Hi I am new here, and my wife and I recently purchased our first home. Shortly after moving into our new home we had a high efficiency furnace put in and a new a/c unit. The furnace and the hot water are both natural gas appliances everything else is electric. Now when Manitoba Hydro came and inspected the furnace install we were told that we had downdraft being created when we used the dryer. Basically the dryer was grabbing air from the hot water tank exhaust pipe. So hydro basically told us that the house is air tight and that this downdraft is occurring because the dryer has no other place to grab air from. They gave us two options: 1. Switch to an electric hot water tank (we do not want to do this as this would double the energy needed to heat the water) 2. Bring in outside air via a fresh air vent. Now my father-in-law and myself put in the fresh air vent by sealing up one of the basement windows with two pieces of plywood, insulation and vapour barrier between them, and sealed up where the duct work comes through as well as sealed up the crack between the plywood and the window sill. What we are trying to figure out is how to minimize the air coming in. Basically we want to make it so no air comes in unless the dryer is on. Now we get a lot of condensation on our windows on the main floor during the winter months but I think that is a different conversation. I have read about ERV and HRV systems but to be honest it all just confused the hell out of me. I am a web developer and I am not afraid to admit that I do not understand this stuff at all. Basically we are want to know the most efficient way to utilize this fresh air vent (6" duct work) and to ensure that we are not increasing our heating costs during the winter and the cooling costs during the summer months. I hope this made sense if you have any questions please ask away.

You could bring the intake close to the dryer and close it with a damper when the dryer is off. Or a similar thing that is electrically operated from the dryer power. But sounds like you need a HRV or ERV.

yeah, according to manitoba hydro it has to be always open so can't put a dampener on it, I have been looking into a Direct Vent or Power Vent hot water tank that way it is a closed exhaust/intake system so then the dryer can't create the down draft.

wish I had the patience to read through all the different factors, but guess we need to get an audit done on the house to see how air tight it actually is, just not sure who around here does that sort of thing.

this is a very common problem. You should contact a professional. There is a health and safety risk if not addressed correctly.

If the place is tight enough that you're getting copious window condensation on better-grade double-panes you NEED an HRV, independent of the backdrafting issue, and the HRV/ERV itself might have sufficient cross sectional area to provide combustion air to a tank-type hot water heater.

If it's a "high efficiency" condensing furnace it usually means that it's power-vented (usually out the side) with rather than using the chimney, in which case you need to change to a power-vented water heater instead or the water heater's exhaust will condense and rot out the chimney from the interior anyway. Any power-vented water heater will do, but a condensing water heating tank would be more efficient and provide more hot water than most cheapie standalone tanks.

Using "sealed combustion" furnaces/boilers/water-heaters goes one better, since they don't use room air as combustion air and simply can't back-draft into the house no matter how many exhaust fans or dryers you have going.

Consider adding a 90-degree elbow pointing downward on the outside of the window and connected to the entrance to the ductwork that you added.  This will keep wind from directly blowing into the ductwork, and also reduce rain entering the ductwork.  This solution is not as good as a power damper, but it sounds like that is not allowed.

Install the power vent water heater. Consider any other gas appliances you may have in the house as well. Get an energy audit to determine your leakage rates and then you can get options for providing fresh air if needed. You need more data to do it right, but get the power vent.

Appart from the condensate issues and the fact that you need to do something about fresh air, the simples solution is to put an intake air pot on the end of the pipe. Any of the heating wholesalers should have them. Basically what the are is a pot somewhat larger in diameter then the intake. The outside of the pot rises higher than the bottom of the in pipe trapping cold air at the bottom. The cold air acts as a plug until the is a negative pressure in the house and then the fresh air spills over into the house

If you do not want to change any equipment then the proper amount of combustion air must be calculated.One 6" pipe does not comply to any mechanical codes.After the combustion air has been resolved then you could add a power vent to your existing water heater.

Posted By acwizard on 17 Oct 2012 01:46 AM
.After the combustion air has been resolved then you could add a power vent to your existing water heater.

Are you sure you can add a power vent? I didn't think you could do that. <> Anyways if you switch to a power vent WH, generally you dont need to worry about a fresh air intake unless your house is very tight. When the dryer is on it will use the next easiest pathway which is currently your b-vent.

Yeah we have the issue temporarily resolved with the 6" fresh air vent, we created a trap by using some insulated flex pipe and creating a giant u shape with it ending higher than the intake part. We have decided to save for a tankless system as it is looking like it will be the same price as going to a power vented or a direct vent hot water tank.

"Are you sure you can add a power vent?"
No you would have to replace water heater

"One 6" pipe does not comply to any mechanical codes"
There is a provision in the mechanical code for 1 pipe combustion air. Diameter depends on demand.

"You should contact a professional. There is a health and safety risk if not addressed correctly."
Bingo. The condensate on the windows is likely from the moisture in exhaust which contains CO among other things.
Make up air, HRV or combustion air- whatever quit talking about it and get somethin' done before the canary dies.

Manitoba Hydro has signed off that there is no risk anymore with the 6" fresh air vent. So now it is just a matter of saving up for the tankless hot water system.

I think you are missing a second point that there is such a thing as too tight.

At least you probably aren't adding HW tank exhaust to the list of indoor air pollutants.

I'm surprised that there isn't an active pressure balancer. Basically, fans to keep pressure generally neutral, perhaps slightly positive in the summer and slightly negative in the winter (both better for wall moisture issues).