New home: furnace in garage

[dallasbill]

Frist of all, my aplogies if this has been addressed -- I tried search and did not find anything.

We are in the midst of building a new 3000 sq ft ICF home here in Dallas and it will have 2 gas furnaces. One in the front, and one for the back vaulted area w/ 2nd story studio and room over the garage. We have had an energy audit, etc. of the design by an engineering firm specializing in such things so I am not concerned about insulation, zoning, tonnage etc.

What I am seeking more info on is the placement of the 2nd zone's gas furnace -- our GC is planning on placing it in the unconditioned garage. It will be in an enclosure suspended from the 8 foot ceiling there, against the corner of the back wall next to the interior wall of the attached garage.

I would appreciate it if anyone could relate to me the do's and don'ts of such an installation in a garage, as it's new to me -- I come from the land of basements! Things such as air supply -- is it just from the garage? Plus, are there any issues with "garage smells" we need to be concerned with entering the house?

I am a bit of a knowledge junky and like to be fully informed with what we are sinking a siginificant amount of money into.

Thanks so much!

[wolfdog]

Obviously I'm not looking at your house, but it would be a very common thing to put it in the attic space above the garage.

[Shophound]

I've seen upflow furnaces installed in a garage, and horizontals in the attic over a garage. Garage odors shouldn't enter the house if the return air plenum to the furnace from the house is properly sealed.

By the way, welcome to Big D. I've lived in this area most of my life...I hope you're ready for hot, muggy summers and winters where the outdoor temperatures swing all over the place.

What is ICF?

[beenthere]

Insulated Concrete Form

[Midwest]

Shophound- ICF is Insulating Concrete Forms. You've probably seen them since they've really gained popularity but maybe hadn't heard them called that. Basically, expanded polystyrene a.k.a. styrofoam enclosing concrete and attached to each other with nylon, plastic or metal ties. Lots of brands, types and styles out there. As with anything else, some better, some easier to use, some friendlier to other trades, etc. than others. Greg

[aircooled53]

You don't have anything to worry about, attic installations in the Dallas-Fort Worth area are very common.
But, I would suggest that you insulate the garage ceiling if your unit is installed there. Some G.C. do not insulate the garage. Make be a good idea to have ventaltion in the attic in that area also, ask the G.C. to have fresh air brought into air space in the attic..

[Steve Wiggins]

Originally posted by dallasbill
It will be in an enclosure suspended from the 8 foot ceiling there, against the corner of the back wall next to the interior wall of the attached garage.

This doesn't sound like an attic to me

Bill do you know if this is a condensing furnace or an 80%?

[dallasbill]

Thanks all! The welcome is appreciated, but I have been here 10 yrs -- but it's the first time we have built a house from scratch and the 2nd furnace positioning was puzzling to me!

I see that someone answered the ICF question. For those wanting more, the block we used is Amvic -- the 6" concrete core variety...http://www.amvicsystem.com/index.html

The space above the garage is a future media room and is part of the 2nd floor at the back of the house... no attic space there. That's why the 2nd zone furnace is in the garage -- space efficiency. I have been assured the return air plenum will be sealed with extra care.

BTW, the garage space is uninsulated in the traditional stick house sense. BUT 2 walls of it are 11" ICF walls (2.5"EPS foam, 6"concrete, 2.5"EPS foam) and 1 interior insulated wall and 1 garage door wall. So, there is a certain amount of thermal mass energy retained and a lot less air leakage than a full stick garage.

The HVAC sub says he has done this before and there will be more than enough combustion air available via the garage space without a vent to the outside. Is there any way to more accurately determine this?

And, I am checking tomorrow to see if it is an 80% -- I don't think it's a sealed super-efficient kind.

[johnsp]

Probably not. Especialy if there's no fresh air intake. How will the unit be vented? Sidewall out the back of the garage?

[dallasbill]

It is vented via a stack passing up through the sidewall and up through the roof.


RE: "Probably not. Especialy if there's no fresh air intake."

Sorry... what is this referring to?

[beenthere]

50 CF of free air for every 1000 btu's input of your furnace.

A 50,000 input gas furnace would require an area of 2500 cubic foot.

A 16' x 20' x 8' garage would have 2560 cubic foot.

[dallasbill]

beenthere... thanks so much! ;-)

I shall get out my tape measure this weekend!

[41gasman]

Dallas.
One thing to keep in mind with this location.
In the winter you are guaranteed a frozen
garage in that area.All that combustion air
is coming from some where you know.Most of
the 80% furnaces have a inducer blower motor
that move some where 65 to 80 cfm.
So your 2500sqf garage whould have a
complete air exchange with the cold out
side air every 32.0 min of furnace
operation.16'x20'x8'=2560 cubic feet.
2560 cubic feet/80 cubic feet a min.
(inducer blower)= 32.0 min.
Can you say cold!!!