing it, you might want to add a booster fan to make sure the air moves all the way through. Check out the booster fans at:

Here is a link that might be useful: Heyoka Solutions

Something I did here in Florida...probably not as practical in colder climates...I have a second vent pipe run down from my attic terminating with a grill behind my dryer. The idea is to close the laundry room door when the dryer is in operation, allowing the replacement air for the venting dryer to be pulled from the attic (already warm air) rather than pulling hot air into the whole house through the cracks around the windows and doors. Kind of like outside air intake on fireplace.

I wondered about flow impedence, I can't remember what the rules are here for distance of run but the flow seems pretty decent and when I get the whole thing cleaned, it'll be better, I don't think the damper will impede it *too* much but a booster may be something to think about, but on the downside, more power consumption, and also more negative pressure, I think eventually I'll need some sort of supplementary air intake to the house to avoid sucking back products of combustion from furnace/HWH, especially if we get a gas cooktop and vent our range hood outside, currently it's just recirculating and fairly useless. Our smoke detector goes off frequently when we're cooking.

My furnace has the air intake that runs from outside to the cold air return (I'm in BC Canada btw) and combustion air is drawn from surrounds via louvred doors, if more "make up" air is required, how is it usually supplied? I don't imaging a heat recovery/fresh air exchanger does this job as I assume it intake/exhausts equal amounts of air?

I love the idea of drawing the warm air from the attic (provided it's not humid) in some climates provided you're not sucking up fibreglass dust from the insulation; in my old house when I lived in Australia this would have worked well, having said that, there is no code to enforce dryers being vented outside, I chose to do so with mine and had to look hard for a ventable model (no gas dryers there, everything's 240v anyway) - and this in a country with usually very high humidity. Not sure what's up with that. In winter, the heat's good but we could certainly have done without any extra humidity

I bought dfaft blocker from home depot in canada alberta, my flex pipe and dryer over heated, the temperature here is -15 with the wind jan 02,, 2016 it seems it only applicable to summer temperature...

larrypo, the dryer and pipe would only overheat if there is not enough flow of air. i.e. it is too restricted. Even in winter, you would still have the air restriction problem not being able to keep up with your dryer, making it less efficient and having to run longer and harder to get the clothes dry. And burning out your dryer resulting in needing to replace them more often. And it is a fire hazard. If the flow of air is not strong enough dryer lint will stick to the inside of the pipe.