Ducting for Furnace in Garage

[65Stang]

How's this for a furnace location... It's heavy...

I am going to run some of the duct work for it prior to drywall, but has anyone done something similar? If so, what is the best source for the ducting? I am only running the supply and return about 5 feet each, so what would be best/practical, round vs square ducting, or...

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[rickairmedic]

Stang see if there is a ( sheetmetal shop ) in your area they make ductwork from scratch everyday and will have the best prices you will get on metal duct. I personally would do a simple return box on the return side that I could hook a hinged filter rack to the bottom of and on the supply side I would have them make me a 90* elbow to fit the furnace opening ( with turning vanes in it ) and simply run it straight across the garage from there . You can then get round duct ( takeoffs and endboots and registers ) with the round duct to run some vents out to wherever you want them in the garage . The last one I did in a garage for a buddy we centered the furnace in his garage rafters and put a box on both ends and just ran round duct to each corner of the garage plus one vent right above where he would stand if working under the hood of a car.He did have a small 1&1/2 car garage though so duct didnt have to go far. How big is your shop?


Rick

 

[65Stang]

My shop is 22 x 22. I will also be putting in a hard lid GWB ceiling at some point, so I have to consider insulation duct or not.

 

[redsky49]

Round ductwork flows air more efficiently than rectangular (a fluid dynamics thing). Rectangular ductwork is used due to space considerations, though the ratio of width to height on rectangular ducts should not exceed 4-1 (you don't want a 24x4 duct).

It looks like you have a good sized blower associated with the unit. Assuming your 2 car garage is roughly 22x22, I would extend a supply duct to the center of the garage and provide a single ceiling mounted diffuser. This would require only a 10-12 ft. throw for the air to reach the garage corners, and would simplify the light placement and reduce costs. Duct size and diffuser should be selected based on the output cfm of the heater. Given the cfm, duct size and diffuser can be easily selected.

To encourage good air circulation, I would locate the return air grille 12" above the finished floor, drawing cool air from the floor back to the unit. If you don't want to run ductwork down to the floor, I would place the return grille over in the corner of the garage. A filter/return grille will be easier to access than a unit mounted element (as Ric mentioned).

To reduce fan noise, as well as the noise generated by the furnace, I would recommend that the ductwork be soundlined and incorporate at least one 90 degree elbow on both supply and return. It's still a garage but quiet is better than loud. It also looks like a large heater for the space, but I don't know where you are located. Do you have any user selectable fan speeds?

I can't see from the photos how the unit is vented (it is gas-fired isn't it?) or where combustion air is provided. You will also have to provide a large ceiling access panel for unit service. Check which side of the heater is the service side.

Good luck with your project.

As always, offered only as opinion

 

[65Stang]

Red, great suggestions, thankyou! I have a buddy who does commercial HVAC and he suggested 14" round ductwork.

The unit can be placed any direction horizontal, I placed it so the access panels are at the top, very easy to get to. I will have an access door in the ceiling right next to the unit. I will be exhausting the unit out the back and up through the roof using double walled exhaust ducting.

I had planned on a diffuser mounted filter, not sure about where I am locating it. I would have preferred closer to the floor, but right now, I will have virutally nothing sitting on or close to the floor. No sure if it has variable fan speeds, I didn't check when I tested it out.

It is a very large heater for the space, I believe 60,000 or 70,000 btu, but it was fairly cheap and I already had the propane supply. My garage is basically 440 sf. I also have an attached 400 sf shop that I will be running a branch to. My thought was to be able to heat both of them or just one or the other.

 

[rickairmedic]

Stang Red just made a good point and I had to go back and take a secone look at your furnace from what I can see it looks like an older downflow furnace so your supply and return will be reversed from what wouod seem normal . I also noticed the way it is sitting up there it would be a bear to service as its laying on its back.. I might suggest dropping it down below the rafters as it doesnt look like it will fit above them on its side and simply hang it with some threaded rod and unistrut. This way the ductwork will also be below the ceiling and not need to be insulated any chance you know the BTU's of that furnace . I agree it looks pretty big for the space which is ok in a garage . We put a 100,000BTU furnace in my buddies garage thats smaller than yours and it heated the place up post haste .


Rick

 

[rickairmedic]

Stang I noticed you say access is good in its current position my question would be can you pull the squirrel cage out with it in its current position.


Rick

 

[65Stang]

Yes, it's an older downfloor would appear to be laying on its back. One of the reasons I went with it was that it can be placed in any horizontal position.. (that just sounds bad!). The access panels are currently on top and I have hooked most of it up already. I had thought about putting it below the ceiling, but decided against it due to the amount of space it would take up, the noise, and it would go against the "look" I am trying to achieve with the finished garage.

 

[65Stang]

Stang I noticed you say access is good in its current position my question would be can you pull the squirrel cage out with it in its current position.


Rick

I believe you are referring to the blower motor/assembly in the middle picture? Yes, it can be removed from that end even with a finished ceiling.

 

[65Stang]

Oh, and if I remember correctly, it's an American Standard. For only $230, it came with a very nice Honeywell touchscreen thermostat.

 

[nate379]

I'd lift the furnace up higher so you can get insulation in that area.

 

[rickairmedic]

I believe you are referring to the blower motor/assembly in the middle picture? Yes, it can be removed from that end even with a finished ceiling.

Stang yes the blower motor is what I was refering to and I know it looks like it will come out from the end fairly easy but most of them are actually slid into the furnace from the front on tracks . With that being said it will have to come out the front of the furnace and it looks like it might be tight with it that close to the roof. I would recomend checking it before making everything permanent . I have been doing service and installs for 20 years and I can tell you nothing is more agravating than trying to repair a furnace in a tight location. I go nuts when some stupid plumber puts his water heater to close to the front of a furnace in a closet instalation ( not saying plumbers are stupid ) but some of them are .I would hate for the blower motor to go out in a few years and for you to figure out then after its mounted up with all the ductwork that you cant get the motor out.


Rick

 

[65Stang]

Stang yes the blower motor is what I was refering to and I know it looks like it will come out from the end fairly easy but most of them are actually slid into the furnace from the front on tracks . With that being said it will have to come out the front of the furnace and it looks like it might be tight with it that close to the roof. I would recomend checking it before making everything permanent . I have been doing service and installs for 20 years and I can tell you nothing is more agravating than trying to repair a furnace in a tight location. I go nuts when some stupid plumber puts his water heater to close to the front of a furnace in a closet instalation ( not saying plumbers are stupid ) but some of them are .I would hate for the blower motor to go out in a few years and for you to figure out then after its mounted up with all the ductwork that you cant get the motor out.


Rick

Thanks for the red flag Rick, I'll take a look at it tonight!!

 

[65Stang]

I'd lift the furnace up higher so you can get insulation in that area.

Thought about doing just that, but I wanted to get all the clearance I could for the access panels. If this is the only area without insulation, shouldn't be too much of an impact. I am not using high R value ceiling insulation anyways.

 

[rickairmedic]

Stang no problem I just figured you would rather find out now than when the blower actually goes out .


Rick

 

[porschedude996TT]

I would check the installation instruction of any FAF to see what the clearance distances are. I see the unit is used and it would be better to have the original installation manual, but that may be hard to find.

The one I am putting in my shop right now requires 24" of clear space in front of the unit to service it. The motor slides out from the front. The other distances/clearances are zero on the back, and 1" to 6" dependant on the type of venting.

I too had little knowledge of ducting when I started and 1/4 of the way thru had a friend in the biz look at what I had done. He too suggested 14" round on the intake (Return) and 14" round on the outlet (Supply). He also wanted me to increase the size of the registers. Initially I was thinking about putting my FAF in the trusses like you are, but the access issue raised its’ ugly head and I found a better location.

My friend dropped off a plenum and two end caps and two start collars and instructed me to cut it in half and attach it to either end and install the start collars in the end caps of the side of the 1/2 plenum.

As far the weight, I removed the blower from the unit and it was much easier to handle, then I will install the blower when the unit is in place.

 

[65Stang]

I would check the installation instruction of any FAF to see what the clearance distances are. I see the unit is used and it would be better to have the original installation manual, but that may be hard to find.

The one I am putting in my shop right now requires 24" of clear space in front of the unit to service it. The motor slides out from the front. The other distances/clearances are zero on the back, and 1" to 6" dependant on the type of venting.

I too had little knowledge of ducting when I started and 1/4 of the way thru had a friend in the biz look at what I had done. He too suggested 14" round on the intake (Return) and 14" round on the outlet (Supply). He also wanted me to increase the size of the registers. Initially I was thinking about putting my FAF in the trusses like you are, but the access issue raised its’ ugly head and I found a better location.

My friend dropped off a plenum and two end caps and two start collars and instructed me to cut it in half and attach it to either end and install the start collars in the end caps of the side of the 1/2 plenum.

As far the weight, I removed the blower from the unit and it was much easier to handle, then I will install the blower when the unit is in place.

Good information as well!! I have been unable to locate the Manual online, but there is a sticker on the inside that indicates what the clearances are depending upon which horizontal position it is installed at. As for the clearance in front (top in my case), I have proper clearance to remove the cage/blower assembly, but only if I slide the unit 1.5' one direction, which is easy now, but not so easy one all the pipe and ducting is hooked up. Oh well, deal with it if it happens. This unit will most likely only be used for 3-5 months out of the year, and not continuous during those times.

I will probably have to fab up my own plenums for transitioning from the unit to the ductwork, but that's not a big concern, I just need to find somewhere that carries 14" duct. Man that's large ductwork.

 

[Mike in Ohio]

Furnaces are 1 thing I know very little about, so I am wondering about some things said in this thread.

1. Will there be any combustion or exhaust problems with the furnace laying on its back?

2. Someone mentioned hanging it from the ceiling. It looks like a normal residential furnace to me, would it hold together being hung from the ceiling if it was designed to stand on the floor?

3. How hot will the outside of the furnace get especially around the flue area in that enclosed space?

I'll probably think of more questions later. I love the idea of having it up ouy of the way.

Thanks alot, Mike

 

[65Stang]

Furnaces are 1 thing I know very little about, so I am wondering about some things said in this thread.

1. Will there be any combustion or exhaust problems with the furnace laying on its back?

2. Someone mentioned hanging it from the ceiling. It looks like a normal residential furnace to me, would it hold together being hung from the ceiling if it was designed to stand on the floor?

3. How hot will the outside of the furnace get especially around the flue area in that enclosed space?

I'll probably think of more questions later. I love the idea of having it up ouy of the way.

Thanks alot, Mike

1. This furnace can be placed in multiple horizontal posititions ( ) so it's not an issue. Some furnaces are limited in this capability. The exhaust basically goes straight back and up.

2. They make systems for hanging them and it's not uncommon. You can also just basically buiding a hanging floor rather that straps.

3. The furnace itself is insulated and does not get too hot at the outside. That said, there are minimum clearances required depending on the construction of the furnace. For the flue/exhaust, I used double wall piping made for this application.

Also, in the rafter space, it's actually well ventilated, more than if it was down below somewhere. And during the winter, it will actually be fairly cool as well.

 

[msturg]

I know I'm new here but I figured I might be able to offer some advice. I would consider for supply running large foam duct (duct work that is internally made of a foam fiberglass combo and is externally lined with a reflective covering) only need to run it 5' out into the structure. Then branch off from there with flex duct, 12" supply runs, with diffuser grills in the ceiling.

working with the flex and the "foam" ductwork will take half the time to install since everything has a lot more give, and the stuff is pre-insulated. 9 times out of 10 when we did an attic install this is what we did.

 

[thammel]

A comment on the insulation....you probably want the furnace to be in the heated zone, therefore you would not want insulation underneath it. I'd plan on insulating around it - the sides and above it. This will get more heat into the garage and extend the life of the furnace.

Tom

 

[mikes334]

That is great advice thanks.