We are ready to put the bench facing around the stove, do you recommend filling the space between the 8x8 flue tiles (directing the warm air) and the bench? I would like the bench seat to get warm, if I fill that space seems like it will take longer to heat up?
@dclaire , yes, we generally put masonry solidly around the bench flues (carrying combustion gases) with the thought that this will provide better conduction from the flues to the outside masonry of the bench. Air is a cool insulator. As I discussed with your team the other day, I have sometimes literally mortared right to the bench flues and skipped the expansion joint at the bench level because the temperatures are lower and the effects of the overall vertical expansion of the heater are minimal there… and I have also sometimes applied the expansion joint.
Hope that helps. Would be fun to see a photo of your progress! You could either post publically or send privately.
Our benches are 20" high, to fill that space with mortar seems like a lot of weight on the flue tiles?
@dclaire, 20” is a little higher than we usually make our benches which hover in the 16-18” range. If you consider that the slabs that you use for the bench top will span over the flue liners and be supported on the masonry either side, that’s a good bit of the weight off of them. Also, the fill you put over the flue liners (mortar and off cuts?) will form a kind of arch over the flue liner. If it’s not too late, you may want to lay one sheet of the 1/4” ceramic paper we supplied you with across the top of the flue liners so that they have some cushion from the masonry above.
I’m out of the 1/4 inch ceramic paper, but cut cardboard for the top of the flues. We put the bench that high to match the bottom of the firebox door.
I need more ceramic paper for the around the top clean out door to the space where the heat exchanger is. Can you send me a few scraps? I will also need it for around the top of the insulated space above the stove, or can I use cardboard there also?
In Austria and Germany it is common to build “air gap” heaters where there is a space between the core and the facing. With this strategy, like the double skin with the expansion joint one we recommend, you have a double seal at the core and at the facing.
As long as you ensure a good seal with the bench flue tiles and again when you set the bench slabs, you may consider just leaving the space without material in order not to put too much mass into it.
We’ll be happy to help you with your additional materials needs. Just give our office a call, (541) 632-3028.