Hello - I currently reside in Rochester, NY. I have a cold air return duct running up through the center of the house from the furnace up to the attic. Its blocked off at the attic. I want to heat the attic and want to run some sort of smaller diameter, flexible hot air supply pipe up through the cold air return from the furnace up to the attic.

Questions:

1. Is this "OK" from an HVAC mechanics perspective to do this?

2. Is this a problem with any code?

3. Are there any other issues I should consider?

Thanks in advance for any input.

What does the return do now? And what size is it?

10" x 3.25"

Currently acting as one of three cold air returns in a 1900 square foot house built in 1930. It is the sole cold air return for the upstairs (3 beds, one bath). Pulls air from 2 of the three bedrooms through a shared wall grate.

Do you have ac? If not, should be fine to use it.

Yes we do have ac. What problem would this create?

Well first off you do not want to put the ac into the attic, just a waist of cold air. So you will need some sort of damper to close the pipe in the summer. Other then that not much as I figure with only that small of a return it is probably a good bit warmer upstairs in the summer then the main floor.

Yes, it is a bit warmer upstairs - but in our climate, we really don't use the A/C all that much.

Good point on the damper. I'll do that. Thanks for your input.