How much heat loss in a traditional fireplace?

[Adirondack]

I was wondering how much heat loss is lost with a fireplace. Before I bought my insert I noticed you had to get a really big fire just to produce any amount of heat for the room. Not just a small fire and it keeps the whole house warm. I would like some numbers to discuss with friends that are deciding to do the conversion to a insert. Thanks

 

[Dalmatian90]

Numbers in my head for efficiency are:

Open hearth: 10%
Non air-tight stove: 40%
Modern Insert: 60%
Air-tight stove: 80%

i.e. a fireplace provides 10% of the BTUs in the wood as heat to your room, an airtight stove delivers 80% of them.

 

[Wood Doctor]

Numbers in my head for efficiency are:

Open hearth: 10%
Non air-tight stove: 40%
Modern Insert: 60%
Air-tight stove: 80%

i.e. a fireplace provides 10% of the BTUs in the wood as heat to your room, an airtight stove delivers 80% of them.

These appear rather accurate. Good post. I have even seen less than that for an open hearth. The radiant heat eventually all goes up the chimney as the fire dies and drags whatever warm air that was generated right out of the house.

If the temperature outside is dropping rapidly, you could be in worse shape than you were before you lit the fire. Gasp!

 

[Adirondack]

Thanks

What do you mean by air tight stove?

 

[Dalmatian90]

Most things from the Fisher stoves of the 1970s on through the modern EPA approved stoves. You can close the air dampers on them and cut off their air supply completely.

Non air-tight stoves need to have a damper on the stove pipe to control the fire, because you can't completely turn off the air.

Anyway, there is some wiggle room. A Fisher style stove is in the 60-70% efficiency range, while the top of the line catalytic converter EPA approved stoves are up around 85%. The non-cat EPA stoves are in between those two.

My old fashion Boxwood is a classic non air-tight stove. The air damper only controls part of the flow. It can still draw air from a gap at the bottom of the door, and from around stove plates on the top. It needs a stove pipe damper to help control the fire. Seen pictures from of Civilian Conservation Corps barracks using stoves identical to mine.

 

[traditions]

If you are burning a fire in a open hearth, it actually pulls most of the air out of the room and up the chimney.I would think that a fireplace is the most ineficient use of wood.Even without a fire going in a fireplace it will pull heat out of a room if the damper isnt closed tight.

 

[mga]

I was wondering how much heat loss is lost with a fireplace. Before I bought my insert I noticed you had to get a really big fire just to produce any amount of heat for the room. Not just a small fire and it keeps the whole house warm. I would like some numbers to discuss with friends that are deciding to do the conversion to a insert. Thanks

depends on many variables.

1. is this an open face fireplace, stone/brick inside? or, does the fire place have convection vents, or a steel liner?

2. how well insulated or air tight is the house?

3. type of house.

my heat source is a fireplace and my house was built in 1958. i have done plenty of insulation and door/window upgrades to the house.

my fireplace has a thick steel liner with convestion vents on the sides. i also use two cabinet style glass doors that i sealed before installing them and i added rope insulation to the doors. this makes it almost like an air tight burner. my fire burns on a "heatilator" type grate that, via use of a blower, throws hot air out from under the glass doors theu a 1" opening. my home is an "L" shape ranch.

i can start a fire and withing an hour the main room is hot. the problem i always have is that it produces too much heat and we have to start fires, then let them die down to almost nothing before adding more wood. during the night, i'll add logs and by morning the house is still in the mid to upper 70's thru-out.

i wouldn't trade this set up for any other type of wood burning stove at all.

i will agree that an open faced fireplace is just like having a window open, but you can't compare the efficiency of that type to another type of wood burner.

 

[Scootermsp]

I use my fireplace on NFL Sundays when it's cold enough out. A few years ago I put a cast iron Fireback behind my andirons. The fireback radiates a lot more heat back into the room and protects the masonary at the back of the firebox.

 

[Wood Doctor]

MGA's fireplace setup (Post #3) is a far cry from the old open hearth fireplaces that many homes still have. The heatilator idea was a good one that preserved the beauty of the old open hearths and added gobs of efficiency. The sealed glass screens also knock out much of the heat loss up the chimney.

I have one of these heatilators installed in the fireplace on the main floor of the house, but LOML won't let me burn wood in it. So, I converted it to NG and it is seldom used. My Federal Airtight 288CCL is in the lower level of the house and it's rated at about 75% efficiency and 55,000 BTU/hr. That keeps the floor upstairs warm, and that's about half the battle.

 

[Geese]

MGA I would love to see a pic and details of your unit. I have a heatilator and want to improve upon it. Sealing the doors is of interest to me. I am also interested in the grate you refer to. Any internet links?

 

[mga]

MGA I would love to see a pic and details of your unit. I have a heatilator and want to improve upon it. Sealing the doors is of interest to me. I am also interested in the grate you refer to. Any internet links?

i'll get a picture of it today. my heat thing was called an Arvin Heat Stream. they no longer make that particular unit, but there are others out there similar to it.

the doors i have now are cabinet doors. i used to have those bi-fold types, but they would leak air from the glass seams...until i busted one...lol

 

[got6ponies]

close to air tight

taken w/night vision.

 

[woodbooga]

I read an 18th century diary kept by a Stratham, NH man named Samuel Lane who made entries almost daily for 60 years.

I've not seen his dwelling, but assume it probably had the standard chimney with 6 fireplaces - 3 downstairs and 3 up.

It was a common occurance for water on his washstand to freeze over night.

Even a Rumfordized hearth is going to pull a lot of heat up and outta the house.

 

[CrappieKeith]

Some fireplaces are down to 1% but if you add glass door front you can double the efficiency.

Let's get real here guys. These new EPA ratings are of the Lower Heat Method of testing(European) which says basically there's no moisutre/water in the wood. This artificialy drives up the percentage by a good 10-12%.

Take a look at gas or oil.Whenever you get to anything higher than 83% efficiency the gases being vented are so cool that they will start to condence.
High efficient gas furnaces have condensate pans with drain hoses to take away this water.
An oil flame for example is about 2000 degrees and the flue gas temps run about 400 degrees.
This would be an 80% furnace.
Gas furnace that are more efficient will take more heat out of the flue gas temps.They will add a small exhaust blower to push out the exhaust and they can even run pvc pipe for venting because the emmisions are so cool.
You'll also see heat exchangers made of stainless due to the high corrosion factor and drains taking away the liquid that the cooled flue gases caused.

Have you ever seen a wood heater with a drain hose built into the ducting?
No you have not.....
Truely you will never ever see a wood furnace or stove with the old standard of testing that is any higher than about 75%...some may be a touch higher but there is normally a high failure rate due to corrosion or burn out factor from too hot of fires.

FYI

 

[mga]

MGA I would love to see a pic and details of your unit. I have a heatilator and want to improve upon it. Sealing the doors is of interest to me. I am also interested in the grate you refer to. Any internet links?

let's see if i did this ok.....you can see the rope around the door edges. you can get that just about anywhere and it just glues on.

the grate inside is where the logs sit. in the last picture you can see where i added my little invention i'm trying. where the flex pipe ends, there used to be a blower there to blow air inside the grate and thru the pipes the logs sit on, then out thru the bottom under the glass doors.

i didn't like hearing the blower, so i removed it, ran the 4" flex thru the wall and into the basement.from there i hooked up an inducer motor and ran extra flex line to the far bedroom, where i put two wall openings with grills on them.

so....i'm drawing air from the bedroom, under the house and back into the fireplace. the negative air pressure in the bedroom draws the warm air from the room where the fireplace is. i'm just doing the same as a furnace, but in reverse.

the small yellow wire is hooked up to a digital temp sensor and i have another inside the 4" flex so i can monitor the temps in and out. not that i had to, i was curious what they were. normally, i'm pulling 65 degrees into the fire place and the air coming out varies depending on how big the fire is. i've had the air coming out over 350 at times....but the room gets too damn hot...middle of winter and i have to take my clothes off...lol so, i try to keep the fire controlled and often let it almost die out before adding new wood.

the 4" flex is my experiment and if i'm happy with how it works, i'll come up with something a bit more cosmetically pleasing. i'm also working on the blower CFM's. i'm going to try a bigger blower soon that has more CFM's and see if that does any good or not.

the switch to turn the blower on is mounted near the fireplace, so i can turn it on/off at any time. that heat stream has been in service for almost 30 years..believe it or not...has not burned thru at all and is still solid. best investment for the fireplace i ever made.

the glass door frame is also insulted and sealed around the outer edges. i put 1/2" foam insulation so that they would seal tight against the bricks, and there's fiberglass insulation inside the door frame all around.

i sealed the bottom of the door with clear high temp rtv silicone to also eliminate air leaks.

on the negative side, the glass doors will get dirty...more than usual, so, if you like your fire place looking pretty, you might think twice, but i clean mine once a month. they say not to burn a fire with the doors closed, but 99% of the time, my doors are closed and sealed tight.

 

[Scootermsp]

My Fireback:

<a href="http://s525.photobucket.com/albums/cc336/scootermsp/?action=view&current=IMG_0514.jpg" target="_blank"><img src="http://i525.photobucket.com/albums/cc336/scootermsp/IMG_0514.jpg" border="0" alt="Photobucket"></a>

 

[frogg]

Scooter <

Great idea on the cast iron plate that is what i need, where do you get it.??

Kracker

 

[turnkey4099]

These appear rather accurate. Good post. I have even seen less than that for an open hearth. The radiant heat eventually all goes up the chimney as the fire dies and drags whatever warm air that was generated right out of the house.

If the temperature outside is dropping rapidly, you could be in worse shape than you were before you lit the fire. Gasp!

Correct! I put in a 'zero clearance' heatilator that bragged about its efficiency due to built in plenum and air ducts. It disappeared shortly after there was a cold day, I kept a blazing fire going in it and was watching a thermometer in the rooom going DOWN!

An open hearth is good for only two things:

1. Very efficient way to get rid of wood.
2. Very efficient in the 'romance' department.

Harry K

 

[turnkey4099]

I read an 18th century diary kept by a Stratham, NH man named Samuel Lane who made entries almost daily for 60 years.

I've not seen his dwelling, but assume it probably had the standard chimney with 6 fireplaces - 3 downstairs and 3 up.

It was a common occurance for water on his washstand to freeze over night.

Even a Rumfordized hearth is going to pull a lot of heat up and outta the house.

Yep. and back then a winter's supply was 20-30 cord. I have heard up to 40. And that was made with just crosscut saws and ax or maul. My 'nads just shrivel up and cry uncle at the mere thought of that.

Harry K

 

[Danjensen]

thanks for the info guys.

does closing the glass front make that much of a difference?