Insulation around riser

Micki Blanco wrote:Hi everyone...I'm building my first RMH and the perlite/clay inside my hardware cloth form surrounding the heat riser is loose and crumbly in some places.....like I maybe didn't pack it in tight enough. Is this a problem? Will the hardware cloth burn up and all my perlite fall into the manifold?

Micki Blanco wrote:Thanks for the timely reply Al! I am using the Bonny 8" blueprint as a guideline and have bought the RMH book. My bench sits on brick air channels with a 4" air gap from the wall. It is roughly 9'x3' with the end section about 2 ft wider from front to back to make a chaise. I do have a couple more questions.

1. I want to make a backrest to have soft cushions to lean against. Would it be better to make the backrest from cob or wood? If I use cob, will it be too much mass and reduce the heat from the bench?

1a)I will specifically send you to a second build done by E & E, that I helped on, thee backrest in that case has a 'Wattle and Dab' core and has held up very well ! Both will work fine, there are many
benefits to aWooden back which could be modified to make it adjust able at some future point, other wise have it custom built to your personal dimensions including an area dished to receive your
backside and heal rests !

2. I was concerned about having too many turns in my duct work, so the chaise part of my bench has no duct in the front section (maybe I can post a pic) I am wondering if this will reduce heat also.

2a) It certainly will reduce the heat in that area !

3. Since I'm a girl I'm already thinking about making it pretty...do the cushions have to be 100% cotton inside and out? I promised hubby I wouldn't burn the house down... so your help is greatly appreciated!

3a) Wool is more fire retardant than cotton, has a higher ignition temperature and can be more springy to sit lie on, This is a personal choice based on how various grades of wool feel next to your skin
and also what you nose thinks of the smell of the finished product,and the finished product depends on what your nose and skin tell you !

4. Do I have to wrap the ducts in cob? Or will sand be just as effective with bricks and rock for filler?

4a) Sand is easiest but it is slightly insulative, to absorb ,hold, and reradiate out the same amount of heat energy that you can create with wrapping the duct in Cob, and then adding a topping of Rock and Cob Lasagna
requires more thermal mass if made with sand !

5a) watch the video and tell me what you think !

https://permies.com/t/25435/rocket-stoves/video-great-rocket-mass-heaters#320868

Thanks, Micki

allen lumley wrote:

Micki Blanco wrote:

4. Do I have to wrap the ducts in cob? Or will sand be just as effective with bricks and rock for filler?

Micki, the problem in using sand without a binder (clay, fire clay, etc.) is that loose sand has lots of air spaces and is thus insulating. So you'll want to mix in some clay with your "masonry grade" sand.

Micki Blanco wrote:Thanks everyone for the info. I will use mason sand/clay 70/30% to coat the ducts and fill all the voids, using as much rock and brick as I can, lasanga style.

Micki Blanco wrote:With brick air channels, felt, 2layers of aluminum foil, and 2" of perlite/clay under my combustion chamber....how hot will the floor under the chamber get?