Gas Furnace Inflow Question

My gas furnace continues to work well, as it has for 25 years. The air intake to it is from an enclosed space below the furnace which in turn has a screened opening (12" x 18"?) into my living room about 1 foot off the floor. That space also has a small opening (4" x 6"?) to the outside of the house. Thus the cooler air from the living room, mixed with some air from the outside, is sucked into the furnace, heated, and sent out through the vent system.
I just had my home fumigated, and when the gas company technician was turning the gas back on, and lighting the furnace pilot, he suggested that I close off the small opening to the outside. He said it would prevent rodents from entering the house, and would decrease my gas bill by a small amount.
This small opening to the outside was purposefully placed there, along with a rain shield on the outside, by the builder of this group of tract houses. The home is on a concrete slab.
Any safety or other reasons NOT to close off this opening, as the gas company representative suggested? In case climate is relevant, I live in the greater Los Angeles area.
Thanks.
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CWLee
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There are several legal ways to vent a gas appliance. I suggest that you check with the local authorities about any changes your planning. Now days the Plumbing code requires 2 vents one high and one low. My water heater can draw air from the outside and the attic.
Personally I would not have the heater using inside air for combustion. It is legal and is the way it was done for a long time, when gas was cheap. For me it defeats the purpose of the heater. Moving all that air from inside the house then replacing it with cold air. Properly sized vents to the outside would allow you to pressurize your home (slightly) and keep the chances of Carbon monoxide in the furnace room. Not where you breathe.
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I may not have expressed myself clearly, or perhaps I don't understand what you mean by venting, but the situation I'm talking about is the air to be heated and circulated through the house. The issue is whether that incoming air should remain a mixture of inside and outside air, or whether it is better to use only inside air.
He also wrote:

Sorry, but I'm having trouble understanding what is meant here. I'm not talking about the air used for combustion, but the air to be heated and circulated through the house. The savings in dollars the gas company representative had in mind was from NOT heating up cold outside air but rather heating the inside air, which would be at a higher temp than the outside air, and thus require less gas to increase its temp to the desired level.
He also wrote:

I assume it is already properly vented, since it has passed several inspections by those familiar with local building codes. I futher assume that the gas company representative would not be suggesting something that would result in an improperly vented furnace. As I understand the concept of venting, it is a means to draw off the carbon monoxide and other undesireable fumes so they are expelled to the outside, and not circulated into the house. The gas comopany representative did a "venting test" and told me that the fumes were going just where they were supposed to go, up the vent and through the roof.
Pehaps you can clarify what you meant after reading my comments.
Thanks.
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Contact a licensed professional heating company and ask them. Anything more I say will probably be misunderstood and I can not see the installation.
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CWLee wrote:

(Snipped))
It is simple. Most or many older systems had no requirement and have no way to supply outside air into the system. With the construction of tighter houses, it has been recognized that inflow of outside air is required to provide a decent quality of air in a building. In our jurisdiction, new installation requires an outside air inflow to provide a 10 percent air replacement. All you need is a screened outside vent to tie into the cold air return just above the furnace filter. Other jurisdictions may require different percentages.
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Thank you. What you describe sounds exactly like what I have, in a house built in Los Angeles County 25 years ago. I had no reason to change that until the gas company technician, here for other purposes, suggested that I close off that outside air inflow to prevent rodents and to save a small amount of gas. It seems strange that, in his official duties, he would suggest something that may be against the building code. I continue to be puzzled about the idea.
Thanks again.
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Furnaces actually have two air flow circuits. One is the air which his heated (or cooled). The second air flow is combustion air. the burner needs air from some where, to burn and then the exhaust goes up the chimney. I suspect the smaller vent is for combustion air.
Screen it if you want (coarse screen) but I wouldn't close it. Unless I knew there was some other source of combustion air.
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Christopher A. Young
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Thank you, "Stormin Mormon" for your comment.
I'll try to present this situation in a different manner, since I think I'm confusing people with what I wrote before.
Living room air flows into a "space" adjacent to the furnace which is located on the other side of the wall in the garage. This air flow from the living room is through a grill about 12" x 18" into the "space" which is perhaps 6 cubic feet of space. Also feeding into this "space" is an opening to the outside, about 4" x 6". Above this "space" is the air filter that is below the furnace intake. I believe this is the air that the furnace heats and recirculates through the ductwork in the house. I don't know where the flame gets its air for combustion (perhaps from the air in the garage, which has loose doors to the outside as well as some vents in the walls), but there is a vent above the flame that goes up through the roof. Per the gas company technician this combustion vent is working just fine. He held a burning match there and watched the smoke go where he said it was supposed to go.
After checking the furnace, and before he replaced the furnace filter he pointed to the small (4" x 6") vent to the outside, and suggested I block it off to prevent rodents from entering, and to save a small amount of gas by not heating up cooler air from the outside, and just heating up warmer air from inside the house.
I'm still curious about any safety issues associated with closing that small opening to the outside, thus blocking off a purposefully built entryway for air. The house was built 25 years ago and passed the various code inspections at the time, and since then.
Thanks again.
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wrote:

The entire installation sounds like one big safety nightmare that wouldn't meet codes in any jurisdiction (seriously).
- Furnace in garage. - Return not ducted. - Only one combustion air vent. - Who knows what else?
I suggest you get the factory authorized dealer to inspect your furnace and situation and make any needed repairs to bring it up to code. Also, be sure to get your local building inspector to check it out afterwards.
Fix it unless you don't care about poisoning your family with deadly carbon monoxide and/or burning your house down.
I would shut the gas off to the unit and disconnect the power until you have it fixed. That thing is a killer.
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If you are serious, and not pulling my leg or being inappropriately alarmist, then I think I have not adequately explained the situation.
There must be 10s of thousands, if not 100s of thousands, of homes in Southern California which have their furnace in their garage. I don't think that is contrary to local building codes or manufacturer's recommendations.
"Return not ducted" may or may not be correct, based on what I understand, observe, and have written about the situation. The heated air from the furnace is in fact distributed through an extensive system of ductwork throughout the house. Is that the "return" you are talking about?
"Only one combustion air vent" again may or may not be correct, but the fact that the gas company technician, and the local building inspectors have all found nothing hazardous about the installation cause me to believe there is a second combustion air vent, or that such a second one is not necessary due to the location inside a garage.
Thank you for your comments.
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By return air not being ducted, I THINK he is referring to the fact tha you need your return air (the air being pulled from your house into th furnace) to be sealed off totally from the combustion air (air used fo combustion). You would accomplish this by ducting the return ai directly to the furnace, rather than just funneling it into this space which also contains combustion air. Not sure if that's what yours i doing or not...
___________
If you are serious, and not pulling my leg or being inappropriately alarmist, then I think I have not adequately explained the situation.
There must be 10s of thousands, if not 100s of thousands, of homes in Southern California which have their furnace in their garage. I don't think that is contrary to local building codes or manufacturer's recommendations.
"Return not ducted" may or may not be correct, based on what I understand, observe, and have written about the situation. The heated air from the furnace is in fact distributed through an extensive system of ductwork throughout the house. Is that the "return" you are talking about?
"Only one combustion air vent" again may or may not be correct, but the fact that the gas company technician, and the local building inspectors have all found nothing hazardous about the installation cause me to believe there is a second combustion air vent, or that such a second one is not necessary due to the location inside a garage.
Thank you for your comments
-- joe78
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CWLee wrote:

flue gases depends on whether the furnace is in a confined space or an unconfined space. Your garage is probably leaky enough to satisfy the unconfined definition. You do not need any specific openings to the outside for combustion and dilutions in unconfined spaces.
In confined space, you need one opening within l2 inches of the ceiling and one within 12 inches of the floor for combustion air and dilution.
It is obvious from your description that the 4" x 6" vent has nothing to do with the gas combustion and dilution since it opens into the air distribution system and not into the garage directly. Therefore it's purpose is to provide fresh air to the interior and has nothing to do with combustion or dilutions of exhaust gases. The outside opening definitely should have a screen of hardware cloth of 1/4" squares followed by regular window screen to keep both animals and bugs out.
The solution to your question is simple. Construct a small sliding gate so that you can regulate the opening where it enters the "space." Or simply tape a piece of cardboard across the opening with duct tape. For example start by closing off 1/2 of the opening and see if there are any adverse effect, e.g., stuffiness, and if not close off 3/4 of the opening. How much you can close off is like to depend on how tight your house is--drafty house means close the opening off completely, very tight house means don't close off any of the opening.
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