Insulating

I haven’t yet decided between a bell design, or traditional. However, I would like to know a couple of answers to two specific questions, please.

First is two parts. I’ll be building onto a wooden subfloor. What would be the best insulator to keep from any heat damage? Also, what would be the minimum, yet 100% safe thickness of said insulator.  I’m asking purely about the type and thickness of insulator to line the bottom. I have enough research material to plan the rest of the build’s insulation and thermal mass.

Secondly, I do understand that an indoor chimney is more than necessary for absolute draw. If, and I do mean this purely hypothetical unless it is possible, I were to throw the chimney horizontally outdoors, then 90° upwards, would any type of pipe insulation be sufficient for good draw?  If it is more possible with a bell type, or traditional, please elaborate on that, if you don’t mind.

I really do appreciate any help, and I’m thankful for this forum and for the Wisner’s invaluable teachings.

Mike, I've used 1/2" subfloor cement board covered by sheet metal or even thicker steel if you can find it. Also it's nice to extend the steel out in front of the stove to protect and fireproof the floor. The area around the stove can get a lot of abuse depending on the user. In rentals people chop firewood and kindlng in front of the stove and do damage to the floor. I would be looking underneath the crawl space to see if the floor is supported well. Also sheet metal, metal roofing scraps, on the walls behind and beside the stove is a old method of making a heat shield.
If you think the floor will get hot pour a thicker concrete pad on top of the subfloor. If it's an extremely heavy stove you need to cut out the floor and pour a pad on a footing on the ground.  
I have insulated a outdoor stovepipe with perlite held in place over the stove pipe by cheap ducting. You might want a Tee at the bottom for a clean out unless it's easy to remove. It should be cleaned at least every season. A quick way to support a outside stovepipe is find a scrap of water pipe or irrigation pipe, bury it a few feet deep, and wire the stovepipe to it.
Jeremy

Thank you very much, Jeremy. I had planned on ensuring it is supported well in the crawl space. While I’m doing that, I may as well do the steps you mentioned. It’s own footing, and all.

It’s nice to hear that an insulated chimney will work outdoors. I was thinking of just using insulated pipe wrap, thinking it doesn’t get hot enough for perlite. However, I need to be secure in my work, so I like your ideas.

Thank you very much for your time in helping me with my questions. I really do appreciate it.

Mike

Insulation does not prevent heat transmission, it just slows it down. In order to protect a wooden floor, you need to allow the heat to escape before it gets to the floor. Raising the concrete board mentioned above on bricks spaced several inches apart is a good way of doing that; free airflow will carry the heat away and protect the floor (and give a bit more usable heat to your space).

Thanks for the info, Glenn.

Just to reiterate what you had said... would they need to be fire bricks at that point? Would a couple of inches of space be enough of an air gap? If so, would half bricks be enough of a gap? (Half width)

Also, I’m assuming the main need for the air gap is under the burn box/riser section. If I do traditions bench, would I need those air gaps under the ducting section?  I feel the answer will be yes, mainly for the first run section of ducting.

You bet. Great design and build you are doing. Air gap might be a good safety measure. Just in case. I don't know what temperatures we are looking at. Steel is a good conducter so if it is oversized it can conduct away excess heat. Also is warm and nice to stand on. Your cat will love it. If the cat stops using it get the fire extinguisher ready. I did a steel floor over hot water tubing. It was great. Nice and cool in the Summer too.
If I built one I would be tempted to build in several temperature wells to insert long temperature gauges. And I definitely recommend the infrared temp gauges.

Jeremy Baker wrote:And I definitely recommend the infrared temp gauges.

I’ve been wanting to get a thermal temp gun for a while now. I finally have sufficient reasoning for it, haha.

I love your idea for the warm foot area, but at this point the work involved to minimize risk from it is too much for my feeble mind. I do have time to work these details out, so I’m definitely keeping it on my list of possibilities.

I finally found an older thread where Glenn explained how to utilize tin foil in the air gaps. I’ve certainly got my work cut out for me in these drafting stages. I have no doubts the cat is going to love this thing. Now I’m going to be extra cautious any time the cat isn’t on the thing. Haha.

Thanks again. You’ve helped me to feel a lot more comfortable in executing this plan.

Under the combustion core and 6-10" around it is critical to provide an air gap for free cooling flow. Under the bench is a good idea, especially near the core. Under the core I would use a full brick thickness (2 1/2"+-) minimum, though any kind of bricks will do the job safely.

Using a steel plate over the core can give a cooking surface, but elsewhere you will probably get better and safer results with a layer of cob or masonry. The sitting surface should not be allowed to get dangerously hot under any reasonable circumstances; metal might make high temperatures more likely. A 3" to 6" layer of cob depending on location will buffer heat flow appropriately.

Glenn Herbert wrote:Under the combustion core and 6-10" around it is critical to provide an air gap for free cooling flow. Under the bench is a good idea, especially near the core. Under the core I would use a full brick thickness (2 1/2"+-) minimum, though any kind of bricks will do the job safely.

Using a steel plate over the core can give a cooking surface, but elsewhere you will probably get better and safer results with a layer of cob or masonry. The sitting surface should not be allowed to get dangerously hot under any reasonable circumstances; metal might make high temperatures more likely. A 3" to 6" layer of cob depending on location will buffer heat flow appropriately.

Spot on, Glenn. I appreciate the time you’ve taken to answer my questions, and then some. I do believe I have what I need in order finish the drafting and start building.

Thanks again, everyone.

Mike

Good luck, and post pictures when you have something to show!