Could you elaborate a bit?
Fires need oxygen to burn. Exhaust gasses are vented up an open chimney. Make up air has to come in from some place. Sure some heat is radiated back to the room, but how can you be sure that more is radiated back than goes up the chimney? Keeping in mind that there is always an exception to any "rule", and that generalities are generally wrong, perhaps a bit of explanation would help here. Myth all the time? Some of the time? None of the time?
Testing a fireplace is relatively simple. On a cold day with the house temperature around 70, turn off your primary heating system, start your furnace, monitor the change in temperature. Limit the heating are by closing of the room(s) with the fireplace. Compare with another test with similar temperatures but don't run the fireplace.
We have a fireplace that was built with the wrong dimensions and it sucked heat out of the house. The solution was to add a glass fireplace screen. No more negative effect. Added a heat exchanger (basically a box with a fan and connecting tubes to move room air through the heated box) and efficiency was vastly increased. However the fireplace was still a poor heater compared to our wood stove.
If the house is at the same temperature as the outside, lighting lighting a fire in the fireplace will make at least that room warmer. Some heat will be radiated out the of the fireplace, and not all of the air thus heated will be ejected up the chimney.
Cold air will be sucked in from outside to replace the exhausted air, but that can't be colder than the room was to start.
If, on the other hand, the room is heated by some means other than the fire, then the amount of heat needed to heat the replacement air may exceed the amount of heat radiated into the room. This depends on the temperature of the outside air, of the pre-heated inside air, and on the design of the fireplace.
If your house is heated to the cannonical 72F, and the outside temperature is below freezing, then running an open fireplace is likely to be a net loss. Unless you've got a really big fireplace.
A glass or even wire firplace screen can be used to restrict the amount of air into the firebox to that needed to actually run the fire, but most people aren't interested in doing that much management.
of course, if you're designing your house, one of the easiest ways to fix this problem is to supply the fireplace with combustion/exhaust air from somewhere that's not in the heating envelope. I don't know if you can do anything using the ash-pit in fireplaces built with them or not.
--Goedjn
>
Not a myth at all. At least in my personal experience. I installed a Heatilator (tm) recirculating fireplace back when. On a cold, cold day I had a fire going. Thermostat was off. Kept chucking wood in and watching the thermometer. It kept going DOWN.
Fireplaces are good only for two things.
a. Romance. b. Getting rid of firewood.
They are no good at all for heat other than directly in front of them.
Harry K
Well, suppose your fireplace puts out 60,000 BTU and your house is losing 80,000 BTU.
You are using free firewood for 60 and the other 20 are being supplied by your furnace. Lets see now, you're paying for 20 instead of 80. Is that cheaper?
Depends on what your house looses when you're NOT running the fireplace. Or would loose, if you didn't have one which is likely to be even less.
In my case. by shutting down the fireplace, the furnace could keep the house warm. That was the last season I used that fireplace. Went to a stove and kept the house toasty with almost no oil at all from then on. Summary comes down to I was burning wood for a heat loss through the fireplace, i.e., efficiently getting rid of firewood.
Harry K
-snip-
The *huge* variable everyone seems to miss in these 'scientific' calculations is the efficiency with which a central heating unit distributes the heat. First off- you have a thermostat that is easily regulated - and little waste heat being created. [no 90degree rooms- night or weekday setbacks]
Secondly, if done right a central heating system heats the outside walls making the house feel comfortable at a lower temp. Not to mention zoned heat or built in humidifiers.
If wood is free- a space heater might save some on heating. They are handy to have in an emergency-- and they add to the ambiance. But if you are buying wood- forget about it.
Jim
That's true. I never thought about that.
I had an avid hunting friend years ago, that happened to mention that hunters never kill porcupines, because if someone gets in trouble in the wild, they are easy to get and could provide food in an emergency.
That's the way I've always felt about burning softwood. Why not save it for a national emergency or something? You're probably losing money by burning it anyway. On the otherhand, If you happen to already have a wood-burning stove and if you happen to have a 3/4-ton truck and if it happens to be empty and if you happen to be camped next to some good hardwood and if it happens to be free for the taking, then it probably makes a lot of sense to take it home and burn it.
That's a lot of "if's" though and I've always thought there are easier ways to save money.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.