Air conditioning a no-return house
Looking for some suggestions on air-conditioning my house. It’s a forced air system with plenty of ducts to keep the house warm in the winter. It has no return vents except for vents that drop the cold air from the 1st floor to the basement, where the furnace picks it up. Low basement ceilings (6feet and change) and existing ductwork would make it hard to setup a fully-ducted return system which already doesn’t seem to be necessary for the heating season. There is a fresh-air opening to the outside which is always open.
My question is, I figure I have two options. One is to make warm-air returns on the 1st and 2nd floor to the basement, but not all the way back to the furnace. A low center beam in the basement would make it diffcult to cross from one side of the basement to the other with a duct. The open floor plan on the 1st floor would make it hard to find a common wall on the 1st and 2nd floor to drop straight down. The way the heating system works now, I figure it won’t be a big deal anyway. My only concern is would the furnace be able to pull the hot air into the registers since hot air wants to rise. A lack of a vacuum in the basement might make this hard. I could find a way to close off the existing returns in the floor.
So… My other idea is to add a whole-house vent fan in the hallway of the 2nd floor to pull hot air from the first floor up the steps (?) and from the 3 bedrooms assuming I make some vents over the doors to allow hot air to escape. The vent would be in an ideal position at the top of steps, and in the attic would be right below a window fan the previous owner used in the summer. The hot air would be pulled into the attic and the window fan would move it outside, using a relay that would come on when the furnace blower was running. Seems pretty simple to me actually and more efficient than recycling air in an already leaky, 80+ year old house. I already have a ridge vent in the attic to hopefully keep hot air buildup to a minimum. Question here is, how much CFM do I need for an 1800 sq. ft. house, with a 9ft. first floor?
I know this probably isn’t a common setup, but the alternatives are a convulted basement duct system with no headroom and alot of mess opening up the plaster walls, a high-velocity system ($$) or another hot, humid summer…
Thanks,
PJ
Replies
Another option might be to install a separate system in the attic for the 2nd floor.
I have a few reasons why I don't like that idea, all the (new) ductwork that is required so I still have to open up a few walls, and still figure out some return system for the 1st floor; running the extra electric for the air handler and the refrigerant line up 2 floors; get rid of the condensed water; Attics get hot, wouldn't this reduce the efficiency of the system a bunch? I could insulate the handler and ducts to fix that some, but I figure if I'm opening up the walls to run ducts, might as well use the existing air handler. Also, the attic is used for much storage, and *might* be an extra room someday.
I guess my concern has to do with the efficiency of exhausting the hot air, instead of doing what proper systems do by recycling it using the return system. I know it's hard to answer, but am I looking at the possibility of wasting conditioned air that might get blown out the window? Take the 1st floor returns for example. Would it be better to return them to the basement or to the attic?
PJ
by the time you fool around with this abnoxious designed layout, you would be further ahead to start from scratch and install a conventional duct layout with proper Returns directly associated with the supplying appliance.(Unit)
One option would be to use the system as-is and see what happens. Obviuosly, this is not ideal, but seems to be working for hot air. So long as air flows through the coil at a rate to prevent freeze-up (> 320 cfm/ton) you will do no harm.
I have an old 2 story house (1850) which has hot water baseboard heat.
I added A/C to the 2nd floor only with all duct in the attic. Seems to work pretty well - the temperature differential between the 1st and 2nd floor is only about 3 degrees F. I have a center hall floorplan with a big open staircase so apparently plenty of cold air falls to the 1st floor.