M55 Insert Installation Clearances

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New Member
Sep 29, 2018
Baltimore, MD
Hey y'all,

I've been reading through tons of threads on the forum trying to wrap my head around what I'm trying to do.

We had a gas direct vent fireplace in our house. It generated very little heat, so we've decided to replace it with a pellet insert, and have landed on the Enviro M55. I've gone through the installation manual and am currently working on building our a hearth pad. Once I finish with the pad, I'm going to work on framing out the enclosure.

Now, the manual states on page 23 "this enclosure must be a minimum of 18" deep, 36" wide and 23-1/4" high and made with noncombustible cement board." Makes sense to me. However, the current doghouse I have is 24" deep, 52" wide and 44" high. As such, I've got two questions:
  • The guy at the store suggested that having a little bit of breathing room for the unit never hurts, so can I just slap backer board on the pre-existing studs and call it good?
  • Assuming I leave the interior of the enclosure at it's initial dimensions, I'll need to frame in the opening. Should I shoot for exactly 36" wide x 23-1/4" high, or can I give it an inch or two of space, since the face of the unit is much larger than the opening and will cover any gap? I just don't want to cut it too close and screw myself
  • Finally, my wife was wondering, should we tile the wall around the unit before it is installed, or is there a chance said tile could be damaged, and we should pull it out on its service rails after installation to do tile work?
Thanks for helping out the new guy on the block!

Former Farmer

Minister of Fire
Apr 12, 2008
NE Wisconsin
If you read on page 17 of the manual, the insert frame has leveling and anchoring bolts on it. I would make the opening just a bit oversized so it can be leveled without any problems.

I don't think you would hurt the tile during installation, but why take a chance if you don't have to. If you do it after, you may lay out tiles a little different than if you do it before hand. How will the grout lines line up with the surround? May effect the look of the finished install.