I've got this red brick fireplace taking up half a wall. Capped the chimney decades ago, but it's still siting there conducting heat outa' the place thru the bricks. How would one go about calculating the "R-value" to estimate the heat loss. Any useful rules of thumb?
Trying to decide whether to put insulation over the bricks on inside or outside or both.
On Sun, 05 Dec 2010 14:02:51 -0800, mike wrote Re What's the R-value of a fireplace?:
Brick has an R-value of 0.8 but there are other materials behind the brick. You'll have to identify them and add their R-values to the brick.
Both if you can do it.
Your local building permits office can probably advise. You must provide basic information, e.g. whether the brick wall is solid or hollow, how thick, etc. If you want the general scientific background, the US NIST can oblige (but its main interest appears to be fire avoidance rather than heating fuel conservation.)
The fire box and chimney will convect in cold, I use a piece of foamboard to seal my firebox up, mine is removable, held in place with magnetic tape and painted dark, it helps alot.
Have you talked to your tax assessor and your insurance company to see how much you'd save each year if it wasn't there. Then calculate the heat loss & how much it would cost to tear it down and put a proper wall there. If you're not using it, you can probably make better use of the wall space.
Jim
Also walk around your neighborhood, and see what percentage of the houses have fireplaces. If yours is the only one WITHOUT a fireplace, it could make it harder to sell when the time comes, for you or your heirs.
As pointed out the R value is not much. Whether you want thermal mass inside is another matter, it'll take a bit longer to heat and cool off.
You may wish to consider pouring some insulation in the chimney, a much better insulator than air. Probably would cut you cut your heat loss dramatically. Not sure what condensation issues you would have though. Either cellulose which can have some moisture content or asbestos free vermiculite, I'd think.
Google "insulate unused chimney".
Jeff
Why don't you put a good airtite insert into it and MAKE heat for free?
Oh, but we're not supposed to think about resale value, here in AHR.
The biggest heat loss I found with fireplaces is air leaks. Wind can blow right in sometimes. Create a negative house atmosphere and feel for leakage. There are always holes in the chimney. If you don't want the eye candy of the fireplace, seal it with something like rigid fiberglass, "ceiling tiles" Foam board is illegal, but you can also use polyethylene insulation sheets. which is semi fire retardant and does not need covering by drywall. For permanent seal, insulate and drywall.
R values are varied according to which chart you use. My typical cinderbock gets up to R 3.5 or more with fiberglass inside the holes.
For the most part, R value usually means inches of dry wood. 1 inch =3D R 1.
"Don Phillipson" wrote in news:idh4ct$ti7$1 @speranza.aioe.org:
I found the reference below in my files;
Concrete block (8") R-Factor Concrete block (8") 2.0 with foam insulated cores 20 with 4" on uninsulated stud wall 4.3
I very much doubt the middle value, R of 20 for just some foam in the cores seems way too high. The first and last value seem in the ballpark.
I have a second reference that shows brick ranging from 0.10 to 0.35 per inch thickness.
Seems I recall a figure of maybe adding R2-R3 for adding foam in the cores. I just started to install 1/2 inch foam to my block. This is glued and taped together to form a vapor barrier, from moisture getting in. On top of that I will install studs and fiberglass or mineral insulation, and drywall. I see the Roxul products being superior for possible damp conditions, and superior fire and acoustic control, but I'm getting off track of the OP.
Only free if you have a wood lot out back, and if your insurance company doesn't care. If you have to pay for firewood, it is almost always more expensive heat than gas.
..and if your time is free.
When I lived in Vermont I'd use wood as auxiliary heat. When it got really cold the boiler (hydronic-oil converted to gas) wouldn't keep up, even running flat out. A wood fire would make the place toasty anytime. No, it saved nothing but it was nice. I went though a cord of wood every five years. ;-)
Thanks for the inputs. I realized that I have no idea how a fireplace is constructed.
I did open up all the unheated areas and opened the heater registers. The gas consumption went up by about 20%, which sounds reasonable given the area added includes the patio door and fireplace.
I was surprised that the temperature of the bricks was the same as the adjacent wall. Measured with IR thermometer, so there may be emissivity issues not yet investigated.
The exhaust fan over my stove can pull 5 Pascals of vacuum on the house. I turned it on and went probing with my trusty incense stick. There's a small amount of air coming out of the fireplace, but it's not coming down the flue. The cap works. It's coming from the bottom near the front. Need to pull out the homebrew heat exchanger and look under there.
I've never studied that since i've never had to pay for wood. We have a lifetime supply for at least 100 people of hedge (osage orange) and the wood heat is so much more comfortable, I'd do it even if i had to pay $100 a cord, i'd still come out ahead. you just have to have a good stove.
-snip-
$225 is the going rate in this part of the world. That'll get you maple & oak if you're lucky. Hickory or osage would bring a premium.
Just wondering how you get that "free" wood to jump from the bushes into your stove- and season itself on the way.
Jim
-snip-
Now go outside when the sun is off it and measure the outside temp. The colder it is outside the better. I think you'll see your difference there.
Jim
I actually own two miles of hedge row and i can go out and cut ONLY the already dead stuff and bring home a weeks worth in about an hour. Being self employed, this task requires no special scheduling.
I understand not paying for the standing wood--- but having been there myself many years ago, I know the amount of labor and equipment that goes into gathering firewood. It is a good hobby and can be cheaper than a gym membership for cardio workouts---- but it is *far* from free.
Jim
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