Ducted HVAC in Garage?

[Jandrews]

In our current home, built around 1980, we have HVAC ducted directly from our furnace/heat pump into the 3-car garage. Obviously the garage is finished, and has insulated doors, but this is a completely AWESOME setup. It stays near 60 degrees year-round, and I generally keep the registers closed. There are two regular registers, and when closed they leave just enough heating or cooling in to keep things nice. There is a doggie door, which is not insulated, so I am sure there is some minor leakage, but overall it is an incredibly nice space, similar to the rest of the house. The current house is all electric and the electric bills are never over $300 per month, and much less most of the year.

Now, for my question. We are building a new house, somewhere in the neighborhood of 3X the cost of the current house. New house will be somewhere around 3.600 sf finished, not counting the basement. It will have a 4 car finished garage with two double overhead doors. I have requested ducted HVAC in the new garage, since it works so nicely in our current house. My contractor has been squirming a bit from the first time I mentioned this request, and is now trying to get me to just go with an overhead electric heater. I am pushing back because that doesn't meet my needs at all, I want integrated heating AND cooling, and the overhead is not what I was looking for. His reasoning is that the ducted HVAC will be "inefficient", "won't provide return air to the furnace because of the firewall requirements", "will be a slave to the house thermostat", and on and on. I think there is a building code requirement for "fire damper" registers - which our current house does NOT have, but that seems like a very small issue to me. I am willing to pay to get this done, but he just seems very resistant for some reason. I have related the excellent arrangement in our current house as proof that this can work VERY well, but he just seems to be in dis-belief or uncomfortable with going this route for some unknown reason.

Can any contractors or building / HVAC experts here weigh in on this? Is there any reason why I couldn't / shouldn't have integrated heating and cooling in my new 4-car garage?

Thanks in advance. By the way, we have been struggling with our contractor's reaction to this request, so my wife finally said, "why don't you post it on Pelican OT and see what they have to say". Pretty powerful community here, wouldn't you say?


JA

[Scott R]

I just finished heating my garage, (the thread is here in OT somewhere) and I originally wanted to go with a feed from the main furnace. HVAC guy said "no way" reason given was that he could not easily cross the garage firewall/barrier with HVAC duct. I found this strange since my last house had ducts to the garage, same as yours. It turns out after looking into it, that somewhere in the 90's they started with these garage fire breaks, and that causes the issue.

That being said it can be done, however I was told it was infinitely more complicated to bring it to code. In the end I ditched the HVAC contractor because he did not seem to know much, and I installed a hanging gas furnace.

I really wanted to subscribe to your thread in the hopes that a more knowledgeable contractor replies, because I felt I was getting the run around as well.

[Jandrews]

Thanks for the reply, Scott. It sounds like yours was a retro-fit, and I can understand the possibility that it would be complicated to route the ductwork and still meet code. Let me know if yours indeed was a retrofit or if you were building a new house.

For my house, we just poured the foundation. There is zero framing done yet, so I would think there would be plenty of options to intelligently plan ahead a ductwork scheme that would meet code. But, I'm no expert, so I thought I would get a broader perspective from this community.

Thanks,

JA

[Scott R]

Originally posted by Jandrews
Thanks for the reply, Scott. It sounds like yours was a retro-fit, and I can understand the possibility that it would be complicated to route the ductwork and still meet code. Let me know if yours indeed was a retrofit or if you were building a new house.

For my house, we just poured the foundation. There is zero framing done yet, so I would think there would be plenty of options to intelligently plan ahead a ductwork scheme that would meet code. But, I'm no expert, so I thought I would get a broader perspective from this community.

Thanks,

JA

It's a retro, which is another reason I'm interested in your thread. If they say they can't do it on new construction either I'll fell a bit better.

[Porsche-O-Phile]

You have to check the codes regarding occupancy seperations. I'm not an expert on residential (do commercial work only) so maybe it's okay, but I'd think that punching holes between habitable spaces and non-habitable spaces might give you some problems. Not to mention the potential for fumes getting in, etc.

You'll have to meet energy code in any case.

[VincentVega]

Any and all fumes from the garage can/will be distributed throughout the house. Not to mention fire issues.

Install a gas forced air system ducted out the wall or roof.

[turbo6bar]

What's the square footage of the garage? One option is a dedicated system for the garage only. You might be looking at a simple 1 ton unit. I don't even know if they make 'em that small.

Another option is the non-ducted split systems. You have an outside-mounted condenser and indoor wall-mounted A/C unit (like you'd find in an older hotel/motel). The heat is electric. The cost is generally very good. I've seen the units on eBay for less than a thousand dollars.

Those two options would separate the house from the garage and give you more control over the garage environment.

[LakeCleElum]

I'm just finishing build a retirement home that is 2,500 sq ft and a 4 car garage. I have a heat pump and my heating guy declined to duct into the garage for the same reasons provided above.

He did mention, that maybe he could come back and "add" a duct after I got my final inspection. I have an old wood stove I'll probably put in after the inspection, my neighbor has one and it keeps his huge shop very comfortable......Also looking at web sites to build a stove that burns used motor oil.......G'luck...

[lonewolf]

i had the overhead gas radiant heater in my 2000sqft garage. worked awsome .it was on a thermostat and was cheap to run. and when you need it ,it puts out a lot of heat.

[Jandrews]

** duplicate post **

[Jandrews]

Thanks for the feedback, guys.

Two things come to mind so far: "Any and all fumes from the garage can and will be distributed throughout the house". I get that, but what fumes are we talking about? If someone left a car running in there with the door closed, obviously that would be an issue. But realistically, are there any fumes coming from a parked/turned off vehicle? Would the ductwork with "closed" registers really be any worse than the door going from the garage to the house? I do understand the fume issue, but I guess I am thinking of the garage as a living room with a car parked in it. I may be off base here, and underestimating the "danger" of a parked car.

The other thing that I am concerned about is AC. I wouldn't mind going with a hanging gas/electric heater, but that only satisifies half of the equation. If I then have to intall an ugly "window unit" air conditioner, it will really feel like I am cobbling up this nice, new residence. By the way, the sf of the new garage will be a little over 2,000 sf.

Thanks for all ideas and comments...keep them coming.

JA

[turbo6bar]

2000 sf? Separate ducted split (A/C and forced air heat). You'll need 3 to 4 tons to cool that area anyway, so why not separate it from the house.
jurgen

[Jandrews]

Thanks Jurgen,

So when you say "separate ducted split (A/C and forced air heat). You'll need 3 to 4 tons to cool that area anyway", are you basically just suggesting to duplicate the setup that is heating and cooling the house? Same complete set of components, i.e. duplicate furnace, heat pump/condenser? Any idea what a "3 or 4 ton" unit would cost to install? How will that compare in size to what I will have for the house?

Thanks,

JA

[scottmandue]

I have been out of the biz for a while but...
Fire dampers are a must, they would have to be installed in the fire break wall.

If it were me I would put a small forced air gas heater in the garage. Make sure it is rated for heating AND air conditioning (need to have a two speed blower). Build a small platform in the corner of the garage. Cut a RA grill in the front or side and a hole in the top for the heater to sit on, cut a small fresh air grill to the outside and put heater over RA hole. Set A/C coil on top of heater, set plenum on top of coil. Run duct from top of plenum to rafters and duct out to two or three supply grills overhead. Plenum and duct do not need to be insulated because they are in the air conditioned space. Then run copper from coil to condensing unit out side for A/C. Run condensation pipe from coil to out side (flowerbed is okay). If you leave the heater freestanding it will be fine but if you build a closet around it you will have to put in combustion air grills to the outside. You will also need to run the vent outside and bring gas and electricity to the heater plus electricity to the condensing unit outside.

Of course the codes in you area may contradict part of what I have described. I presume you would have a contractor install this and sooner the better so you could have the electrical/gas/vent installed before the house is finished, you will need a concrete pad for the condensing unit also.

[rick-l]

No gas? A Modine Hot Dawg heater would be the ultimate luxury in my garage.

What about heating the floor with water in plastic pipe in the concrete?

[CurtEgerer]

Heat ducts to the garage are not allowed by the Code because they are dangerous. 'Fumes' include not only a running car but things like gasoline cans, solvents, paints, etc. There are also issues of sizing the furnace properly to account for probably 25% additional square footage and figuring out how to balance the supply and return air.

BTW: it is illegal in most jurisdictions to install a solid-fuel burning heater (i.e. wood-stove) in an attached garage as well. Yes, people do it all the time. Sometimes people are lucky and they work, other times there are fairly impressive explosions and fires .... Here's one I looked at a few days ago - note the melted vinyl siding on the neighbor's house some 75 yards away .... now that's impressive!

[turbo6bar]

Originally posted by Jandrews
Thanks Jurgen,

So when you say "separate ducted split (A/C and forced air heat). You'll need 3 to 4 tons to cool that area anyway", are you basically just suggesting to duplicate the setup that is heating and cooling the house? Same complete set of components, i.e. duplicate furnace, heat pump/condenser? Any idea what a "3 or 4 ton" unit would cost to install? How will that compare in size to what I will have for the house?

That's right. You can install a totally separate heating/cooling setup to control the environment in the garage. Generally, you want 1 ton (12000 BTUs) of cooling for every 400-600 SF. The actual ratio depends on various factors, but if you're just trying to knock the chill down in winter and brind down heat levels in summer, you could go with 600+ SF per ton, so you'd want something like a 3 ton heating/cooling unit.

I'm guessing a 3 ton unit would be around $3500-4500 for equipment and installation. That's just my guess. You need to get quotes. Plus, your installer should give you some advice on sizing for that space.

As far as how that compares to your house, it depends on your house size. If you're conservative, go with 400 SF/ton. A 2800 SF house may need two units for the interior, a 4 and 3 ton, for a total of 7 tons.

The heat pump is ideal for the garage, because you have no open flames.

[Jandrews]

It sounds like there are some reasonable concerns expressed here with regard to fume and fire danger. Ok.

If I ditch the idea of ducted HVAC, and I go with a gas overhead heater, what are my options for AC? Clearly the split forced air / heat pump that Jurgen suggests would be ideal, but I'm not sure I want to put that much money into it. We will keep three cars in there, including the 911, and a custom motorcycle. I plan on utilizing a portion of one stall for nice tool storage and workshop space. Also plan on having a kegerator and possibly a couple stools for hanging out, along with nice framed pics/posters etc...

What can I do for AC?

Thanks,

JA

[turbo6bar]

2 words: ductless split

A quick search on eBay reveals several 1-2 ton models. I spy 1 two ton model for $1200 + shipping, and there are several cheaper models. That would keep your garage cool, but not 75 degree cool. That's your best bang for the buck without looking too ghetto for a Porsche guy.

[Porsche-O-Phile]

I was thinking about this some more. . . I believe there's a one-hour rating requirement between habitable spaces and garage/non-habitable spaces in the code for most residences. As such, you'd definitely need a fire damper on the duct. You also need to have a way to access the damper - that way if it ever trips, a guy can get up there and replace the fusible link and reset it. If it's located above a hard-lid (gypsum board) ceiling, this is a problem.

The other issues you'll have are these:

1. Fumes - obviously nobody with half a brain is going to run their car in a garage with the door closed, unless they're on a suicide mission. As such, there is little potential (but potential nonetheless) for CO (carbon monoxide) fumes to back up through the duct when the system is not operating. Consider also that there ARE some small levels of gasoline fumes emitted from even parked/non-running cars, plus you'd have small levels of fumes from whatever else you might have stored in there (gas cans, lawnmowers, cans of toluene or mineral spirits, whatever). Probably not enough to be harmful, but just something to consider.

2. Energy code. Depening on your municipality, these are getting pretty stringent - even for residential occupancies. Garages typically have ****ty insulating "R" values and you'll literally be heating the outside unless your garage is very well insulated or you're paying to upgrade the insulating value of the building envelope. Also consider this: If your thermostat is located inside (as it likely is), your furnace will run, heating the interior spaces to the level set on the 'stat. It will heat the garage to whatever level (probably some lower temperature value) as well, simultaneously. When the 'stat shuts the furnace off, the garage (due to crappy insulating value) will cool down quickly and cold air will back up through your ducting into the interior spaces, cooling them down and effectively reducing the value of the insulation in THOSE spaces as well. The t-stat will then turn the furnace on more regularly. You'll be throwing money out the window - literally.

I'm not sure about this, but some kind of "flapper valve" or backflow preventer in the duct would alleviate a lot of your problems. I'm not even sure these exist (I'd have to ask one of my mechanical engineers), but it kind of makes sense - something that would swing open when the ducts are pressurized with air (furnace "on") and then close/shut when the flow/pressure goes away. This would help somewhat.

If I were designing this, I'd seriously look at a seperate, stand-alone small furnace JUST for the garage (with seperate t-stat and controller). I'd also strongly recommend insulating the heck out of the garage with energy code compliant values appropriate for HABITABLE residential spaces (IIRC it's R-30 for the roof and R-12 minimum for the walls). In addition to the life-cycle cost savings this would give you and increased efficiency, it would make it a helluva lot easier in the future to convert some (or all) of the garage to habitable space in the future, since the energy-code issues are already addressed. . .

I'll ask a couple of M.E.s in my office on Monday about this if I remember for you - someone's got to be familiar with residential installations. . .