Shop heater vent location

[Shran]

I am installing a gas shop heater in my building. The building is a 30x40 and the long walls are 40' long and the peak runs the length of the building. I have determined that I want the heater in the northeast corner and positioned at a 45 degree angle so that it blows towards the garage doors on the south wall.

This leaves me with somewhat of a dilemma about how to vent the thing. Initially I was going to do 4" Class III stainless horizontal through a wall until I saw the price of the materials. So my cheap option is to use 4" B vent through the roof. According to the thing I found, the top of my vent stack needs to be 2' higher than anything within 10' so that basically means a little less than 8' of B vent.

If I stick the thing in the corner, with the corners of the heater about 18" away from the walls, my vent stack will be less than 2' away from the edge of the roof, and it also means I have almost 6' of pipe above the roof line, which is fine, but that's 2/3 of my vent stack and it doesn't seem like it would be supported very well from wind blowing it over or something.

What would you guys do? I guess I could move the heater to the middle of the East wall or somewhere around that area so that more of the vent stack is supported by both the shop ceiling and the roof and I just have less total sticking out...

 

[RonD]

Use 3 guy wires on the 6' stack

Don't forget ceiling fans or the peak area will be the only "toasty place"
Reversible fans are best, sometime blowing the air up works better in forcing the warmer higher air down around the edges

 

[Shadowrider6661]

Myself, I would go through the rear wall and use a 90° elbow. This way, use can use mounting standoffs on the wall. This way there's no damage done to your roof, no water leaks. This is just one of those "Unsolicited Advice " moments we all have to tolerate.

 

[snoranger]

What about just running the pipe inside the building closer to the peak so there’s less height outside that you need to support.
Kinda like this...

 

[Eddo Rogue]

Heat rises.

 

[Rick W]

Use 3 guy wires on the 6' stack

You are only going to install it once, but then you’re going to use it 200 days a year for the next 30 years. You should locate it where it makes the most sense for your shop, and not where the vent would be a little bit more convenient to put in.

I agree with @RonD, but make sure you use aluminum or stainless or even copper wire. & don’t just connect to a single screw, it’ll shake loose and leak. I’d use something like the loop of a padlock hasp (loop mounted on a plate). I’d put gasket seal under it, drill the holes, fill the holes with gasket seal, work it around in the hole with a tooth pick, coat the screw, and then screw it in, and then cover the head. Stainless or brass screws. I don’t know how long it will last, but my Dad and I did this on top of my Mom’s house overlooking the Hudson River (harsh weather/winds) about 60 years ago, and it hasn’t leaked yet! & If you don’t have a passion to be on your roof, pop rivet everything. Screws shake loose. This’ll take you an hour more now and last forever.

If you don’t have your heater yet, I would buy a bigger one than you need. If you’re like me, I head out on short notice sometimes. The big heater helps it heat up comfortable very quickly. And if it’s on a thermostat, it really doesn’t use any more energy. If you divide the extra cost by the thousands of hours you’ll be using it…

My shop is about 27 x 48, wood frame, not insulated. I got a used home furnace from the scrap pile at the local heating and air supply house ($0.00, fit my budget, I’m cheap). Some HVAC guy, he’s probably driving a new Cadillac, talked somebody into getting a new unit when the only thing wrong with this one was a bearing on the squirrel cage. It cost about five dollars. He took all the relays and such, so I had to replace them. It’s 115,000 BTU. That’s actually hotter than the original furnace in the house before I added the second floor.

My garage door is in the short wall. I mounted the heater 1/3 of the way back on the right, pointing from right wall to left wall. I put a sloppy 45 degree diverter pointing towards the back left to create a gentle swirl around the shop. I have buddies who have put their heaters in to be pointing right at where they would be working at the bench or on their cars, and they are roasting when it’s on or freezing when it clicks off, and hate the draft.

Finally, I did the same thing I did on my air compressor, I put on one of those $8 eBay mechanical rotary switches on the thermostat circuit (not the power). I haven’t touched the thermostat in five or six years. I bought a 24-hour timer, and I just turn it to how long I think I’m going to be out there. That way, I never forget to “turn it off.” This one is for 240v, but remember all it is is an on off switch in series with the thermostat. It’ll never wear out! If I had it to do over, I would have run a couple wires to the house with a second timer, so I could turn it on before I walk out there in the cold!!

My 2cents, hope it helps!

EDIT: I put the thermostat right underneath the inlet side of the furnace. In that location it keeps the whole place at a relatively uniform temperature because it’s not being affected by the output directly.

 

[Shran]

Use 3 guy wires on the 6' stack

Don't forget ceiling fans or the peak area will be the only "toasty place"
Reversible fans are best, sometime blowing the air up works better in forcing the warmer higher air down around the edges

I'll have to run guy wires for sure, I think they're necessary for anything over 5' tall and I'll have at least that much sticking out of the roof no matter what. I think I'm going to be OK with a 5' stick of B vent on the bottom and then a 3' stick on top of that... I wish I could get longer sections. 8' would be nice. But at least with the 5' stick on the bottom I won't have a joint in the attic space and hopefully that will make it a little more rigid.

Thinking about fans - not sure what to do there. My ceiling is only 10' tall and if I've got my little tank top propane heaters going for a couple hours, it gets pretty toasty even down by the floor. I'd put fans in for sure if I had 12' or higher ceilings.

Myself, I would go through the rear wall and use a 90° elbow. This way, use can use mounting standoffs on the wall. This way there's no damage done to your roof, no water leaks. This is just one of those "Unsolicited Advice " moments we all have to tolerate.

I really thought about going out the wall but the Class III vent is stupid expensive. Like every piece is $50 or more, it's at least 3x the price of B vent through the roof.

I can't go through the north wall, the wind usually comes out of the northwest and the heater manual says if horizontal vent is used, don't put the exit on a wall exposed to prevailing winds. East wall would probably be OK. I'm fine with going through the roof, my logic is that if it's sealed correctly it's fine... if not it'll be evident pretty quick when it drips all over. If water gets through a hole in the wall from rain running down the building or something, it could be inside the wall for quite a while and depending where it runs out, you may never know until stuff starts to rot out.

What about just running the pipe inside the building closer to the peak so there’s less height outside that you need to support.
Kinda like this...

The heater I got hangs from the ceiling... I would totally do that if it sat on the floor. As it is I think I only will have about 14" of vent stack between the heater itself and where it goes through the ceiling... I did think about an angled run inside the attic to bring it out closer to the peak. I'm not sure if that would help because just a straight run upwards and out would have support in two spots right on top of each other, where as an angled run would kind of only be supported in one spot. Maybe that's not such a big deal, I may be overthinking this a lot but I want to get it right.

@Rick W I got an 80,000 BTU heater. My shop is 30x40 and pretty well insulated... according to the sizing chart I found, I could have got away with a 50,000 BTU model, or I think the next size up was 125,000. I shot for the middle, I think it'll work out well because it won't always be running and won't short cycle either.