I'm an electrician living in Manitoba, Canada, where the winters get COLD!  The house we're building is 1550sq ft bungalow, full basement. have 2x6 walls, 1 inch foam, triple pane Huron windows, ICF basement, etc.  We're using electric forced heat, the best thing in this part of the country.  My one concern is the ducting layout.  The way they've been doing it for years has been ducts under every window, and the returns in the center of the house.  My father in law brought to my attention the old way of doing it.  Furnace ducts more in the middle of the house, right off the main, and the returns by the window.  His theory is that your blowing the air from the center of an area (our house is very open)  blowing it towards the outsides, and then the returns pull it in towards the windows, not allowing them to fog up.  The advantage here is that you heat up your living space better, and there's more force coming out of the ductwork.  My concern is the windows: will they fog up?  I will have ceiling fans, i'm a firm believer in them, and with the 6 inch cold air intake, the air will be very dry coming in. This is my first post, and I thank you in advance for any feedback.

Jason

I may be stating the obvious, but the supply duct also prevents condensation on your windows in a cold climate.

We just figured that with an air tight house and ceiling fans, the air would move around, from center to the outside walls, but we may be wrong...

Duct location has very little effect on window condensation issues ( but it can effect comfort somewhat.) The moisture content of both the supply and return air is the same, only the temperature is different. It's the temperature of the window relative to the humidity (not the temperature) of the room air that makes the difference as to whether there is condensation or not. Placing the supply duct under the window doesn't appreciably raise the temperature of the window except during active blowing cycles. The average temp of the window will be about the same (as will the amount of condensation.)

But triple-pane windows will have far less condensation than old-school goods.

The total impedance of the ducts is unaffected by which are the supplies and which are the returns- it doesn't "...heat up the space better..." by having "...more force coming out of the ductwork...". The total air flow is determined by the combined supply and return impedance. If the duct system is designed in compliance with ACCA Manual-D standards, and mastic-seal the joints & seams it will provide satisfactory results whether the registers by the windows are supplies OR returns. Insulating at the supply ducts to at least R6 (if they run in conditioned space- more if any part of it is in unconditioned space), will result in more consistent balance and higher system efficiency (by delivering more of the heat where it was designed to go rather than dissipating into adjacent space along it's path.)

So I guess it doesn't really matter then, just as along we have a balanced intake\supply where we get the most out of the furnaces air flow. By blowing air onto the cool windows, does the supply air cool down quicker? Thanks for all the replies!

dont put the returns by the windows... If it aint broke, dont fix it hahaha

in cold climates supply registers spilling on the windows do help as the warm air is able to absorb excess moisture from surface of window pane and provide more consistent temp across conditioned space...Eric

My concern would be one of comfort. With no air circulation (in either concept), air cooled by the windows will fall to the floor. When the furnace is running with the supply under the windows, the supply air will counter the drafts.

With the supply running across the ceiling and down the window, the supply air temp will be at or close to ambient room temp by the time it gets to the window and will be further cooled by the window. I am afraid that the effect if the downward flowing air will create a "power assist" to the natural convection and create a draft along the floor.

In your favor are ICF and good windows. The interior wall temp should be at or very near to the room temp so walls should not contribute to a potential draft problem.

Again, I would worry more about comfort (as Dana1 mentioned in his response) than condensation.

Bruce

By the way, both women and men can be named Dana.  I know everyone wants to think that Dana1 is male but there is a chance that she is female.  If so, then we should be saying her instead of his.  Maybe Dana1 will set us straight so we will know which pronoun to use.

Posted By Alton on 02 Jul 2010 06:30 PM
By the way, both women and men can be named Dana.  I know everyone wants to think that Dana1 is male but there is a chance that she is female.  If so, then we should be saying her instead of his.  Maybe Dana1 will set us straight so we will know which pronoun to use.

Last time I checked (which was earlier today) I was still of the masculine gender, but I s'pose you can never be too sure- a dna test might be in order, mayhaps!?!

Thanks Dana1,

From your writings I truly had no idea.  I was just pointing out to everyone not to assume they know someone's gender.  I also want to thank you for the tremendous contribution you have made and contiune to make to Green Building Talk.

Well it looks serious problem, if the construction structure is well defined i think there is no need to take tension, just call a service provider he will have the solution of your problem. :D