RMH verticle flue clearance

I'm getting scary close to starting a RMH that I've been thinking about for over a year.  It's a 6" J-tube burn chamber with a 55 gallon drum bell.  I have to figure out the size of the mass bench still.  I have two location options...

Option one, in the basement along a wall with a 12x24 basement window near the hung ceiling and then 24" eves to get by to clear the roof for an exterior chimney.   I like this location best because it is in a "living space" in the basement where I can monitor the fire easily and possibly build a nice looking bench for mass.  The only cons are clearance through the old window space and increased cost for a chimney which I understand could run into the hundreds of dollars.  The cost is a factor I'm OK with to gain a living space RMH.  I don't know what to think about the clearance part of the equation.

Option two, also in the basement workshop just under an existing masonry chimney access point.  I like this location least as it is away from the "living area" and I will be stealing a substantial amount of floor space for the footprint of the RMH.  The space is already crowded with woodworking tools which I can move but makes the space, a cramped 13'x22' shop, even more cramped.  In this space there would be no use of the bench for the mass other than heat storage.  It wouldn't be a sitting area and the heat that the RMH would generate would be traveling a long distance to the living area.  Though it is right below my kitchen which would create nice warm floors like when we had a wood furnace 30 years ago.

My biggest concern about option one is clearance of the chimney through the old basement window.  Obviously the window will be removed and a frame built to accommodate the chimney.  With chimney temps in that area fairly cool will clearance be an issue?  I have no experience with RMH so I'm apprehensive about choosing this location.

Thanks for your thoughts, Tim

That is a tough one! Heat in the living space is important, but so is safety.

Is the basement window hole big enough for a proper "through the wall" chimney thimble? One of those would take care of a lot of clearance concerns... but would also run you into at least two 90 degree chimney angles which would make it harder to get a draw going. A bypass would help.

Matt Todd wrote:... but would also run you into at least two 90 degree chimney angles which would make it harder to get a draw going. A bypass would help.

Thanks Matt,

The existing chimney,  though likely the safest option also requires the two 90 degree turns and empties into a significantly larger chimney.  Do you think the larger masonry chimney would take a lot longer to create a draft seeing it is mostly outside a heated space?  I'm not sure how much a flue needs to warm up before having a good draw.  I'm assuming it just needs to be warmer than the surrounding air to start but that start of the draw could take some time.

Yes, the chimney just needs to be warmer than ambient air to start a draft... how much warmer depends on the exact conditions. Is the masonry chimney mostly exposed to the exterior air, or just not in a living space? How tall is it? What is the possibility for running a horizontal flue from a location in the living space to the chimney? Distance? Obstacles?

A 12" window opening assuming it is not plastic would be fine for an insulated chimney section to pass through. Is there a wood or plastic frame there? In that case I would remove it to the masonry opening. An insulated filler with metal skins inside and outside fastened to the masonry would work fine, though it might be frowned on by a code inspector if that is a concern. A properly built RMH will never make the chimney at the wall dangerously hot, but if someone were ever to put a wood stove in that spot, well, better safe than sorry down the line.

I think I'll go with the work shop location.  The living space/basement window location is right below a bedroom window.  Not ideal to be installing stove pipe right outside that.

The two locations are on opposite ends of my home.  And a warm kitchen floor and nearby living room floor sounds better than bedrooms being warmer than the rest of the house.  I like it cool when sleeping.

The existing chimney is mostly inside an unheated garage and next to the home wall.  That should provide some draft advantage.

Thanks for the replies.

I agree, warmth under daytime living areas sounds like a better idea than under bedrooms. If you are putting the RMH in the shop, I would advise a tall narrow masonry bell to minimize the footprint.