How efficient is an open fire?

[matelot]

I think we've all read that an open fire is only 10% efficient as most of the heat goes up the chimney. Does this really matter if the heat goes up the chimney and heats the rest of the house?

 

How efficient is an open fire really? How much extra heat do you get from a log stove when it burns recirculated exhaust gasses?

 

 

[Woodworks]

Read a study some years back that in a centrally heated home it can have a negative overall effect. Literally sucks all the heat up the chimney and chucks outside. 

[spudulike]

My observation is that a log burner retains the heat and generally heats the fire breast as well as pushing much more heat in to the room. Combustion on a log burner is significantly regulated by controlling the air input with dampers (logs last longer) and it doesn't matter if the logs spit in a log burner so you can light it and go out or to bed etc with much less chance of a fire.

Log burners are much easier to light as you can control where the air is inputted.

Between the two - log burner every day of the week!

[djbobbins]

We changed from open fire to stove about 6 years ago. I can confirm it has made a big difference to the warmth of the house when the fire isn't lit - I remember sitting in the lounge one Spring and realising I could feel a draft under the door; it was the warm air getting connected up the chimney and out to the atmosphere.

We used to burn a mix of logs and housecoal, I would say that we still burn about the same amount of wood, maybe even slightly more, but no coal. The house is warmer and when the stove is not being used, we can close the vents and stop the convection of air out of the house.

I would say there are two things I miss about the open fire:

(1) the stove running on logs does not give off the same fierce heat as the open fire did, and

(2) the open fire was built of Cotswold stone and once hot would retain heat for a lot, lot longer than the chimney breast does now. Walking into the lounge on a morning and feeling the radiant heat from the chimney breast always used to put a smile on my face, but the stove doesn't heat the masonry in the same way so those days are gone :-(

[Peasgood]

51 minutes ago, matelot said:

Does this really matter if the heat goes up the chimney and heats the rest of the house?

It matters because the heat goes out of the chimney pot into the sky rather than staying (anywhere) in the house.

I have had both types of fires over the years in various houses and although I like an open fire I would never have one.

[Vespasian]

I'd say an open fire is more for ambiance than anything else.  its nice to look at the fire every now an then..  I light mine every now and then.

for heating the room its the rayburn in the kitchen..

 

 

[Haironyourchest]

I just bought an infrared remote thermometer in Lidl. Been checking my Jotul stove, the firebox is like 250 degrees and the metal stovepipe neat the ceiling is about 35. So it appears most of the heat is being trapped in the house, which is good. Thing I wonder is: is it better to pipe the air into the stove from outside ("mushroom" inside firebox) or let the fire draw air from the room and pull in new cold air through gaps or a cracked window? If the air in the room is being slowly replaced, then the temp will be lower, but the air fresher. If drawn from an isolated source via a feeder pipe, then won't the air in the room be stuffy?

[SteveA]

I've re-opened the sealed off chimney stack in our cottage and peeled off a load of woodchip wallpaper (vinyl painted) that was covering the lime plastered walls.... it's winter & we've had tons of rain yet the house has never been so dry since it was built in the early 1800's. 

So it's not just about heat.... it's also about breathability.

cheers, Steve

[onetruth]

15 minutes ago, Haironyourchest said:

I just bought an infrared remote thermometer in Lidl. Been checking my Jotul stove, the firebox is like 250 degrees and the metal stovepipe neat the ceiling is about 35. So it appears most of the heat is being trapped in the house, which is good. Thing I wonder is: is it better to pipe the air into the stove from outside ("mushroom" inside firebox) or let the fire draw air from the room and pull in new cold air through gaps or a cracked window? If the air in the room is being slowly replaced, then the temp will be lower, but the air fresher. If drawn from an isolated source via a feeder pipe, then won't the air in the room be stuffy?

I don't have much experience with stoves, but if you've got a flue with an additional internal wall (most have), the outside will be much cooler than the inside, so it's probably not as efficient as it seems.

 

As for where you draw the air from, I've never seen stoves that draw in their own air from outside.  It sounds like an expensive installation and I can't imagine it would bring much benefit (not in our climate anyway).  I'd expect a very slight efficiency boost by using room-temperature air instead of cold air, but you should get your secondary burn whichever way.  You could always open a window for a bit if it gets too stuffy!

[Haironyourchest]

1 hour ago, onetruth said:

I don't have much experience with stoves, but if you've got a flue with an additional internal wall (most have), the outside will be much cooler than the inside, so it's probably not as efficient as it seems.

 

As for where you draw the air from, I've never seen stoves that draw in their own air from outside.  It sounds like an expensive installation and I can't imagine it would bring much benefit (not in our climate anyway).  I'd expect a very slight efficiency boost by using room-temperature air instead of cold air, but you should get your secondary burn whichever way.  You could always open a window for a bit if it gets too stuffy!

My stove is single wall until about 6 inches from the ceiling. Measurement taken from the single wall pipe. You can track the Lazer down the pipe and see the temp going up and up the closer you get to the stove. The outside Aire system was common in open fires, usually with a manual "blower" somewhere near the fire that you'd crank a handle. I think it was a rich man's gadget, don't know if they really work that well, but in a closed stovebox I imagine it woukd...