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.

In the past it hasn't been uncommon to use wall cavities as return air paths. However, it's best when the cavity is lined with sheetmetal. Having a return air cavity open to underneath the foundation and to bare earth is just not a good idea any way it's done. I sure would not want to be breathing in that air, and certainly would not want to know the effect it has on the furnace (potential dirt inside?). The best way, in my opinion, is to run the return ducts directly to the furnace, and have a plenum "box" built underneath the furnace that the return ducts lead to (or a trunk line of some sorts). This way you're not picking up excess outdoor air from underneath the foundation like you describe. Now is a good time to see if your furnace has adequate return air throughout the home (right now, since it's just bringing in air from underneath the house, I'm sure it has plenty).

What the tech has suggested might work if you had a low fan speed setting on your furnace. If the air flow is too fast then you may get a wind chill effect and you may actually feel colder. I doubt adding a second higher vent is going to make much a difference unless you had a cathedral ceiling. Try an experiment before cutting another vent. You may not like having the fan running for long periods of time.

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.