Post by kita on Jan 11, 2009 12:43:37 GMT -8
Hi everyone,
Thanks for the forum and all your work!
I've got a few questions about adding a rocket stove and cob bench to an existing open fireplace. I have done a google sketch of the proportions and materials but can't work out how to upload the image to the board.
Anyway, here are the details of the existing fireplace:
-its on the ground floor, with a brick and concrete foundation.
-the front opening is about 3 1/2 foot by 2 1/2 foot. The floor area about the same.
-the floor of the fireplace is a double layer of brick, which raises it about 3 inches above ground level, also of brick. There is also a limestone apron infront of the fireplace, at the same height.
-the chimney is internal, built against an east facing exterior wall. Its pumice lined, limestone clad, about 1 ft square internal area, about 18ft long.
The rocket and bench I have in mind are from Ianto and Linda's book, based on a 55 gallon barrel heat riser, 17 gallon feed tube and 8 inch ducting. Its to heat a stone walled 250sq ft room, with some heat going to the bedroom above it. After the clean out hatch I want to run the bench in a circle out from the riser, into the room, and then back into the fireplace on the other side of the riser. Because there isn't much space between the riser and the fireplace mantle, the cob bench will stop before it, and the flue will exit the bench via double walled pipe to keep it cosy. It will then meet a T behind the riser, with the bottom end of the T for access and creosote and the top T leading to a vertical double wall pipe which mates to a flat plate blocking off the chimney to prevent CO backdraft. After that the smoke goes up the old chimney. (As usual a picture would have saved alot of words...Sorry guys)
I can only fit a 28 inch heat riser in the fireplace (3/4 of 55gal barrel). Since there will be less push in the flue, I decided on a shorter bench, only 14ft. I know this means losing more heat but anything will be an improvement on the present open fireplace which burns a tree a fortnight!
My questions are:
-do you think 14ft is long/short enough given that the smoke also has to go up an 18ft chimney?
-should I use straight pipe and elbows in the bench, or could I get away with flexiflue which will give a nice curve but the corrugated surface will increase drag? I'm wondering whether a long curve has less resistance than a series of elbows anyway. Cheaper too.
-do you think I need to reline the chimney with double walled pipe? I can't afford it but would like to know your opinion. I'm thinking just leave access to the chimney so I can inspect and sweep it out if necessary.
-Since the limestone plinth and brick floor will be acting as heat stores to some extent I'm a bit worried about the limestone cracking or moving away from the brick. More insulation under the feed tube and heat riser I guess, but it reduces the height available as I can't dig down. What 'natural' insulant has the highest U value for a given volume?
Ok thats it, thankyou for your thoughts,
felix
and let me know if I can post the pics!
Thanks for the forum and all your work!
I've got a few questions about adding a rocket stove and cob bench to an existing open fireplace. I have done a google sketch of the proportions and materials but can't work out how to upload the image to the board.
Anyway, here are the details of the existing fireplace:
-its on the ground floor, with a brick and concrete foundation.
-the front opening is about 3 1/2 foot by 2 1/2 foot. The floor area about the same.
-the floor of the fireplace is a double layer of brick, which raises it about 3 inches above ground level, also of brick. There is also a limestone apron infront of the fireplace, at the same height.
-the chimney is internal, built against an east facing exterior wall. Its pumice lined, limestone clad, about 1 ft square internal area, about 18ft long.
The rocket and bench I have in mind are from Ianto and Linda's book, based on a 55 gallon barrel heat riser, 17 gallon feed tube and 8 inch ducting. Its to heat a stone walled 250sq ft room, with some heat going to the bedroom above it. After the clean out hatch I want to run the bench in a circle out from the riser, into the room, and then back into the fireplace on the other side of the riser. Because there isn't much space between the riser and the fireplace mantle, the cob bench will stop before it, and the flue will exit the bench via double walled pipe to keep it cosy. It will then meet a T behind the riser, with the bottom end of the T for access and creosote and the top T leading to a vertical double wall pipe which mates to a flat plate blocking off the chimney to prevent CO backdraft. After that the smoke goes up the old chimney. (As usual a picture would have saved alot of words...Sorry guys)
I can only fit a 28 inch heat riser in the fireplace (3/4 of 55gal barrel). Since there will be less push in the flue, I decided on a shorter bench, only 14ft. I know this means losing more heat but anything will be an improvement on the present open fireplace which burns a tree a fortnight!
My questions are:
-do you think 14ft is long/short enough given that the smoke also has to go up an 18ft chimney?
-should I use straight pipe and elbows in the bench, or could I get away with flexiflue which will give a nice curve but the corrugated surface will increase drag? I'm wondering whether a long curve has less resistance than a series of elbows anyway. Cheaper too.
-do you think I need to reline the chimney with double walled pipe? I can't afford it but would like to know your opinion. I'm thinking just leave access to the chimney so I can inspect and sweep it out if necessary.
-Since the limestone plinth and brick floor will be acting as heat stores to some extent I'm a bit worried about the limestone cracking or moving away from the brick. More insulation under the feed tube and heat riser I guess, but it reduces the height available as I can't dig down. What 'natural' insulant has the highest U value for a given volume?
Ok thats it, thankyou for your thoughts,
felix
and let me know if I can post the pics!
