Image Credit: Martin Holladay
More Musings of an Energy Nerd
For thousands of years, the chimney has been closely associated with our concept of home. Upon spying smoke curling from a distant chimney, the weary traveler ends his journey with lightened steps.
When I built my house in Vermont, as a much younger man than I am today, I designed a house with two chimneys. The house has a cellar, first floor, second floor, and attic; because I wanted the chimneys to rise five feet above the ridge, they had to be 40 feet tall.
Since I couldn’t afford bricks in those days, I spent a lot of time gathering, sorting, and cleaning stones. Three years later, when the two 40-foot stone chimneys were finally complete, my financial situation had improved, so I flashed the chimney penetrations with copper and lead. Each chimney has a copper cricket.
I love my chimneys. Like travelers of old, I love to see a wisp of smoke rising from my chimney-top as I trudge homeward. Much as I love this image, however, I fear that the days of the residential chimney are numbered.
An escape hole for conditioned air
Whether serving a fireplace, wood stove, furnace, boiler, or water heater, a traditional chimney can be problematic. What’s wrong with chimneys?
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22 Comments
Hey! I got a poem like that...
...only different.
I wrote it on a time card once when I was framing houses in Missoula, MT. We'd been running soffit, fascia, and exterior trim on custom homes where the soffit was angled back up the rafters. Inside corners were a challenge for a couple of lumps like us.
_Me and Jim we hung soffit
It weren't for fun, but for profit
We tried and we tried for compound 45s
But in the end we still had to caulk it._
Whadaya think?
I like it
But keep your day job.
Farewell Chimney
We are in the midst of replacing the roof on a 3-unit apartment house (built in 1854) and discovered that the chimney is in need of significant repair. We are also replacing our antiquated heating system with an efficient unit that will be vented out the side of the building. The timing is good, in fact, because the money we would have spent on repairing the chimney and flashing can be applied to the new heating system instead. The chimney will be removed to below the attic floor, allowing us to completely seal off the chase and insulate better, closing off a rather large source of heat loss. The mice in the attic will be cold now but the tenants will be much happier. And, having no chimney will mean less conditioned air going up and out the flue. One less beautiful brick chimney to admire from the outside, however. Will this mean folks will someday build replicas for aesthetic purposes as they've done with cupolas?
Or shutters
Interesting prediction about future fake chimneys. I'm always amazed that the designers of fake shutters always size them wrong -- forgetting that functional shutters have to be wide enough to meet in the middle of the window when closed.
No Place for a Fireplace in a Passive House
We're running into a related issue on a Passive House we're working on near Mt. Rainier. Our clients would love to have a tulikivi, but I'm certain once fired up it would overheat the house! (Not to mention be impossible to adequately seal the flue to meet air tightness requirements.) I must admit I have mixed feelings about the loss of a hearth in the home. I hope, with some practice, we can regain the poetic in these new houses, perhaps in different ways.
A way to console your clients
Just remind your clients that by omitting the Tulikivi, they just saved $20,000. Not to mention the fossil fuel that would otherwise be required to bring several hundred pounds of soapstone from Finland to the Pacific Northwest.
Put them on the porch
Fireplaces no longer belong in homes. The ones that are the healthiest and most efficient have permanent glass doors. Kind of like watching a movie of a fire. Just put them outside on screened or open porches, on patios, anyplace you don't condition the air. They make a crisp night extra pleasant.
Some things have to stay.
Like masonry chimneys. At least on the country type houses I love to look at.
The last house we (re)built we moved the block/stone chimney to an interior wall which isolated the shell penetrations to the roof and the floor. Next house will have a conditioned crawl space leaving just the roof penetration to deal with.
I don't know about air change requirements for passive houses, but I am convinced I can do an effective job stopping uncontrolled air movement through the roof plane, even on a cathedral ceiling.
Long live one of the iconic elements of a house in the woods - the masonry chimney (just wish there were a way to burn clean and still see that trail of smoke).
Stopping air movement
Jim,
Stopping air movement through the crack between the roof framing and a masonry chimney isn't too hard -- the usual method involves metal flashing sealed with high-temperature silicone caulk. The hard part is preventing unintended exfiltration up the flue.
The largest air flows up flues probably occur in wood fireplaces, followed by chimneys serving wood stoves. But there is also unintended airflow up chimneys serving atmospherically vented water heaters, boilers, and furnaces.
Controlling air movement (sort of)
What about a chimney that serves an air tight wood stove that gets it's combustion air from outside the envelope? That seems like it could work.
Clean-out door
Jim,
When a woodstove has a conventional masonry chimney, there are several air leakage points that allow air to enter the flue. These include:
1. Around the edges of the cast-iron clean-out door at the bottom of the flue in the basement.
2. Between the chimney thimble and the stovepipe.
3. Cracks between stovepipe sections, or between segments of stovepipe elbows.
"Free" passive ventilation system
A woodstove, when it's running, and the natural chimney draft when it's not, offer a no-energy exhaust ventilation system. If coupled with passive make-up air inlets and a tight envelope, this is the simplest system for a minimal constant air exchange.
Air leakage up chimneys
Robert,
Your point is well taken. In another blog (https://www.greenbuildingadvisor.com/blogs/dept/musings/designing-good-ventilation-system), I wrote, "One reason why homes without mechanical ventilation systems work better than expected is that many common household appliances act just like exhaust-only ventilation systems. Such appliances include ... wood stoves (30 to 50 cfm)."
Older homes with masonry chimneys, including mine, have more air exchange than modern tight homes. Such homes are not unhealthy -- if anything, they often provide too much (rather than not enough) fresh air.
The main disadvantage of depending on leaks (for example, leaks up a chimney) or combustion appliances (like wood stoves) for ventilation is that they don't provide dependable levels of air exchange. When the weather is cold or windy, air exchange levels are high. When the weather is mild and the air is still, air exchange levels are much lower.
Whenever air exchange rates are excessive — which they will sometimes be in homes with masonry chimneys — the homeowners will of course be burdened with the energy penalty that comes with high air exchange rates.
suspended chimney
Martin, thanks for the article and poem here. I think I may have suspended chimneys and I wonder if I can remove them safely.
The house was built in 1910 and has a much newer external chimney for the gas furnace. The two original chimneys can be seen in the attic (removed to below roof level) and there are chimney shaped columns running up through two bedrooms on the second floor. When I peer down the flue from the attic, I can see well into the second floor, but I find no traces of either chimney on the first floor or in the basement.
Can I continue what someone started long ago and remove brick by brick? From what I can tell in the attic, the chimney is free standing. On what I don't know.
I'd like to remove both the chimney and the plaster columns to add more room in the second floor bedrooms.
Anything I should consider?
Removing a chimney
Sam,
Yes, you can certainly remove a chimney, brick by brick. There is only one hard-and-fast rule: start at the top.
Thanks
Thanks, Martin.
Direct Vent
So are we saying that a direct vent fireplace in a house is not a good thing in terms of energy efficiency? I can understand not having an open masonry fireplace, but how about a direct vent gas version like those from Heatilator or Heat & Glo?
Response to MIlan
MIlan,
As I wrote in the article, "Experts now advise builders to choose sealed-combustion appliances." A direct-vent fireplace is obviously a much better appliance than an unvented fireplace.
However, gas fireplaces are not that efficient. If efficiency is your goal, you'll be better off with a sealed-combustion gas furnace than a gas fireplace.
Interior chimney?
I really like wood stoves, and have one in my moderately insulated home. I do question the idea of having wood stoves/fireplaces in efficient houses though. Our 'air-tight' (triple wall chimney with dedicated intake) certainly is far from being air-tight (put your hand in front of damper and feel the air pouring through... and when the chimney was installed, code required that no insulation be within 2" of the chimney where it passed through the wall. So, not only does does air flow into/out of the house when the stove is not in use (even with the 50 cent damper on the intake closed), but also we've got a poorly insulated chimney (at least compared to the walls) running through the interior of the house. The only way I can see installing a fireplace in my next house is to encase the chimney into a very well insulated chase (ie, it becomes exterior space). Can anyone speak to products/installation techniques which are more inline with efficient house design?
Response to Nick
Nick,
Q. "Can anyone speak to products/installation techniques which are more inline with efficient house design?"
A. Most new houses aiming for high levels of efficiency pay close attention to air sealing and thermal bridging. Masonry chimneys are a poor match for a superinsulated house. If the house needs a wood stove, it's probably best to use a modern metal chimney, not a masonry chimney.
If you just want to keep the house warm, other types of heating devices -- for example, a ductless minisplit air-source heat pump, or a sealed-combustion condensing gas furnace -- will work very well, without some of the problems that arise from venting a wood stove.
Are there any products that
Are there any products that can be recommended to simulate the look of a chimney? Something that you could stick on the ridge of a 2-story roof that, from the ground, wouldn't be obvious that it was fake?
Response to Clay Whitenack
Clay,
Places like Disneyland hire artists who perform such fakery every day of the week.
I suppose you could build a wooden chase and glue thin brick tiles on the exterior of the wooden chase -- but be very careful of asking a builder to do that, because 95% of the time the fake chimney will look exactly like what it is: a fake chimney.
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