Demo exterior fireplace or outsulate it for energy efficiency?
New member of GBA — I’ve been reading it for some weeks. Lots of great material and excellent discussion!
We’re doing a remodel and — if not deep, then at least shallow — energy retrofit of our 1.5 story 1917 house near Seattle, including re-siding and 1.5 ” of outsulation (mineral/fiber or fiberglass board), air sealing, and attic insulation, including kneewalls adjoining living spaces. Part of this project involves our exterior brick fireplace. We don’t use it, and have been considering demolishing it — not just because of the heat loss through the flu, but also because of the convective heat loss through the granite on the inside out into the air. (I’m not an engineer or architect or carpenter, but a layperson who’s been trying to educate himself about energy issues, so I may not be using my terms correctly) We would replace the fireplace with a free-standing wood stove or pellet stove, as backup to a multisplit (existing heating is 90 year old oil furnace). The free space on the South wall might be used for solar thermal.
One alternative is to insulate over the outside of the chimney, and then put a woodstove insert in the fireplace opening. The third alternative is to try to air seal around the fireplace, put an insert in it (wood or pellet) and leave things as they are otherwise.
My question: is it worth the (considerable) expense to pursue options a) or b) purely due to energy concerns? Or is the actual energy loss. not worth the great expense?
I realize there’s a subjective dimension to this question, but I’m interested in whether the energy consultants I read here (both in blogs and in comments) would find either the chimney demo or outsulation strategy excessive for people of not-unlimited means — i.e. better simply to spend the money on more insulation elsewhere (for example, the basement) and accept the limitations of the house.
Thanks for any help!
Art Strum
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Replies
If you end up not demoing the brick fireplace + chimney at a minimum you should verify that you have a Chim-a-lator or similar gasketed damper mechanism that seals air bypass which will be the largest method of heat loss.
If you are completely residing and outsulating your entire house you are already taking about a lot of money. If you are hiring a contractor I would advise you to have them bid on demoing the chimney. It might not be a large expense in the scene of the project and it would help to clearly establish your thermal envelope and a continuous air barrier.
If you have walls that are well insulated and a bare masonry chimney that acts as a large thermal bridge it will likely be a source of discomfort when occupying that room. Since the square footage of the chimney/fireplace is small comparing to your ceiling area or basement outsulating around the chimney may have less of an impact on cutting your energy bills.
It will be easier to make decisions among different energy conservation measures once you have someone put a price to them. Be considerate also of all the implications of changing or demoing something in a retrofit. Demoing the chimney will cause work to the roof. Outsulating the walls you will need to increase the depth of your window sills.
I'm a designer and don't do bids but the scope you describe could run you anywhere from $50K to $100K+.
Art,
You're in a relatively mild climate zone and it sounds as if the chimney is on the south side. I don't think you get a lot of winter sun in Seattle, but the chimney could be functioning somewhat as a high mass solar collector, though now the heat would be largely convected up the flue.
If you have an interest in a woodstove (I would avoid pellet stoves since they require electricity and a non-electric woodstove serves as backup when the power is down), it may be less money to install an efficient insert (check out Lopi) than to demolish the chimney and repair the roof. Make sure the chimney has a clay flue or install a stainless steel flue liner, and look into a gasketed chimney cap (like the SealTight).
Insulating the outside of the chimney, even if it requires boxing in, would significantly reduce conductive heat loss, particularly when its in use. Make sure to maintain a 2" separation to all combustible framing and do any necessary repointing of the brick before burying it.
Thanks very much J and Robert. (Robert, I've read about your work on Builditsolar.org) J: I have a carpenter/friend doing the outsulating of the walls, and I do have bids (not from him) for the demo of the chimney. It's about 1/5 of the cost of the entire siding/outsulating project (we're not doing the roof at this time). Plus, if we add a wood stove (Robert, good point about the pellet stove), then besides the cost of the stove we would have to add the installation of the stovepipe, and a hearthpad, as well as repair work to the wall and the roof.
My carpenter friend estimates the cost of outsulating the chimney (mineral board, encapsulated with masonry) at 4000 -- just about the same as just the demo work. (but he wasn't sure, since he wouldn't do the masonry work himself) I think it could be done more cheaply, but our carpenter insists, perhaps rightly, on preserving the look of the house with exterior masonry.
It sounds like maybe the thing to do, if I can get a better cost estimate, is to outsulate the chimney. The brick is actually in excellent condition -- needs no repointing. Robert: in order to reduce convective heat loss, the whole length of the chimney would need to be boxed in -- is that right? (that is: not just the portion on the exterior wall of the house)
Thanks again for the contributions - I've looked and looked but not seen much if any discussion anywhere about outsulating chimneys.
Art
If you are serious about energy efficiency I would argue that in the process of replacing your 90 year old furnace you would install a heating system in which a wood stove as a backup would only be a luxury - and one that only adds to your energy consumption. If demo of the chimney is similar in cost to insulating it my vote is to demo it have a better defined thermal and air envelope and leverage the south elevation for additional passive solar gains.
I respect retaining the exterior look of attractive older homes which I feel is a public amenity but when it comes to exterior chimneys in heating climates (remnants of past energy inefficient building practices) I think in most cases you can do without them.
This will be a recurring issue for energy retrofits. Thanks for the post.
J:
Thanks for the follow-up. The wood stove would, as you suggest, only be a backup and occasional luxury. We've considered, over a long period of time, staple-up radiant with an inverter compressor air to water heat pump (extremely expensive), more recently, inverter compressor mini-splits - now I'm considering a newer inverter compressor heat pump with air handler to use existing ductwork. And I like the way you put it -- exterior chimneys are historical remnants which can be done without. That was exactly our thinking in considering demolishing it -- along with making space for solar air panels or solar thermal or the like. But I'd like a backup to electricity, wood stoves allow what Alex Ross on GBA calls "passive survivability," and the expense of demo'ing plus new installation, plus finding a suitable space has us looking again at our existing fireplace and wondering if it doesn't make sense to refunction it.
In any case, the feedback is very helpful in thinking through this problem.
Art
We've had some crazy weather this year in Minnesota. Today there are wind gusts up to 60mph and many in the cities are without electricity. Climatologists have predicted more severe weather events due to climate change. I'll have to check if my natural gas boiler can run without its electronics. Probably not.
Can't argue with you on having a backup. Good point and I'll keep this in mind for future projects.
Arthur,
It may make the most sense to get rid of the chimney, improve the thermal and air barriers and then - if you still choose - install a free-standing woodstove with metalbestos or triple-wall SS chimney (which could be done at a later date).
Oh, and don't forget to either sell or repurpose the used bricks or have a non-profit building materials re-use organization come do the demo in return for the materials.
Hello -
I have a related question regarding new construction. We are working on an ICF house with a CMU fireplace and chimney. I have proposed rigid insulation on the exterior of the chimney but the contractor is concerned that this would be a code violation. Can anyone advise if this is the case? or if we need an airspace between the CMU and the chimney?
Thanks,
Sara
Sara,
Is the chimney entirely inside of your home's thermal envelope (except where it pokes through the attic and roof)? Or is this an exterior chimney that has three sides exposed to the weather?
Martin, It is exposed on three sides - on an exterior wall. How do you recommend dealing with this condition? and be within code requirements for air space etc?
Thanks,