If the funace cycles half as long... is it cycling twice as often?
Unless you've altered the heat loss properties of the structure, you will still need the same BTU's to heat it. The savings would be from distributing heat more evenly allowing a lower setpoint to be used and reducing temperature swings.
I read several papers thsi morning regarding duct design and all menton that while it's optimum ot have a high return for cooling and low return for heating, ultimately return placement has a relatively small impact. As the pro's on this board have said, it's the velocity and mixing affect of the supplies that heat the home along with in large part conduction. A return won't pull air down from the ceiling or draw air from across the floor. A supply however CAN do this.
and you feel the room temp is being raised in half the time due to pulling down the hot air from the ceiling instead of it eventually mixing on its own?
Let me clarify further. Warmer air near the ceiling is not “pulled down”, it naturally descends do to the floor because the colder floor air is being removed. Inversely, if the warmer air near the ceiling is being removed the opposite will occur. As the warmer air is removed, the colder floor air will naturally rise or occupy more space.
Trying to mix all the air to eliminate stratification is a pipe dream. Lowering a return to get the most out of your heater is step one, trying to mix air is the band-aid for improper ductwork.
The reason the Pro defends ceiling returns is because:
They are easy to install.
They are unwilling or unable to explain the benefits of floor returns on heaters.
They do not want to do the extra work for limited compensation.
Their competition is not bidding for that work, so they won’t.
The architect and GC regularly do not demand it.
They may not know what a dual duct system is.
They are trying to keep the price down.
But rather than face these realities, it is easier to just point to a ‘Manual’ or a magic supply register.
Like I said before, I’d love to take the money from any Pro who would bet me.