freah air for rocket stove in Hobbit Home.

[thehobbitguy]

Hello all.  long time builder, first time poster.

Built a 3x3 x 13 foot - 6 inch diameter - rocket mass heater in my shop.  worked beautifully, lots of heat.

Want to build one in my new Hobbit Home that i am building, and WAS planning on putting in a freah air duct ( 6 inch ABS ) under the footing and slab, up into the stove - bringing the air in from up above the 12 inches of dirt on the roof.  with a dedicated shut off to stop cold air infiltration.

Reading on here that this may not be a good idea...

Options or opinions ? The Hobbit Home will be 4 feet above grade, completly buried in a foot of dirt, except for the front wall, with minimal chances for air leaks...  it will have an ERV supplying freah air though ...

I would post pictures, but get the message that " this forum has reach its max your image was not uploaded".

Hobbit Home progress @ daves hobbit home build on Facebook, or google "undergroundandlovinit"

[stinwell]

First, you will probably need to clarify –it sounds like you are talking about ducting air directly to your stove for combustion, or are you trying to provide make up air for the building (which includes the stoves needed air indirectly) ?

I think most would advise against any direct to fire air supplies (myself included). There is a lot out there about this already.
(You definitely don't want ABS pipe anywhere near the fire. Besides the obvious with its relatively low melting temps, in theory any reverse flow carrying embers, sparks, and hot gases that causes any melting of the pipe can create flammable gases.)

Have you taken a look at the thread I started recently on make up air? Peterberg specifically describes his make up air set up that was run through a slab and sounds similar to your description, and it did not function as intended for him (which of course doesn’t mean it wouldn’t work for you). His info there may be helpful for you since you will be relying on the ERV anyway, so in theory if that is set up well you should be able to balance for the stoves needs that way already.

Dans experiences detailed in that thread also bring home the fact that without patient and thorough observation of where the building is actually wanting to draw air in, you may or may not choose (or even have) the right location. Or the right location may or may not fit in with the designs of your building/heater, or remain the right location through all conditions your building will be subjected to. It’s more or less impossible to know all the variables of your particular building and conditions that could affect the outcomes, especially during theoretical design stages. You may well have to build it to find out if it works or not.


Along those lines, as a builder I avoid doing basically anything possible under a concrete slab. Especially something I’m not 100% sure would function as intended.


My intuition tells me that above the roof is the worst possible place to try to draw air from. Your pipe is likely to act more like a chimney and will be subjected to the most extremes of temperature, wind, and pressure fluctuations up there. Not to mention putting holes in whatever you are using to seal below your dirt cover. Do some searching around the term “neutral pressure plane” to help wrap your head around some of the concepts.


Hope any of that is helpful 

[thehobbitguy]

Thank you. That does help.
After more research, i have come to the conclusion, that the vent is not needed.
I will have to install a CO2 detector though...