Hardibacker cement board odor with big hot fires

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PDutro

New Member
Sep 26, 2021
67
Oregon
Running our newer RSF Focus 3600 finally now that temps have cooled. Ran it all day yesterday kept a medium fire going, and at night I built it up with some bigger splits. For an hour or so when the fire was really ripping there was an odor that I traced back to the area directly above the front of the fireplace and it smelled like what I remembered the hardibacker smelling like when it was freshly installed.

Checked surface temps with my IR gun, the hottest reading I got was 240 half an inch directly above the fireplace. As I moved higher (2-3 inches and above) temps cooled down to 150 and lower as I measured higher up on the wall)

All other areas of the chase when measured with the IR gun were 90 degrees or under.

Wondering if anyone else has a clean face install with hardibacker, and whether the smell lessens over time?
 
Last edited:

GrumpyDad

Minister of Fire
Feb 23, 2022
766
Champion, PA
Running our newer RSF Focus 3600 finally now that temps have cooled. Ran it all day yesterday kept a medium fire going, and at night I built it up with some bigger splits. For an hour or so when the fire was really ripping there was an odor that I traced back to the area directly above the front of the fireplace and it smelled like what I remembered the hardibacker smelling like when it was freshly installed.

Checked surface temps with my IR gun, the hottest reading I got was 240 half an inch directly above the fireplace. As I moved higher (2-3 inches and above) temps cooled down to 150 and lower as I measured higher up on the wall)

All other areas of the chase when measured with the IR gun were 90 degrees or under.

Wondering if anyone else has a clean face install with hardibacker, and whether the smell lessens over time?
That seems really warm to let hardibacker get to, im not a pro like many others here but are you sure you met the minimum clearances required by your stove manufacturer for all six sides? Remember that hardibacker doesnt reduce your clearances to the wood that it is screwed to. You measure from the wood to the stove and ensure you are within spec of the clearances for your stove per your manufacturer. There are TONS of people that believe that they can just slap hardibacker over studs or wood paneling, then put tile or stone on the hardibacker and ignore the clearances. Hardibacker does not do anything to stop the heat from reaching the wood behind the hardibacker, if anything all it does is slow the initial transfer or heat in / out from the wood behind the hardibacker.
 

PDutro

New Member
Sep 26, 2021
67
Oregon
That seems really warm to let hardibacker get to, im not a pro like many others here but are you sure you met the minimum clearances required by your stove manufacturer for all six sides? Remember that hardibacker doesnt reduce your clearances to the wood that it is screwed to. You measure from the wood to the stove and ensure you are within spec of the clearances for your stove per your manufacturer. There are TONS of people that believe that they can just slap hardibacker over studs or wood paneling, then put tile or stone on the hardibacker and ignore the clearances. Hardibacker does not do anything to stop the heat from reaching the wood behind the hardibacker, if anything all it does is slow the initial transfer or heat in / out from the wood behind the hardibacker.
Thanks for the reply. The whole area was opened up, reframed for the fireplace per manufacturer specs and passed inspection before it was closed up. As far as that goes I’m not concerned.

It’s just the area immediately above the fireplace where convected heat is moving out into the room. The hardiebacker is rated fireproof at 1500 for an hour or something. Given that everything was done to spec my concerns with the temps in that area are more about the odor.
 

EatenByLimestone

Moderator
Staff member
How long has the stove been in? Could you be smelling something else? I've never heard of anybody smelling Hardibacker. I've used it in a hearth, I'm not sure how hot it might have gotten, but I never smelled it.
 
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PDutro

New Member
Sep 26, 2021
67
Oregon
How long has the stove been in? Could you be smelling something else? I've never heard of anybody smelling Hardibacker. I've used it in a hearth, I'm not sure how hot it might have gotten, but I never smelled it.
Yeah, I’m beginning to wonder if what I’m smelling is either the paint we used on the clean face wall around the fireplace getting hot and off gassing, OR maybe we are still getting some burn-off of manufacturing oils and stuff like when we had with our first few fires. It could be that I’m tracing the smell back to the area right above the center of the fireplace because that where the convected hot air comes out.

I checked with Hardiebacker, their cement boards won’t even burn below 750 degrees, and won’t ignite below 1500. So I’m thinking 240 surface temp in that one small area is not something to worry about.