[PRELUDE]

Hi folks
I would appreciated if any one of you with more knowledge on this subject could give me the better idea that answer would be yes or no.
With the exception of kitchen and bathroom, Do we need cold air return to furnace in every room?
What would be the major problem by not having one for each bedroom but two large one in living room?
I must add this to the question that this is for 3 bedroom house with no AC just heating and about 1000 square feet.

Thanks    

[mcgsxr]

Not sure, but in my house (17 years old now), not all rooms have a cold air return upstairs.  One in the main hallway, one per bedroom but one does. to have one. Main floor (open plan) there are only 2 in the whole 1000 square feet. 

In my basement I elected to not put one in, based on research.  There were differing opinions, but no concensus, and knowing I could put one in later if I had to, I left it out for noise concerns. 

[Ericus Rex]

All the houses I've ever lived in with forced-air heating had only one return in a central location...all single story houses, btw.

[PRELUDE]

Not sure, but in my house (17 years old now), not all rooms have a cold air return upstairs.  One in the main hallway, one per bedroom but one does. to have one. Main floor (open plan) there are only 2 in the whole 1000 square feet. 

In my basement I elected to not put one in, based on research.  There were differing opinions, but no concensus, and knowing I could put one in later if I had to, I left it out for noise concerns.

I did some search about the basement and came up to the same idea that I do not want one.

[PRELUDE]

All the houses I've ever lived in with forced-air heating had only one return in a central location...all single story houses, btw.

That is good to know, thanks.

[Big Red Machine]

All the houses I have owned (7) have had cold air returns in every room both upstairs, main, and basement.  Otherwise how do you exchange the newly heated air with the cooled air?

[mcgsxr]

I cannot provide any science based answer to why the returns are where they are, but having recently had both furnace and AC replaced, the techs looked around at the existing lines, and said all was well.  I explained I was not going to install a cold air return in the basement, they were not concerned.  The existing basement lines were simply extended or shortened.

The addition of a cold air return (I feared) could lead to more sound leakage out of the basement. 

[Martyn]

I believe that the answer to your original question is no, you don't need a cold air return in every room. That said, you should always check your local codes.

Here's my logic: the supply side of your hot air is distributed throughout the house under pressure which is produced by the furnace's fan, and the branches of the ductwork are sized such that they deliver the right air flow rate to each room (with a little help from the diffusers or registers). The return side, on the other hand, is not pressurized, except perhaps by a small positive pressure in each room. So is is important to minimize the "resistance" or pressure-drop in the return ducting, or the fan won't be able to draw any return air. It's rather like trying to suck a candle out through a straw. Thus it's common to have large return registers feeding large, short runs of ducting back to the fan so as to minimize pressure drops. If you take this to extremes and have, say, only one return register, you risk creating a short-circuit that returns more air from the nearest diffusers and less from the rooms that are further away. Interior doors are usually undercut by about an inch to provide a gap between the bottom of the doors and the finished floors so that air can move around unimpeded.

If you are designing your own forced-air ducting arrangement, you should get qualified help unless you are very experienced yourself. It's not as easy as it looks!

Martyn

[Scott F.]

Here are a couple of things you need to consider.

You can get by with just a few well placed return air ducts providing you do a couple things. Each room with a door needs to have that door undercut by a fair amount to allow enough return air to flow from the space. There is a caveat to that concept. Not to get to technical but this is what I do for a living (HVAC engineering), the undercut on the door needs sized so that you don't create more than (say) 3/4"-1" of static pressure across the surface area.

If the undercut creates too much static, the air won't exchange in that room and you won't be able to maintain setpoint in that room. I'm not sure what kind of static pressure your furnace can handle but typically a residential unit won't do more than about 1"-1 1/2". I've got a new Carrier with the ECM motor. It can handle just about 2".

Basically, to maintain a reasonable temperature gradient across your house you have to either install return air ducts, undercut the doors OR leave the doors open to each room. Myself, I'd go for the returns in each room.

[jea48]

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[JLM]

Echo Scott.

Most air in forced air systems is recirculated.  The old-school classic residential design uses an octopus supply system (ducts radiate from a central furnace to diffusers on the building perimeter) and a single central return.  To provide more even tempering, air must be returned from at least each level of the home (as alluded to above in order for the the supply ventilation to enter the space it must displace air that's already in the room).  Note that the air pressures (static) involved in typical residential designs are quite small (positive - pushing on the supply ducts and negative - sucking on the return ducts).  Pressures in the rooms themselves are tiny.  The ventilation related disadvantage of door undercuts is in the flooring (if not properly accounted for or replaced later with something thicker) the clear opening would be reduced and along with it return ventilation.  From a fire standpoint, there is maximum undercuts so that doors contain smoke.

No return in the basement results in cold basements in cold climates.  Warm air rises, cold air sinks, so a basement is where cold air tends to collect.  Typical basement supply diffusers are shooting down from the ceiling, so no way to get warmth to the basement floor.  A good solution is to cut a grille into the return air trunk (near the floor) just before it reaches the furnace.  This grille can be in the furnace/utility room to minimize noise to the rest of the basement (if you have sufficient undercut on the door to that room assuming it's in a room).

[PRELUDE]

Thanks to all the folks who is answering the question.
Here is the plan. I have two returns in the living room one is at the corner and the other one is in the center which is almost located at the center of the house  as well. The size of each is 30"x 8". The living room size is 25'x12'x8'.
Now what I try to do is to eliminate the returns in the bed rooms to reduce some duct work in the basement to gain some height as well better sound proofing because half the basement will be finished soon. The furnace is old now but I am buying the new one next week and it will be 96% efficient with two pvc pipe goes out side the house.
But I want to make sure to do not create any problem in the future by eliminating those returns.

[ctviggen]

Interesting thread.  Our house does not have a cold air return in the basement.  We have two main zones, one for the first floor and one for the second floor.  The runs for the first floor are in the basement and the runs for the second floor are in the attic.  The basement is not heated or cooled.  We have intakes and returns in each room. 

[Charles Xavier]

Where is the P-Man when you need him ?




 I believe he does this for a living. Give him a shout.

[Martyn]

It might be too late for this if you have already ordered your new furnace, but have you considered alternative heat sources? I tore out my inefficient 25 year old oil-fired furnace together with all the ducting and replaced it with electric radiant heating. This eliminated all the noise, dust, and drafts associated with forced air and allowed me to turn my basement into useful full-height finished living space. Not a small project though, and might not work if you need A/C or dehumidification...

[PRELUDE]

It might be too late for this if you have already ordered your new furnace, but have you considered alternative heat sources? I tore out my inefficient 25 year old oil-fired furnace together with all the ducting and replaced it with electric radiant heating. This eliminated all the noise, dust, and drafts associated with forced air and allowed me to turn my basement into useful full-height finished living space. Not a small project though, and might not work if you need A/C or dehumidification...

Thanks, but electric would not work for me because of my main panel is full + the sub panel for work shop.

[MtnHam]

Electric is generally the most expensive way to heat! The layout of the house will determine where and how many return air ducts are needed. My current home has one return duct- in the door of the furnace room itself! IMHO, a return in every room is overkill.

[ctviggen]

Electric is generally the most expensive way to heat! The layout of the house will determine where and how many return air ducts are needed. My current home has one return duct- in the door of the furnace room itself! IMHO, a return in every room is overkill.

I think you should've stopped at "needed".  My house is 4,100 square feet (includes an in law apartment that's at least 700 square feet, and we've also given her another room; she probably has close to 1,000 square feet).   It's two floors, too.  How could all this space only have one return? 

[Martyn]

Electric is generally the most expensive way to heat!

This is true...if you live in an area where electricity is expensive and heating oil is cheap. Where I live, my annual electricity bill now (for heating, cooking, lighting, and hot water) is about the same as my fuel oil bill was seven years ago (just for heating). Radiant heating on programmable thermostats is very efficient, as well as being very comfortable and absolutely silent.

[JLM]

Electric heat can be relatively efficient (no fan energy needed) and if you only live in part of the house in the winter due to the option to zone or even go with a portable electric heater (forced air systems that can zone are fairly expensive), but without ducts there is no way to provide central humidification or air conditioning (but can be better for allergy sufferers).  Venting odors can be another problem as infiltration is the only way to replace exhausted air and doesn't address general odors (cooking, dogs, etc.).  But the most efficient electric heat is combination infrared (that heat only objects in the room)/convention (designed to incidentally heat the air) units.  Ceramic/mica based portable heaters are relatively safe, inexpensive, no fans, and quite efficient.

Again, with the very low pressurizations involved you can start to think of a room like a balloon.  Until you let some air out (return/exhaust ventilation or open door) it's hard to push more air in (supply ventilation).  And unless you direct where the air moves from/to it will always pick the path of least resistance (larger openings, shorter paths, fewer turns), explaining why the most remote rooms are doubly hard to heat/cool.  Our 8 year old 2 story with finished basement EPA 5 star house has one return on each level.