I recently saw a “MythBusters” show, where they proved that a fire in a fireplace actually pulls heat from the house. Is this effect dramatically lessened by an air supply duct as my fireplace has?, If so why is this not a UBC or IBC requirement?. Furthermore, why would anyone in their right mind fill their chimney cavity by sweeping ashes into a cleanout?
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
This deconstruction program leader oversees the collection and reuse of a variety of products and materials.
Featured Video
How to Install Cable Rail Around Wood-Post CornersHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Yes it is true. An open FP makes a better air conditioner than a heat source. That is why sotves were developed. Not sure what you mean about the latter. The purpose of a cleanout is to sweep ashes down to an easier location to remove without scattering them all over the house.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
open FP makes a better air conditioner than a heat source
by golly, will have to try that next summer to see if it cools the house!!! NOT.
Junky:
If you're near the fire while its burning (as one poster mentioned or in a msall cabin and you keepe the fire burning fulltime at about 20% efficiency of heat transfer, then you will get heat from it. But we don't do that now since we all don't own 180 acres of woodland and farm with 10-12 kids to work it.
When we let that fire die out at night, we can't close the damper due the end of fire and ember stage. Then the heat loss (warm house air) up the hot chimney by convection is large. At this point and 'til morning when you shut the damper, the chimney's sucking heat out of the house and the event from beginning to end has become a large energy loser.
Just sit back near the wall furthest from the fire where the radiant heat is not hitting you and the air leaking in to feed the fire is drafting across you!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
by golly, will have to try that next summer to see if it cools the house!!! NOT
I watched a show once where they showed the earliest air conditoner/fan, house was built sometime around 1800.
This house was built somewhere down south, had a large foyer area, domed at the top, probably 30' up. Around the top there was a ring of gas valves. the dome could open up and when the gas lines were lit just as a fireplace, the hot air would pull the air up.
I guess you'd open the windows up and light the gas ring, then the air would pull through the house, you could control it by the size of the flame.
I don't know if it worked all that well but certainly the flame was so high up that it wouldn't add any heat to the house and pulling the air through the place had to be better then anything else they had at the time!
Doug
I don't remember the details but there were ventilation systems which used fire to move air.It was in the about 200 years ago that some high end mansions had central stairways or internal spaces set up as open air chimneys. These had small gas lights set up around the perimeter. On hot nights the gas lights were turned on and lit. Their heat causing a great volume of air to rise and exit out vents. Which caused cool night air to be sucked into the building. Often by way of double hung windows with the lower half open.In more arid regions it might suck air in through a swamp cooler. Further cooling it.
The design of the fireplace is a critical element here also, although..................... you will never gain heat, ie, add heat to your house with a fireplace, no matter what design. Excluding those with built in water pipes, yada yada yada.We're talking standard fireplaces here.A Rumford fireplace will radiate more heat out into the room because of it's design. I have one with a standing grill in front of it. With the fire going, if I take the grill away, I can immediately feel even more heat radiating out into the room.http://www.rumford.comBut, for safety's sake, my wife likes the grill in place...........popping sparks, etc.I don't care for the fresh air supply idea. No one makes a decent looking one that I know of, and if you can't regulate the air flow, you essentially end up with a blast furnace in your fireplace, ........when it's not downdrating and blowing ashes all over the livingroom carpet!There are tip & slide dampers available that can be closed when you go to bed, and a slide grill left open to exhaust. It minimizes to a degree heat loss, but that being said............the house is still cooler in the morning, and the furnace has been working overtime.But.................it sure was nice to cozy up to the wife in front of the fire last night!Now.............where'd I put that bearskin rug? Rod
Come on 4, 67368.12, I already mentioned that house!!! <G>
I know that I didnt describe it very well but it sounds like the same place your talking about.
Doug
Sorry, missed your description. That sounds very much like what I was remembering. Round room with gas jets. Like you I can't remember where it was.
Yes your supply duct helps
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
In scientific fact, with an open burn the supply duct helps a bit on some days when the wind conditions are right or still. Last night I posted some real life "flow reversal in the supply lines" in the "mechanical room in basement" thread.
A heated fireplace chimney can draw up to 3-400 cfm from the house but this does not create a negative pressure in an older, leakier house that would draw near enough air in the supply vent to fully replace the large volume going up the chimney.The weak forces in play here may only pull 30-40 cfm at best through a 6" diameter supply pipe.
We all know this 6" pipe as the most common in most residential forced air systems and that a lot of air comes out of it. It is usually designed to carry 100-110 cfm........ but to do this, it's powered by a 1/2 HP motor and blower!!! With the weaker forces of nature sucking the outside air into the fireplace, it's better to leave the supply duct out than to try and get a few cfm to the fireplace. A closed glass door fireplace may get a lot more air in but then where is the bulk of the heat going and what's the point of the fire?
One of the attempts to offset the fire place and still keep it was the heatlator /glass doors with air vents in the bottm threshold jamb. Once the fire was started good and shut down the surround heatalator would circulate air as you mention with two fans in the bottom return air openings. Back in its hay day, it was a welcomed change to an open fireplace and sexier than a stove .
I always smile when I think about it .
Stove manufactors fought backwith the insert and from the peoples want for a sexy fire added glass doors and windows in some bigger units . The nicer stoves followed with all the brass trim and glass . Even the feet on some stoves are sexy.
A little later they reinvented gas logs which were always a health hazard. in open areas. They put the things in air tight stoves vented and in inserts. So we might say the stove market won, but not like Custers last stand .
Still fireplaces come in zero clearance modes and are added in nice rental property and condos. Mostly starter stuff .
Still people continue to stuff those fireplaces with inserts after theyve spent some time being a wood slave to those open fire places. My Brother heated his home two winters years ago strickly with wood in an open fireplace . Him and his family loaded a 3/4 ton long bed pick up EVERY Sunday. I would call that load two firewood ricks measuring 4x16 face stacked x2 ft depth. Or a cord of fire wood. In my large insert that same amount of wood will go for two months of cold weather buring full time more or less. And it will heat the house.
Funny thing though about this house which makes me smile again. This house was 15 yrs old when I bought it . My Father and I built it for him personally. He lived in it for a couple of years and sold it to the owner I traded houses . When I bought it it had two openfire places still. I was the one that stuck the insert in the living room. Theres another in the den thats open with gas logs sitting in it behind an iron screen that doesnt get used. Nights that we have held Christmas parties in the winter we have used it and opened the damper a little which does nothing except make a look alike fire . Funny. They are near useless with out an insert other than a gathering point.
From being on this forum we have realized that still the education from fireplace savy doesnt have a blanket knowledge to the public.
Tim
I lived in a rental house years ago that sported a nice fireplace in the living room. I was single with a thin bank account, so I used the fireplace for heat rather than the oil furnace.
Then we had a cold snap (cold for Eugene, OR. anyway) with temps hovering around zero. When the fireplace was lit off and all cozy and romantic looking, I started feeling really cold unless I was right next to the fire, and then observed that the windows (all woodframed single glazed) had actually begun to frost up on the inside.
A fireplace consumes 200-600 cubic feet of air per minute, even more if you have a "white man fire" blazing in a large fireplace. All that air gets pulled from the inside of your home and up and out the chimney--the laws of physics are such that all that air being sucked out your fireplace must be replaced by an equal volume of air.
Needless to say, the only place that replacement air can come from is outside the home, so it gets pulled in through paths of least resistance (around doors, windows, other leaks in the home's envelope).
I've read that a typical 1,800 square-foot home has about 14,000 cubic feet of air. So if you're sending 600 cubic feet of air up the chimney every minute, it only takes about half an hour to use up all the air in the house. I'm sure a duct supplying combustion air from the outside helps (I have one for my stove), but still. . .
When my wife and I were initially planning our new house, I had grand visions of a stone fireplace in the center of the living area. Since our main design objective was energy efficiency, I dropped that scheme right quick!
View Image
Creative Communications | Logos | Business Cards | Websites | http://www.hwaters.com
So, for thousands of years people had fires in teepees and in fireplaces so they could be colder.
Give me a break people with this 'mythbuster' BS.
I spent a few weekends at -5 to -15 F in a non-insulated cabin with a simple stone fireplace - heck of a lot better that out in the cold.
Now , if you want to caveat your remarks with "when the house is overheated by a gas burner to 75 F, .... etc., maybe.
I know what you're saying, I've cozied up to many a hearth on a cold winter's night and loved the warmth radiating from the fire and masonry.But tell you what. . .let's take 2 identical houses, both with gas furnaces, but one with a fireplace (with all the wood you can burn) and one without. Say they're both kept at 65 degrees during the day and 55 at night. Which heating bill would you rather pay?
View Image
Creative Communications | Logos | Business Cards | Websites | http://www.hwaters.com
OK, admit to being a little cantakerous just to see the responses.
BTW, heated with just wood in a fireplace in a 5300 sq ft house for near 30 years (DW requested I install a HP as when she hit 60 she said she was getting to tired or old to cut split 10 cords a year).... "Fireplace' has steel doors, 98% closed damper, water wall pipes and HE in forced air ducts, , etc.... Electric bill comparisons now to then indicate "FP" was running about 76% efficient LHV of the wood used.
Gave the response as I did since nobody prefaced their remarks as applying only to full open draft fireplaces in winter , with fire out, etc........Heck, do you leave the front door open all day................ .
'Heck, do you leave the front door open all day................ .'
Not hardly.
:)
"Citius, Altius, Fortius"
That describes a wood heater much better than an open fireplace. comparing apples and pineapples ain't quite accurate. it's cantenkurate;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Megun, in your senerio are you runing the furnace at all while the fire is burning?
If so, the gas alone will be cheaper. LOL!
A masonry heater heats, looks good, uses very little wood, and yet most people have never heard of them.
http://www.mha-net.org
Treat every person you meet like you will know them the rest of your life - you just might!
aka Russian fireplace.
'Nemo me impune lacesset'No one will provoke me with impunity
junkhound, take a stress pill.
A teepee? Well it does not take a scientist to know that you are warmer sitting by an open fire in the great outdoors, no tent, no nothing, than with no fire. DUH.
A teepee? Better still. The skin or tent shell holds a bit of heat in there. Sure you can bring the temp up from the outside temp of 30 degrees. Can you get a tent up to 70 degrees like your house? Maybe if it is a relatively small tent. Even a 12 by 20 elk hunting tent can be pretty comfortable. A 60 by 30 foot tent? No way. Likewise, you might heat your 12 by 20 livingroom with a fireplace, by not the entire 30 by 60 foot envolop of the house. You get raditate heat in the tent or livingroom, but the combustion air is coming in fast. In a tent it is outside air and your stove (note stove) heats it up. In your house that air comes from teh kitchen, the den, the bedroom, all air heated BY YOUR FURNACE!
I have a fireplace. I used a stop watch one night. The furnace cycled on once each 11 minutes. I started a fire in teh fireplace, the furnace came on almost immediately and cycled on very four minutes after that.
It is not rocket science here.
Sure build a 2000 sq colonial, heat it with wood, like my grandfather. Oh, did I say he have eight stoves? One in each major room. I am sure he kept the house at 50 degrees adn fed those fires like a full time job.
Huh???
junkhound, take a stress pill.
Me stressed? What is your point, I really do not understand how anybody would think anybody got stressed over any of this?
Myths run both ways.
Whoops, forgot
Merry Christmas each and everyone!
Edited 12/21/2005 10:30 pm ET by junkhound
he musta been stirred:o)
be not a creature was stirring
'Nemo me impune lacesset'No one will provoke me with impunity
I don't know if it is true or not. Think it probably is. Junkhound makes a good point though - prior to central heating systems, fireplaces were pretty much required... I guess wood-stoves were more popular, but not sure about their history. Maybe a caveat to the "fireplaces waste heat" statement is that it is true when modern heating systems are not installed.
I guess the cast metal front cover on fireplaces was the forerunner to the wood stove? Also, maybe Clay wood stoves pre-dated metal woodstoves?
I used to sell firewood and heat with wood. Got tired of the mess/hassle/hard labor of the heat part and never could make much money selling it. Wrecked my right elbow too from swinging a maul - maybe my technique was wrong - don't know, but I still have the hammer elbow to remind me.
You can make a typical fireplace more efficient by doing a few modifications, some mentioned already (assuming it is used for occaisonal ambience):fresh air supply form the exterior to the firebox. airtight damperairtight glass doorsmotorized heaating grate (sometimes combined with doors)that draw cold room air in and blows out heated airrun the furnace on fan only (no heat) at least in the zone where the fireplace is in
If you want wood heat, don't even consider a regular masonry fireplace or modifications thereof. Install an EPA certified insert or heartmount stove. Plain and simple!!!
"run the furnace on fan only (no heat) at least in the zone where the fireplace is in"Would that actually help? What about putting an air return for the hvac directly above the fireplace? Then could turning the fan on help suck the hot air into the room? And maybe even distribute it throughout the house?
The theory is that at least it won't suck out the heated air, assuming a FAI is in place. But if the convection is great, and the house is leaky the FAI may not supply enough air versus what is being displaced, so the house will still get colder and eventually require the heat source to generate new heat.
Don't forget that prior to central heat, the fireplace was also the cook stove! So it served more purposes than just heating the air in the cabin.
If so why is this not a UBC or IBC requirement?
Well, because FP are "expected" features by house "customers." In days of old (existing construction, which the codes have to at least consider), infiltration meant that houses were drafty, and "self made" the make up air to send out of the chmney.
The Codes are also more about building houses to a minimum standard overall. They, generally, do not address "pure" energy efficiency issues. Otherwise, no chimney mass would ever be permittted in (through) and outside wall in cold climates.
Furthermore, why would anyone in their right mind fill their chimney cavity by sweeping ashes into a cleanout?
Well, the clean-out is "supposed" to have either an exterior access, or a trap-type termination in a non-living space (like a basement or cellar) so that the ashes can be removed without tracking them across the LR rug.
Also, while some ash bed is "good" (tempering the heat upon the brick hearth & catching coals and embers), it also has to be low enough under the log grate to allow good air circulation. So, you have to be able to remove ashes somehow.
I did not see the episode, but this is not the first study to conclude the same. One I read years back estimated a 25% net heat loss for daily evening use.
The old colonial fireplace design when in constant use may have provided net warmth (though not efficiently), but for occasional use it is a loser because you cannot close the damper until the smoldering ends. 12 hours of smoldering amounts to a lot of convective losses up the chimbley.
Also, the colonial design called for serious thermal mass and central location, so radiant gains would continue even as the fire died down and convective losses accelerated.
Modern interpretations have less mass, and it is often on an outside wall.
Here is an interesting article on this topic:
Excerpt: "The best efficiency a conventional fireplace can have is only 15%"
And by this they mean operating efficiency!
http://hearth.com/what/more/skip.html
fireplace air conditioner.
place ammonia box in the fireplace in the summer for AC, no more kerosene heater needed. <G>
View Image
Edited 12/21/2005 12:31 pm ET by junkhound
I figure that if one were to sweep ashes into the " Cleanout " in his new house, It would probably take several years for the ash to start accumulating at the "cleanout" door in the basement. Until that time, the ash would be filling up the cinderblocks of the chimney, absorbing moisture from the concrete, and if dry, would become airborne through any drafts passing through the cleanout from convection or some other air transfer. Perhaps, though physically exhausting and time consuming, One would be best served by scooping the ash out of the fireplace, or hiring an undocumented individual to do it for them.
" Until that time, the ash would be filling up the cinderblocks of the chimney,"Say what????A cleanout is a chute built from the grate to the cleanout door a short distance below the hearth. There would be no way for it to let ash get into the cinderblocks. It goes right to the back of the cleanout door, where a shovel is used to remove the aash into a bucket. Four or five cords of wood would make more than enough ash to completely fill any cleanout chute I have ever seen.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I saw the same eposode also and it is true. I read a artical on web site that said if you have a tight house that you would need to crack a window so it would draw, and in order for the somke to draw out the flue you have to have some kind of air draw from windows, doors or a drafty house.