Gas shop furnace emerg. shut off sw reqs..

[zinfendel]

I'm installing Ruud gas furnace in my detached shop. I have NG at my house. I will install, wire and flue the furnace, then have a licensed pipefitter make the gas connection. He will contact the local inspector to inspect the installation and approve it.

What are the requirements for an emergency shut off switch in this kind of install? The furnace will be along the back wall of a 22x22' building. In my last shop I put it fairly high on the wall (but reachable) and about 1-2' to the left of the furnace. Not sure what my rationale was, but the inspector didn't seem to mind.

New house, new town, same state (MA). I searched the web a bit and didn't find anything. Close to the furnace? Away? Near a door? The shop has a 100amp subpanel fed from the main in the house basement.

Thanks for any advice....

John H

[mdshunk]

The rule is "within sight". That means that the switch must actually be seen from the furnace location and be less than 50 feet from the furnace. It is fairly typical to screw the disconnect switch right to the side of the furnace, or on the wall adjacent to the furnace. Being able to reach the switch without the aid of a ladder would also be a good thing.

[zinfendel]

Thanks MD, I'll attach it to the side.

One other question on venting. The furnace (Ruud UDGA-100C-ER, 100K BTU) has a 5" top vent outlet. If I am venting straight (or nearly straight) vertical through the roof above, can I use an adapter at the furnace and use 4" pipe? I bought the furnace second hand and don't have any documentation for it.

Lastly, I will use Type B double wall pipe through the flashing/collar in the roof, but must I also use it where the vent penetrates the ceiling? I will have a 14.5" sq opening framed between the joists and the pipe can pass through the center of that.

Thanks for any advice....I *am* consulting my local building inspector BTW....

JH

[Wgoodrich]

The pipe is not allowed to reduce smaller than the outlet of the eqiupment. No pipe is allowed to be smaller than that outlet of that furnace.

No single wall pipe is allowed to pass through an attic. If in cold climate no sinlge wall pipe is allowed outside.

Where passing through combustible material an insulating thimble is required to be installed protecting that pass through location from combustable material.

Single wall would be fine in the room but before you pass through that ceiling you should go to multiple lining piping passing through the ceiling, through that attic, and while outside.

Hope this helps

Wg

[zinfendel]

Thanks WG.

A bit more research since I posted, an I have found that 5" pipe is required for my install. I have found "sizing tables" that show for my vents rise, lateral and furnace BTU output, that 4" will not cut it. That aside from the "no downsizing rule".

I have also found a supplier for 5" Type B double wall vent pipe that I will use from below ceiling in the shop space to 2-3' above the roof line.

As always, thanks for the advice and a great forum....

JH

[Wgoodrich]

Be careful not to become confused between sizing make up or combustion air intake vent sizing and exhaust [aka flue] venting. The two are calculated differently.

Be aware you must have combustion air addressed allowing air to feed the fire without endagering occupants.

The venting out the roof must be at least 2' above any roof surface within 10' horizontally of that flue vent.

Just some added thoughts

Wg

[zinfendel]

I'm not sure how the makeup/combustion thing works on this furnace. Like the Lennox propane unit in my old shop, there is a large intake/vent in the upper front of the thing above the burn chamber that allows for draft/dilution air. But there is no set up that I can see for specifically ducting in combustion air. It is clearly just take from the heated/living space.

Is this no longer acceptable? I know that the comustion air leaves the space and be made up somehow, but in this shop, I'm sure there are places air can bleed into through the structure such that I won't create a vacuum in there and affect the venting of exhaust. How is this addressed in homes where a furnace like this is installed in the basement?

JH

[Wgoodrich]

The calcualtion for using room air as combustion air is 50 cubic feet of area for each 1000 BTU rating of appliance. Room air is normally used. The makeup air intake tubes are needed in confined spaces or super insulated with less than normal air exchange of a building. Tightly closed low air infiltration areas or small closet type confined areas are when the make up air is required. Garage you should be fine just check the calculation above to ease your mind on the subject.

Good LUck

Wg

[zinfendel]

I'm a bit over the wire, for my shop size I calc 92K BTU and my furnace is 100K. Two std overhead garage doors and I'd think there would be enough "leak" air though?

"makeup air intake tubes", what are those? Just some additional venting from outside into the heated space? Or something that is directed directly at the burner??

JH