Confusion around stove temp and and blower control.

[bholler]

Thanks for your comments.

Recommending that the firebox be loaded to a limited level is the only objective guidance on how big a fire to build. We agree that there is no specific objective guidance as to what an overfired condition is. So I continue to suggest that the recommended amount of fuel is the best guide available.

You are happy firing your stove to a temperature of 600-700 degrees by measuring the surface temperature of the stove. My stove manufacturer provided me with no such guidance, so I decided for myself what was reasonable. A stack temperature of 600 degrees is a good maximum that I aim for. If a fire boosts the stack temperature to 700 degrees I'm looking to cut that down.

You seem to have great confidence in your recommendations, having never seen either stove. I suggest that may be misplaced in both cases.

I used to analyze the combustion of gas furnaces and boilers after conversion burners were installed. A conversion burner allows a very wide range of fuel and combustion air to be directed into the equipment, making it necessary to use instruments to test the combustion for satisfactory levels of CO2, oxygen, stack temperature and carbon monoxide. All of these characteristics can vary widely, and usually the combustion air and gas input can be adjusted to bring about a safe and efficient operating condition. So for me, using a stack temperature as a guide to operation is natural, and I happen to have a good thermometer to use for that purpose.

Perhaps I'll buy a thermometer for measuring the stove surface temperature and compare that with the stack temperature. It sounds like your time spent using a wood stove has been spent knowing the stove surface temperature but not the stack temperature of the actual combustion products.


<<The manual is a reference, and not a wood burning bible. They keep it vague because every application & system is different. Yes there is some common ground between all stoves, but the manual is kept limited in info for a reason.

I usually hear comments like that from people who are substituting their own judgement for that of the people who designed their equipment.

<<As has been said many times, just because a person claims to have burning for 20,30,40,50 years, does not necessarily mean they have been using the best burning practices. At 600 degree stack temp, you have a bunch of heat going up and out, that is fact.


Well, I'l agree that that is an OPINION. A fact would be to do a combustion analysis of the flue gasses and stack temperature, which you have never done and which I haven't done with my stove. Actually, running 600 degrees is hotter than I prefer to do. It's really the maximum I'd see before taking active measures to reduce the stack temperature. My main concern is overfiring the stove. At 700 degrees I'd take positive action to cut down the temperature, at 600 degrees I'd typically let it burn down further on its own.

I don't suppose you have a reference to someone who has done that kind of combustion analysis on different stoves, allowing the actual efficiency to be determined? That's the practical real way to test and determine efficiency that I know about. My opinion and experience is my opinion and experience, and the same for you, my friend.

Do you have any references to recommended stack or stove surface temperatures? I've never seen any guidance on that, but perhaps it's out there somewhere. Comparisons between stove surface temperature and stack temperatures and recommendations on either or both of those I'd be glad to see as well, if you can refer me to that kind of information.

I'll look around and see if I can find information on recommended stack temperatures for gas, oil, coal and wood fired equipment. Perhaps there's some useful guidance out there somewhere.

I suggest that with most fuel burning equipment, measuring surface temperature isn't of much use, since appliance surface temperatures usually aren't exposed to the fire. Stack temperature is, I suggest, a far more widely used way to understand the heat being produced by the appliance.

But surface temperature on a typical wood stove may indeed be useful, since if you choose a suitable place to measure the temperature it ought to reflect .the combustion that is taking place. Even so, measuring the surface stack temperature would seem to me to be a more sensitive guide to what is happening.

Thanks again for your interesting and useful comments, bringing up ideas I hadn't considered in detail before.

You do realize that your expertise in servicing gas or oil fires appliances does not translate into wood burners right?

What stove do you burn? How and where are you measuring that 600 degrees stack temp? If it is internal temp it is a bit high but not bad. If that is measured on the surface of the pipe it it is way to high. Any of the many stoves i have run would be overfireing at that temp. And you are wasting massive ammounts of heat up the stack. And exceeding the normal operating temp of your chimney.

 

[wooduser]

You do realize that your expertise in servicing gas or oil fires appliances does not translate into wood burners right?

What stove do you burn? How and where are you measuring that 600 degrees stack temp? If it is internal temp it is a bit high but not bad. If that is measured on the surface of the pipe it it is way to high. Any of the many stoves i have run would be overfireing at that temp. And you are wasting massive ammounts of heat up the stack. And exceeding the normal operating temp of your chimney.

Hello bholler,


Thanks for you reply.

I have an uncertified steel stove from circa 1987. I have a hole in the flue pipe about two feet above the stove and measure the temperature with a good quality Bacharach "tempoint" flue gas thermometer.

The stack temperature I use is largely determined by the heat loss of my house, and thus the amount of heat I need to maintain an acceptable room temperature. I generally like to maintain a temperature somewhere between 300-600 degrees, depending on how much heat I need to maintain room temperature.

So on a really cold night, I might stoke up the stove to a 600 degree level, and accept a lower efficiency in the interest of keeping the temperature up. Other times I might build a small hot fire to heat up the room, and let it go out and the room to cool down over a period of an hour or more.

Efficiency, after all, is not the end all and be all of operating a stove. Producing an acceptable level of heating for your speace is generally my priority.

My main experience was as a gas appliance repairman for a natural gas utility. I see lots of commonality between all kinds of fuel burning appliances, and lots of differences as well. Just depends upon what you are talking about. Measuring the surface temperature of a wood stove might produce useful information, while measuring the surface temperature of a gas forced air furnace would be meaningless of course. Measuring the stack temperature of both would provide useful information about the combustion of both, along with useful information about coal and oil stoves or furnaces.

But I've never had technical training on the operation of wood stoves or wood fired equipment. (I do my own chimney sweeping in my all fuel chimney). I will be glad to some technical information on how to determine safe rates of combustion, measuring efficiency and such as people choose to discuss such issues.

I suspect that measuring efficiency involves analyzing the temperature and chemical composition of flue gasses for wood, gas, oil or coal, although each fuel would have it's own preferred ranges of course.

But again, efficiency isn't necessarily the most important issue for wood stoves in homes, I suggest. Safety and comfort ranks higher than efficiency, it seems to me.

And how to measure an overfired condition in the absence of a manufacturer's recommendation? I don't have any clear idea of that, just my seat of the pants experience.

 

[bholler]

Hello bholler,


Thanks for you reply.

I have an uncertified steel stove from circa 1987. I have a hole in the flue pipe about two feet above the stove and measure the temperature with a good quality Bacharach "tempoint" flue gas thermometer.

The stack temperature I use is largely determined by the heat loss of my house, and thus the amount of heat I need to maintain an acceptable room temperature. I generally like to maintain a temperature somewhere between 300-600 degrees, depending on how much heat I need to maintain room temperature.

So on a really cold night, I might stoke up the stove to a 600 degree level, and accept a lower efficiency in the interest of keeping the temperature up. Other times I might build a small hot fire to heat up the room, and let it go out and the room to cool down over a period of an hour or more.

Efficiency, after all, is not the end all and be all of operating a stove. Producing an acceptable level of heating for your speace is generally my priority.

My main experience was as a gas appliance repairman for a natural gas utility. I see lots of commonality between all kinds of fuel burning appliances, and lots of differences as well. Just depends upon what you are talking about. Measuring the surface temperature of a wood stove might produce useful information, while measuring the surface temperature of a gas forced air furnace would be meaningless of course. Measuring the stack temperature of both would provide useful information about the combustion of both, along with useful information about coal and oil stoves or furnaces.

But I've never had technical training on the operation of wood stoves or wood fired equipment. (I do my own chimney sweeping in my all fuel chimney). I will be glad to some technical information on how to determine safe rates of combustion, measuring efficiency and such as people choose to discuss such issues.

I suspect that measuring efficiency involves analyzing the temperature and chemical composition of flue gasses for wood, gas, oil or coal, although each fuel would have it's own preferred ranges of course.

But again, efficiency isn't necessarily the most important issue for wood stoves in homes, I suggest. Safety and comfort ranks higher than efficiency, it seems to me.

And how to measure an overfired condition in the absence of a manufacturer's recommendation? I don't have any clear idea of that, just my seat of the pants experience.

Ok because you are measuring internal pipe temp the temperature range you are using is pretty reasonable although at 300 you are getting pretty low and depending on your chimney setup may be dropping below the condensation temp before the exhaust exits the chimney. But if you have an insulated flue that is not to tall it is probably fine.

As far as pipe versus top temp either works. Many of us prefer to measure both. And others with cat stoves dont use either just cat temps.

As far as safe temps generally steel or cast stoves with out a convective top should be kept under 800. A little above that is no big deal but you shouldnt make a habit of it.

As far as flue temps it should stay below 1000 internal or 500 surface. And for most chimneys 450 or so internal or 225 surface is a good low range but those are approximate. And of course once it is down to coals you can safely drop. And if you have a good chimney setup you can also run a little cooler.

Be aware that most of the stove we are talking about in this board are run very differently than yours. Modern clean burn stoves use several different combustion techniques to burn cleanly and efficiently. And each one needs to be run differently.

 

[wooduser]

Hello bholler,

Thanks for your evaluation. I use 6" single wall pipe from the top of the stove to the eight foot ceiling, then all fuel chimney through the ceiling and roof to the top of the chimney with a chimney cap on it.

Just off hand, that's about five feet of single wall pipe then about 5-6 feet of all fuel chimney.

My Bacharach Tempoint Thermometer is a probe style thermometer of good quality left over from my days as a furnace repairman:
(broken link removed to https://www.ebay.com/itm/BACHARACH-Dec-14-Dec-14-TEMPOINT-STACK-THERMOMETER-1000F-6/202118974350?epid=1459218008&hash=item2f0f3acb8e:g:tjYAAOSwLg5bV1mP)

<<As far as pipe versus top temp either works. Many of us prefer to measure both.


I think I'll get a surface mount thermometer, mainly to compare the temperatures, and to be able to offer information more people on this board use, apparently. And now I'm curious!

<<As far as flue temps it should stay below 1000 internal or 500 surface.

I doubt that I've every come anywhere near 1,000! When I get to 700 internal stack temperature with my probe thermometer, I'm looking to reduce the temperature. I don't have any authoritative reference for doing that, just that I want to avoid overheating the stove and chimney and that seems reasonable.

I appreciate your numbers, but where do they come from? That's what I'm looking for now.

The manufacturer of my old "Fuego" steel stove never specified what an overfiring condition was. So what do those designing wood stoves recommend ?

In particular, I'm supposing that the manufacturers of all fuel chimney ought to specify maximum operating stack temperatures for their products----perhaps I'll look for information among those products.


Thanks again for your comments and advice, which is giving me ideas I can pursue.

 

[bholler]

Hello bholler,

Thanks for your evaluation. I use 6" single wall pipe from the top of the stove to the eight foot ceiling, then all fuel chimney through the ceiling and roof to the top of the chimney with a chimney cap on it.

Just off hand, that's about five feet of single wall pipe then about 5-6 feet of all fuel chimney.

My Bacharach Tempoint Thermometer is a probe style thermometer of good quality left over from my days as a furnace repairman:
(broken link removed to https://www.ebay.com/itm/BACHARACH-Dec-14-Dec-14-TEMPOINT-STACK-THERMOMETER-1000F-6/202118974350?epid=1459218008&hash=item2f0f3acb8e:g:tjYAAOSwLg5bV1mP)

<<As far as pipe versus top temp either works. Many of us prefer to measure both.


I think I'll get a surface mount thermometer, mainly to compare the temperatures, and to be able to offer information more people on this board use, apparently. And now I'm curious!

<<As far as flue temps it should stay below 1000 internal or 500 surface.

I doubt that I've every come anywhere near 1,000! When I get to 700 internal stack temperature with my probe thermometer, I'm looking to reduce the temperature. I don't have any authoritative reference for doing that, just that I want to avoid overheating the stove and chimney and that seems reasonable.

I appreciate your numbers, but where do they come from? That's what I'm looking for now.

The manufacturer of my old "Fuego" steel stove never specified what an overfiring condition was. So what do those designing wood stoves recommend ?

In particular, I'm supposing that the manufacturers of all fuel chimney ought to specify maximum operating stack temperatures for their products----perhaps I'll look for information among those products.


Thanks again for your comments and advice, which is giving me ideas I can pursue.

Those temps come from years of experience and training in this feild. On your stove there wont be allot of difference between the stovetop and the pipe on modern stoves it is pretty common to see the stove top double the surface temp of single wall pipe.

And class a prefab chimneys do clearly state their operating ranges. Maximum continuous flue temp is 1000 total max is 2100.

 

[Hogwildz]

You cannot compare gas & oil fired burners to a wood burner. Well you can, but they are completely different beasts.
You want info on stack temps, do a search of this forum. There are many posts to read by real usage members that have provided plenty of useful info on stack temps & stove top temps. And it is widely common knowledge that stack temps should be lower than stove top temps. Stove top on most stoves is the hottest part of the firebox to take a temp reading. Nothing wrong with stack temps at all, but they should be two different temps, with the flu temp being lower. As has been reported by many members here using both stove top & flue thermometers. I don't have the luxury of a flue thermo as I have an insert. If your stack temp is even 600, that is a bit high. Don't take my word for it, search the posts here, and you'll get a good idea from other members posts. You did say you're burning a 30yr old stove, so I would expect the flue to be hot as you have no secondary burn system or cat to slow the flow. Again sending hotter gas up the stack, which is a waste. I bet that puppy eats a ton of wood also. How often do you get to burn that ol pup in the Seattle area?

Not sure how you are getting away with burning a 30yr old wood stove in Seattle, but no matter to me.
The other thing that you may want to consider is newer stoves burn completely different than what you are burning in.

 

[ColdNorCal]

Hello, and thanks for reading and your time to respond if you choose to.

I have an Englands Wood Stove (Model 13-NC) with a glass front. I am concerned because often after putting a large log in the stove, my thermostat often shoots up into the > 600-degree range, which I have been advised is an 'overburn' area and can cause a chimney fire. I have the chimney cleaned regularly, but still, it makes me nervous to put a log in and leave the house, or overnight.

The stove _does_ have a blower on it, that if I turn on, will cool the stove down to a better temperature range of, but it is a manual blower, meaning I would have to either always have the blower on while I am gone or all night long which isn't ideal.

So, I looked into installing a thermostat magnet switch for the blower that would turn the blower on when the stove got up to 55o degrees, lets say, but all the thermostat switches I can find will turn on at 110 degrees, and off at 90 degrees, which is so much lower than the temps I am dealing with, I am confused what I am missing.

Can anyone advise to me how to correctly rig up a temp sensor switch to my blower to have it come on at higher temperatures, or advise about some other solution that I have not considered?

Thanks again
J

I installed a 120/90 temp switch from Amazon. I read your post a few days ago and wondered when the 120/90 temp switch kicked on. I knew it was not when the stove top was 125, it was much later at a higher temp. The past two days after cold start, I left the fan on and waited for the temp switch to turn on. Both times the temp switch turned the blower on at 450~475 degrees stove top temp.

The temp switch sensor is mounted on the rear heat shield over an existing hole that is there for a factory temp switch. In other words, the actual temp switch sensor is not touching any metal portion of stove. It is being triggered by the air temp between rear of stove and rear heat shield.

I dont know at what temp the switch will turn off the blower as I turn if off manually.