Air return placement

"gravity furnaces" work by convection. Warm air enters the room at a "warm "wall and rizes to the ceiling where it cools and falls down the "cole" wall. Putting heat up the cold wall causes the air to cool and drop without circulating. Most "octopus" or "gravity" furnaces discharged heat close to the center of the house with the cold air returns nearthe floor in outside walls or in the floor near the outside walls - often under winfows causing the still warm-ish air to cause a "curtain effect" at the window, drawing the cold draft into the cold air return. This is why when gravity furnaces were replaced with forced air units the total ducting had to be re-done - with some installers simply reversing the air flow - making the returns the heat outlets and the outlets the returns.

My brother's house in Kitchener is solid double brick with lathe and plaster interior - no stufs on the outer walls - and only about half an inch to an inch of "dead air space" as insulation. He has injected foam into most of the walls - not a complete fillbut enough to reduce convectgion loss in the airspace - which HAS helped a LOT.

Many of those buildings had "block fill" insulation inthe block cavities (often vermiculite) - otherwize the "dead air" in the cavities acted as a low value insulation. If fly-ash was used as the aggregate for the block(cinder block) the thermal conductivity of the blockis a lot lower than if granular stone was used.

I get that the ducting "should" be re-done. But millions of houses were converted from gravity to forced-air without the ducting actually changing.

Cindy Hamilton

Probably fly ash for my walls (the blocks are gray/black). Stone for the foundation blocks, which are the normal gray.

Cindy Hamilton

Without at lerast reversing the air flow the house will be hell to heart and NEVER be comfortable due to cold drafts.

Hell to heat? Not so much. Cold drafts, definitely.

My anecdotal "data" includes my grandparents' house, my mother's house, and the three houses that I've owned. All of them had the returns on the outside walls. All of them were built before 1960.

Cindy Hamilton