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Conduction heat loss from unused brick chimney question

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Posted by rob on December 27, 2004, 7:58 pm
Here in Atlantic Canada there are many 100+ yr old buildings with
massive brick chimneys that were part of the coal heating systems.
After converting to electric heat everyone knows that they need to be
plugged to prevent heat loss but i was wondering if it would be
worthwile to remove potion above roof.

Can anyone tell me how much heat loss a 2x4' brick chimney say
sticking up 3 feet from roof produces?


Posted by Ecnerwal on December 27, 2004, 10:50 pm
 rcam001@hotmail.com (rob) wrote:

The rumours of inexpensive electricity in Canada must be true. If it's
not being used, and won't be used, yes, definitely. Might as well rip
the whole thing out and gain some space inside the house, as well; at
minimum, rip it down below the insulated level and insulate over the top
the same as the rest of the attic/roof.

Brick/masonry is roughly R1 per foot (english R, not metric R). Whether
or not the attic is heated, the transition from warm interior (2nd floor
or warm attic) to cold (cold attic or exterior) is typically less than a
foot long. Call it a foot long - you're looking at an 8 square foot R1
hole in the insulation - rather like a single-pane window of the same
size, though probably somewhat worse (but difficult to tell excatly how
much worse). If your attic has typical Canadian R40 insulation, much of
your roof heat loss is probably via the chimney. If (as usual) there are
also air leaks associated with it, the loss could be much greater.

Say it's 32F outside and 68 F inside - the chinmey uses ~288 btu/hr, or
about 2KWh per day. At 0 F outside, ~544 btu/hr, or 4KWh per day.

Cats, Coffee, Chocolate...vices to live by

Posted by News on January 5, 2005, 4:19 pm

If the chimney breast is internal, not on an outside wall, then take it down
below the insulation level.  This will add thermal mass to the house and if
a timber framed house this will be beneficial.  Seal up the breast.  You are
supposed to leave an air brick in the fire opening to give and air flow to
prevent condensation occurring.  It may be beneficial to fill the whole
thing with sand.   I have seen some taken down below insulation level and
low temperature heating pipes inserted, which heats up the breast.  This
give a nice ewarm feel to the rooms around the breast.

If the breast is on an outside wall and external, protrudes outwards and not
into the room, then it would best to remove the breast.

If the house is old and attractive then leave the breast and seal up.
Sometimes aesthetics are worth paying a tiny fuel price for.

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