Increased Riser Length

First of all, thanks to all those who have taken their time to post to, and manage this site.  Permies provides a tremendous wealth of varied knowledge, and clearly a labor of love.  

I have searched through much of the knowledgebase here, but have not found a clear answer to my issue - What happens if you extend the riser in a BBH with masonry bell?  

I don't have enough headroom in the camp to install a normal size riser (6" system) and still be able to reach a white oven in the top of the bell.  So I need to put the firebox in the cellar.  I plan to have the feed door around waist level for easy loading.  But that means I'll have a gap of nearly three feet between the top of the riser and the top of the bell.  

If I make the top of the first bell just large enough for the oven (hopefully about 17x17x14h) and the required gap around it, I think it will heat up better with less distance between the bottom of the oven and the top of the riser.  The second bell will include a small bench for room radiant heating and back-side warming.

Can I extend the riser without adversely affecting the burn characteristics of the heater?

Hi Randy,
First and foremost: in real world practise there isn't such a thing as a too large top gap, the distance between the riser's end and the top of the bell. Way back in 2008 I tried to find out what the upper limit of that top gap would be. I ended with a distance of 4.5 feet and the thing (a modified J-tube) kept working without as much as a hiccup. The ceiling of my workshop appeared to be the limit here. So no worries here, I'd say.

I'm assuming you are talking about a batchbox rocket, these are very picky about a top gap that's too cramped. In practise, a distance equal to the diameter of the riser is regarded as a safe enough limit.

But then, why building an oven in the top of the bell, not very practical in my view. And having the firebox in the basement isn't very good for heating the living room/kitchen area.

May I suggest you build the whole thing on the first floor, the firebox' floor raised to about 2 feet above the room's floor and the white oven directly on top of the firebox?
Advantages would be all the heating is in the living quarters, one is able to keep an eye on the heater and the floor of the oven will be pretty hot. Not only that, by raising the firebox in the bell the oven will be in the upper half of the bell as well. With a carefully placement of the firebox, riser and oven combo the (recommended) top gap of the riser would be flush with the top of the white oven. Probably you need to build a foundation in the cellar though, to support the heater above it.

My two cents, helped by meddling with these heaters for many years.

Peter - thank you so much. The devil (as always) in in the details.  I've considered using Matt's Continental Cookstove to keep the top of the unit at a level my (rather short) wife could reach, so I'm trying to stay with about a three foot high surface in the kitchen.  And the space is limited, so the footprint is important.  The heat leak in the cellar (with plenty of unused space) is of little concern - 13" thick ICF, double glazed, well sealed windows and the floor above is just pine boards.  I suspect it'll be a  bit like radiant floor heating in practice.  And the place is three seasons only with lowest occupied temps in the mid 40s (F).

The foundation for the chimney, and where the base of the heater will reside, sits on a little bit of crushed rock, and that is atop solid granite ledge.  The hope is to keep the wood mess in the lower level and enjoy the heat above! As for the oven in the top of the bell - what disadvantages?  I think the small bench in the second bell should provide plenty of heat in the living area and the oven will be hot enough to do any baking we wish - or is it too hot in the upper regions?

Why do I always find more questions AFTER I thought I got all the answers I needed?

Thanks,
r

Randy Butler wrote:Peter - thank you so much. The devil (as always) in in the details.  I've considered using Matt's Continental Cookstove to keep the top of the unit at a level my (rather short) wife could reach, so I'm trying to stay with about a three foot high surface in the kitchen.  And the space is limited, so the footprint is important.  The heat leak in the cellar (with plenty of unused space) is of little concern - 13" thick ICF, double glazed, well sealed windows and the floor above is just pine boards.  I suspect it'll be a  bit like radiant floor heating in practice.  And the place is three seasons only with lowest occupied temps in the mid 40s (F).

The foundation for the chimney, and where the base of the heater will reside, sits on a little bit of crushed rock, and that is atop solid granite ledge.  The hope is to keep the wood mess in the lower level and enjoy the heat above! As for the oven in the top of the bell - what disadvantages?  I think the small bench in the second bell should provide plenty of heat in the living area and the oven will be hot enough to do any baking we wish - or is it too hot in the upper regions?

Why do I always find more questions AFTER I thought I got all the answers I needed?

Thanks,
r

Hey Randy,

Everyone needs to build a stove that specifically fits their needs and environment. That goes without saying, but Peter’s advice on being able to “keep an eye on the fire” is extremely important in this situation. You need to know if somethings going wrong well before your first floor is in golfed in flames.

Maybe it’s just me, but I don’t think I could sit upstairs and not constantly be wondering what’s happening in the firebox that I can’t see.

Just two cent from someone who’s constantly watching his fire.

Fire’s your friend until it’s not.🔥

Best of luck…

Another Peter🥷🏿

Good Morning Peter S.

I am very accustomed to burning wood both in fireplaces and woodstoves at the camp over the years.  With appropriate screens in place, I never thought twice about leaving the house unattended with the fire going for a few hours at a time.  Your caution of needing to know the fire status on what sounds like a constant basis concerns me.  Does a BBH require that kind of tending?  If so, I will need to re-evaluate my heat source.
Thanks,
r

Randy Butler wrote:Good Morning Peter S.

I am very accustomed to burning wood both in fireplaces and woodstoves at the camp over the years.  With appropriate screens in place, I never thought twice about leaving the house unattended with the fire going for a few hours at a time.  Your caution of needing to know the fire status on what sounds like a constant basis concerns me.  Does a BBH require that kind of tending?  If so, I will need to re-evaluate my heat source.
Thanks,
r

I’m running a J-tube and I do use a screen, but fire is fire and I’m always cautious I guess. Probably best if you listen to someone with more Batchbox experience.

Again, in the end, it’s all what you feel comfortable with.

Best, Peter

Hi Randy,
I’ve ran a batch box for several years and had no concerns about leaving the house for several hours at a time with it running full tilt.  As with any wood-burning appliance, as long as you  build it with proper clearances, non-combustible‘s close by and mindful of its operation it will be as safe as any box stove.