Unit Heater (NG Garage Heater) Placement Issue

[abeyersdorff]

All-

I have a Mr. Heater 80,000 BTU Big Maxx MHU80 heater. Manual calls for 18" clearance on panel side and at the rear. I have it installed near the corner of my garage as shown in the diagram below. I have seen many of these installed backed tightly into a corner at an angle. The inspector does not want to pass it because he doesn't consider the 18" rear clearance requirement to be met. Thoughts? Documents clarifying this need, hopefully in a way that will allow me to keep my heater as-is? Thanks in advance, I searched the forum but couldn't find an answer, apologies if it's been covered.

Aaron

[Admin]

I cannot find any workarounds in the installation manual.  You will likely have to maintain 18" clearance from the back of the heater to combustible material.  The inspector may let you reduce the rear clearance to 9" if you follow Table 4.1 from the B149.1-20 Gas Code.  Pic attached.  You would have to install 28 gauge sheet metal on 1/4 in insulating millboard, on the wall behind the heater.

4.13.2
The intent of Clause 4.13.2 is to ensure that appliances are not installed too close to combustible materials as to start a fire. Continued exposure to high temperature can lower some combustible materials' ignition temperatures.

Minimum clearances to combustible materials for appliances are specified in Clause 7 of the Code and are based on proven laboratory testing. Appliances may be installed with reduced clearances provided that these have been certified, the certification has been accepted by the authority having jurisdiction, and the clearances are marked on the appliance nameplate to enable field verification. Appliances may also be installed with reduced clearances over those required in Clause 7 provided that combustible materials are protected according to Table 4.1.

The only other option would be to turn the heater as only 1" clearance is required to the side, or relocate it further back, as show in the attached pic.

[NoDIY]

Agree with admin

[abeyersdorff]

Thank you.

That's what I was assuming was my best course of action. The metal barrier isn't an option as I don't have 9" to gain in that direction. I was waiting on hearing something different from Mr. Heater, hoping for some kind of diagram or language that would allow me to skirt this, but I doubt that will happen.

The worst part of turning the heater is I will have to revamp the venting considerably, but not the end of the world I guess. On that subject, anyone looking at this, I would heavily advise against using the Amerivent B Vent snap together products from Menards. Absolute garbage. I spent more time trying to get these 'slick snap together' sections together than on most other parts of the project.