The advantage of multiple returns?
mwgaines
| Posted in Energy, Heating & Insulation on
Over the course of my life I’ve lived in two houses that had package heat pumps and one house that had a split system heat pump. All systems were total electric and had only one central return. I never recall any signifance problems with any of these systems providing adequate heating and cooling throughout the house. The cost of operation wasn’t excessive either. So what’s the real advantage of utilizing multiple returns with a forced air system? Is it just a measure to improve the rate of exchange to enhance the air quality?
Bumfuzzled,
Michael
New knowledge is priceless.
Used knowledge is even more valuable.
Replies
Comfort. It is hard to put air into a room unless you take it out.
Just to add a little to what rich1 said.
Comfort, meaning more even heat/cool distribution. You don't notice the variations in single story and smaller homes with a single returns, but in the larger the homes and two story homes there are often hot or cool areas because of poor air circulation with a single central return air. There have been several threads here, where people have complained about rooms on the second floor being hard to keep comfortable. Almost all of them had a single return in a hallway upstairs or even just one on the first floor.
Ideally you want about the same cfm of air entering and leaving each room or area of conditioned space. The cfm supplied to each space should be based on the load calculations for the space. If those calcs. indicate xx cfm for bedroom A, the supply duct size and return should be sized for that cfm, while bedroom B might require xxx cfm for supply and return. Having a central return in a hallway does not mean that the proper cfm of return air will be drawn from each room. The room futher away may be cold or hot, depending on the season, because of inadequate air exchanges, that can not satisfy the calculated load(s) for that space.
As houses get built tighter and larger, the problems with central returns beomes more pronounced.
Dave
Dave
Thanks, Dave. Very helpful explanation.
MichaelNew knowledge is priceless.
Used knowledge is even more valuable.
In a related area, I have a 30's house that I think had an original octopus heating system, as it has no air returns upstairs, but four monstrous floor returns on the first level. No complaints, but is it necessary with forced air now to have all of those big returns? I've considered reducing their size to regain floor space, but I don't wish to strangle the system. Any thoughts?
I'm not a HVAC expert, but I know comfort aside, you need adequate return for a Hight efficency furnace to even run. If you suffocate the furnace, the heat exchanger will get too hot, and the limit switch will cut out. I know from experience.
Another reason for a return in every room (except bathrooms) is to ensure that the air in any living space doesn't remain static. Where there is moisture and static air, their is a greater risk of molds. In our house, not only is there a return in every room and a cycling switch that runs the air handler twice a day, I also put UV lites in the return at the furnace.
Bruce