I have an old (1916) 2 story house with gas furnace located in a basement utility room. I have no cold air returns on the second floor. I have 3 cold air returns in the main floor (living room, entrance hall and dining room). Only the return in the living room is connected to the furnace air intake through ductwork. The return in the dining room is sealed and the return in the entrance hall is open to the space between the floor joists and the sheet rock ceiling in the basement. The return duct from the living room connects to the furnace air intake and the furnace air intake is also connected to a grill in the utility room wall and pulls cold air from the basement. The basement is finished but it has a hole in the wall sheetrock (exterior wall) to provide access to a sewer cleanout. As a result, the furnace draws primarily cold air from the basement and wall cavity and only a portion of conditioned living space air. This reduces the efficency of my furnace. I am in process of sealing my basement and using it as an entertainment room. Do I need to redo the ductwork to connect up the 2 air returns?. This may be difficult due to the direction of the floor joists and low ceilings. One possibility I am thinking about is to seal the basement space and connect the 2 returns to the basement by installing flexible ducts from the floor returns to grills in the basement ceiling so that the basement serves as part of the conditioned space thus eliminating the need for return air ducts in the basement. Does anyone have any thoughts on this approach? Will it result is noise or some other performance problem.

You'll hear a lot of debate about this one - some will say you can't do it without calculating a Manual J etc but the reality is there's a lot of boilerplate hvac systems, at least where I am in Canada. I have two returns in the upper floor of my house only a couple of metres apart, and none in the finished basement and none in any of the bedrooms, which I've been told is an 'impossibility' - well here in Canada, it's not and the system works well enough - the master bedroom is a bit cooler with the door closed, but it's above a poorly insulated garage. I see a lot of basements with the return in the ceiling. Warm air does rise, though, and in the summer you might want some of that cooler air in the basement circulating upstairs, so I'm planning to do exactly what you mentioned, put the return near the floor, backing onto the furnace room. If there was some sort of big issue with changed airflow, you could probably block off an equivalent of the downstairs return vent in the upper return, to equalise the air flow, but to this layperson, the SUPPLY of cold air is not as much of an issue if you're not getting cavitation (a vacuum effect because the pump isn't able to suck in as much air as it's trying to deliver.) Take some temperature readings over a few hours in different spots in the house, and make note whether the furnace is running a lot more than it was previously. The 'duct work' typically is either the space between floor joists or a boxed duct around the same size, or, running down the wall, typical stud wall spacing, 16." That's what I see here in British Columbia, again, I'm not an HVAC tech. Don't go excessively large. If you go through the furnace room wall you won't need much in the way of ducting and if you need to you can use thermopan (silver faced cardboard) instead of drywall or OSB to form the 'duct' from the floor up to the return (make sure you cut into the return, not the warm air section and make triple sure you're not going to damage any wires, gas lines, a/c lines etc. As for the return, the standard size grille is about the width of the space between studs I guess so around 16?" If you need to tweak it, you can block sections of it or the upstairs one inside under the grille if you need to. If you're careful, you're not going to damage anything irrevocably.

It would appear that somehow your fireplace insert is tied in with you regular heating system. You will have to go do a little crawling around and tracing of the duct work and block it off where it needs to be. You have to be careful though to make sure it doesn't affect the rest of your system. If you're not comfortable doing it or not sure you're probably better off hiring someone who will understand what they're looking at in your house. It's pretty difficult to see into your basement from here.

" It is a very hard design to heat or cool evenly." That is undouptedly true and all the more reason not to mess around with diy, roll your own and home made desighn changes to hvac system. On the surface your idea sound's like there is a free lunch to be had pulling cool air from basement. It's far more complicated than sticking a return in the basement. For every cubic foot of air sucked from basement,another cubic foot must replace it. That make up air can only come from outdoors (a terrible idea) or withing the building(which is exactly how every room in building is usually desighned). Trade schools spend hours teaching techs this so just believe me when I tell you for every cubic foot of air "falling down stairs"another cubic foot already "falls right back up them". So if you want to heat and cool basement,you should have ducts in it. If you don't care to have basement heated and cooled,make certain there are no leaks in existing ducts ( both supply and return ). Now so you don't go away empty handed,a simple test that might tell you if theres a leak in supply or return in basement. Hang a bed sheet,thin plastic or similar light fabric to cover doorway leading to basement. If sheet moves toward basement there's a leak in return. If sheet moves away from basement there's a leak in supply. If sheet doesn't move at all the bad news is there's a "REMOTE" chance leaks of exact same size exist's in both supply and return. I'm assuming your air handeler is in basement or main trunks run through it,if not,little I've said is applicial for your house.