Woodstove Pad Design

[MasterKraft]

Greetings!

We bought a house in Michigan about 15 years ago that had an old Sierra woodstove (70's?). Due to it's proximity to the living space we've decided to move it so we can allow for more room for seating in our living room. I've gotten most of the pad built per the instructions in the NFPA 211 section 13.5.2.1...

13.5.2.1 Room heaters, fireplace stoves, room heater/fireplace stove combinations, or ranges that are set on legs or pedestals that provide not less than 6 in. (152 mm) of ventilated open space beneath the fire chamber or base of the appliance shall be permitted to be placed on floors of combustible construction, provided the following conditions exist:
(1) The floor under the appliance is protected with closely spaced solid masonry units not less than 2 in. (51 mm) in thickness.
(2) The top surface of the masonry is covered with sheet metal not less than 24 gauge [0.024 in. (0.61 mm)].
(3) The floor protection extends not less than 18 in. (457 mm) beyond the appliance on all sides.

For the sake of discussion I've essentially poured a 2"+ thick concrete pad for the unit to sit on but I'm struggling to understand the reason for the sheet metal. Is there an approved design that I can implement to avoid having to use this? My plan to finish things out is to tile and grout the top and sides of the pad. That said, the layer of sheet metal adds a level of complexity to finishing with tile as I'm not sure of a solid way of integrating this in for a tiled application. Hoping someone here has some advice for me either in how to eliminate the sheet metal entirely from the design or how to integrate it in so I can have a tiled finish that will end up solid and not crack.

For reference, the current pad is 2" patio block sitting on a piece of 1-1/2" thick MDF installed in 1997.

Greatly appreciate any advice! Thanks!

 

[begreen]

I think the original intent was for the metal to form a uniform, non-combustible barrier to any sparks. This makes sense if underneath the metal there a loose-placed bricks with no grout. It also may serve to reflect some heat off the bricks. If there was micore or fiberfrax board under the cement, the hearth would be safer. Was the concrete poured on a plywood base? The insulation value of concrete is not high. Two inches is R=0.19, not great.

Is there a UL label on the back of the stove? If not, do you have the manual for the stove? That should specify the hearth requirement and clearances In lieu of this, the stove needs to have 36" clearance from the back wall unless an NFPA heat shield is put up. A modern stove will have closer clearance and easier to satisfy requirements.

 

[MasterKraft]

I think the original intent was for the metal to form a uniform, non-combustible barrier to any sparks. This makes sense if underneath the metal there a loose-placed bricks with no grout. It also may serve to reflect some heat off the bricks. If there was micore or fiberfrax board under the cement, the hearth would be safer. Was the concrete poured on a plywood base? The insulation value of concrete is not high. Two inches is R=0.19, not great.

Is there a UL label on the back of the stove? If not, do you have the manual for the stove? That should specify the hearth requirement and clearances In lieu of this, the stove needs to have 36" clearance from the back wall unless an NFPA heat shield is put up. A modern stove will have closer clearance and easier to satisfy requirements.

Thank you for the reply.

The stove is about 40 years old. I wasn't left a manual when we bought the house and there is no UL label on the stove. As a result of this I've been following the NFPA rules exactly for unlisted stoves. The concrete was poured onto a layer of 1/2" cement board. Since the NFPA doesn't talk about insulating values in the pad design I didn't give that any consideration. I was simply following the guidelines set forth in the NFPA manual.

I could see some reflectance properties but metal is a superb conductor so I would expect MORE heat to be pulled into the base than if it was left out and an uninterrupted based of nonconductive material was provided. Granted the piece of metal is very thin.

Nevertheless, most of these properties would be negated if I tiled over the sheet metal. Just doesn't make much sense to me.