Cold Air Return; how do these work?

[woodsie8]

I have one in the floor, and one in the wall, at the top of the stairs; which is almost directly above the floor one. People have told me that during the summer, you cover one and in the winter you cover the other one. The one at the ceiling in the stairwell, has dust and cobwebs on it, telling me that sucks inward.
Why do I have two, how are they usually connected to the ducts, and how will I use these once the insert is installed?

 

[begreen]

I have one in the floor, and one in the wall, at the top of the stairs; which is almost directly above the floor one. People have told me that during the summer, you cover one and in the winter you cover the other one. The one at the ceiling in the stairwell, has dust and cobwebs on it, telling me that sucks inward.
Why do I have two, how are they usually connected to the ducts, and how will I use these once the insert is installed?

Is this a heating only system or heat and cool?

The two returns are tied together into a common plenum at the furnace. Normally it's not a good idea to block off a return grille. The system should be balanced to put a specific load on the fan motor and deliver a specific output through the supply ducts.

Normally you won't be using the HVAC system at all while the insert is running. Redistributing the heat via the HVAC system is often inefficient due to heat losses in the ductwork and increase electricity usage. However, if all of the ductwork is within the heated house envelope and very well insulated, the fan on the HVAC system may help to even out house temps if it is run for a little bit every hour while the wood stove is burning. YMMV.

 

[woodsie8]

No A/C. Oil burning furnace that is on the outside of the house, duct under house, then vents in each room. Two story house. The stove guy said one pulled in and one pulled out, that is why you use a different one for winter and one for summer. Does that make sense? I have a rug over the floor one, now. I actually saw on-line somewhere, magnetic covers to put on one of the vents, during the season you don't use it and then the move it to the other one, during the other season.

 

[begreen]

There are lots of gimmicks and half-baked ideas for heating system modifications. Almost all are bandaids for badly designed systems or misinformed individuals. Many are a bad idea.

If your system is heat only then it is idle in the summer, right? There is no need to do anything to the return grille during the summer. Are you certain the oil furnace is on the outside of the house? That isn't a common arrangement. It sounds inefficient.

As to the grilles, I think what is confusing is that many systems are heat/cool. Some of these systems have been intentionally designed with two returns. In this case, there is a low return for winter and a high return for summer and each has been designed to return the proper amount of air to the blower. One should only close off the opposing return grille on a seasonal basis if the system was designed to do this. But that is a hassle, and homeowners can be notoriously poor at maintenance, so more often the system is designed with two returns, one at a high point of the system and one at the low point. Both return grilles stay open year round. This is what your house sounds like.

Without actually seeing the ducts, knowing the grille and plenum sizing, I would only be guessing how it was designed. It may be set up for adding AC or it may be balanced using both return grilles. Before blocking off anything, best to get an expert eye on the system to help you understand its setup and proper operation. Until then, don't block off either return grille in the winter when the furnace is running.

 

[woodsie8]

It has a summer fan, but no A/C. The furnace is definately outside, in a closet attached to the outside wall of the house. They use to have it in the crawlspace under the house, but when they replaced the furnace, they put the new one outside. Probably because there isn't any place inside to put it.

 

[Carl]

Like BeGreen has stated, it is not wise to block off any return grilles for the furnace. These are ment to feed air to the heating system to balance out the air blowing out of the ductwork. If closed off it WILL reduce the efficency of your furnace or air conditioning system and WILL put undue wear on the blower causing it to overheat or wear out very quickly. If the furnace was just replaced as you stated they would have calculated the air needs of the unit and provided proper air requirements for it. With the furnace being located outside this return line is very important.