Minimum temp for chimney outlet?

[larboc]

Yea, it was cold here too-below average. Lake superior had ice till june, water lines 9 feet deep were frozen till june 12th at one guys place. Not sure what zone 4 means, we are similar to thunder bay. Get a lot of their radio stations/air tv stations.

 

[rideau]

I'm sure you are colder than we are. But we are cold. And I do hope you get by with a lot less than ten cords. Will be very interested to here how the wood usage is going in a month or two. Good luck with it.

 

[Highbeam]

I have logged wood usage in my mild climate. In my non-cats I burned as much as 7 cords and now the BK burns at least 4 cords. Average was 5. I live in smallish house, a relatively moderate climate, but a long burn season. While ten is high, I think 3 is silly low.

 

[larboc]

UPDATE:

Just under 10 cords of indoor heated stored, well seasoned and checked hard maple, red oak, and ironwood this winter. Coldest february on record this year, mean temp of right about zero where I'm at. I had the lowest temp at -30.6F. Another 1.5+ months of shoulder heating season ahead so I'm guessing I'll be right at 10

To summarize the majority of the winter usage: I think my calculations were fairly close, the lopi wastes heat when run hard as a result of poor heat extraction. With a few back to back week long comparisons of the 80's Humble wood furnace in the basement compared to the insert I can say with confidence the Lopi used half again more wood than the furnace when heating demand was very high. In order to keep the house warm, I was firing the lopi at about half throttle most of the time and the stack out temps were in the 400F-700F degree range, sometimes over 800F at WOT. Shoulder season like now the lopi does fine because I can throttle it back to almost idle and keep the house warm and the stack temps are around 250-300. This time of year I think the humble would clog up the stack running such low heat output so the lopi works great for that. I had to clean the chimney for the Humble a few times in the fall before I had the insert when heating demand was low.

The "smoke dragon" in the basement has cooler outlet temps at the roof as a result of the heat recovered into the house through the clay lined centrally located masonry flue.

Both chimneys are clean, never had to clean them this winter. The lopi's liner has brown dust in it, the humble has a normal thin layer of creosote

In hindsight, I wish I had gone with a non-insulated liner for my insert so that the heat could have been recovered into the chimney and then the house, the lopi burns hot and clean but like all inserts doesn't have a means to extract as much heat as it could. I would assume this is done for the typical installation with an un-insulated liner needing more gas temp to keep creosote formation down. I may cut some of insulation off that I can get to.

To summarize, the insert is great for lower heating demands and probably does have it's peak efficiency right where the EPA sticker says at 30,000 btu's or so. It will pump out 100,000 but but will send a lot of the heat up the stack. Perfect for shoulder seasons, radiant heat to stand next to, help when it's super cold and you need to clean ashes out of the big furnace, and anytime you want some cheer! I would not go with an insulated liner again.

I still think the Lopi Freedom is probably the best large insert, at least for my application. I don't see any inserts that have any better heat exchanger on them. Next year I think I might try setting some large aluminum heat sinks on the cooktop to help draw heat out, and remove some liner insulation.

YMMV!

 

[begreen]

The Grandview insert has a finned heat exchanger IIRC. Some cat stoves claim higher efficiencies and run with cooler stacks.

 

[Isaiah53]

A key point you are not considering in your temperatures is that the key parameter that affects creosote condensation is the temperature of the inner wall of your liner, not the bulk flue gas temperature that you are measuring. The inner wall will always be colder than the bulk flue gas and consequently creosote forms on the walls of the chimney. Keeping the wall temperature hot is the key to minimizing creosote condensation. That is why liners and especially double wall or insulated chimneys are so effective in preventing it and recommended. It creates an insulation barrier that keeps the inner surface that is exposed to the flue hot enough to prevent condensation. That is also the reason the exit or cap is so vulnerable to condensation - because it is exposed the outside air and will be much colder. If you are running your bulk flue gas at 212 or even 250 F, the wall temperature is likely to be one-third to one half of that at least near the cold exit and creosote is going to form.

 

[DanCorcoran]

Running full tilt, the factory circulation blower can't really do much to the flue exit temperature.

I don't know about flue "exit" temperature, but I turn on my factory blower whenever my Condar flue probe (18" above the stove) starts going into the red. That temperature begins to stabilize and then starts dropping quite quickly. I assume the flue exit temperatures reflect this change as well.

 

[ddahlgren]

800 is silly hot. I can say burning 2 1/2 to 3 cords of seasoned wood and some that could have been a bit better that 500 12 inches from the stove with a probe type thermometer I had zero creosote and that is with 7 feet of single wall pipe inside and 5 feet of duravent plus going through roof and the rest out doors. I would think anything in the 300 to 350 range would be just fine if you place the upper thermocouple 1/2 inch from the surface of the pipe at the top. I think the first thing I would do is by a Dwyer MK II manometer and get a handle on what your draft is compared to what the stove needs. Excessive draft is generally the largest heat loss no matter what the fuel is. It might be something as simple as a manual pipe damper will slow it down to reasonable and give you more control over burn rate at the same time. I hate having to use a lot of electricity to get more heat as around here after taxes etc. it is 26 cents per kwh and adds up quick. Trading 200 worth of wood for 600 worth of electric makes no sense. I would suspect getting control of the draft would also extend burn time especially during the high part of the cycle and stretch that part out. Total cost for the MK II and damper well under 50 bucks and an hour of of your time.

 

[blades]

There were some very interesting stove designs prior to stateside Epa screwing up the industry( or how ever you care to look at it or describe it) One in particular came out of upper Minn. Non cat -heat exchanger system in top 1/3 of stove but was not in the exhaust stream and therefore did not present the problems associated with the Magic burn your house down device ( indirect heat transfer design vs direct of magic unit). Due to the expense of the testing to be compliant with EPA an awful lot of these forward thinking designs went south. This particular one did not use electronics ( which the addition of defeats the purpose of a wood stove to a lot of us - ie no power no heat and of course that high heat and electronics do not mix unless the controller system is remote) Another side of the coin is profits to be made by the company - and therefore risk of an off the wall design ( lets face facts wood burners( humanoids that is ) are not the most pliable when it comes to change) does not represent the best policy vs profits. The arduous process of becoming epa compliant coupled with start up costs has put an extreme damper on innovation( outside the box type) within the wood burning industry. Not very many have the pocket depth to achieve the goal line. Not to mention that the possible return in investment is quite low for a considerable time period - doesn't make a good business plan for investors at all. just my observations yours maybe quite different - But I am older quite set in my ways and quite a grouch when it comes to whipper snappers behind a desk telling me what I can and can't do with no real world experience besides pencil pushing.

 

[ddahlgren]

When I got divorced from my first wife I got custody of both kids at 3 and 5 more or less. hey would send a social worker by from time to time to see how I was doing, house clean food ok clean clothes all that stuff. The social work fresh out I would guess junior college but who knows. She had all these suggestions and some things I needed to do in order to keep custody of the kids. She seemed to have a problem with me making them eat their dinner if they did not like the name of the food but never had it. They had told her if they did not eat dinner it was breakfast the next morning and nothing between dinner and breakfast unless they wanted to finish their dinner cold. I asked her how many kids she had for practical experience and of course none. Told her outright time for her to leave and send over someone that has kids for 5 years or more as she is working with theory only so nothing about real world. No one ever bothered to stop by LOL.

Same with a lot of stove regs we are not running them in a lab with perfect fuel and really need heat so don't want the cleanest burning incinerator possible. To me half of the new wood stoves are basically wood incinerators. 800 degrees is an incinerator temp and no need for it in my mind. I would think the simplest way to recover more heat is more heat exchanger surface area and a longer path from fire to chimney to give the heat up by convection with no extra devices needed. 6 1/2 feet of single wall pipe will double the surface area of the average stove and have no idea of why people use insulated pipe indoors. Changing to single wall would add 6 to 8k btu/hr.at 300 to 400F. I equally never saw the usefulness of a fireplace insert. Granted better than a fireplace but with no exposed stack pipe and 80% of heat exchanger inside fireplace all you have left is the door and whatever the fan can do.

 

[Oldman47]

ddahlgren, I have double wall for a reason. If I ran single wall as you suggest I could extract a bit more heat from my combustion but at what cost? Every BTU that I get doing that costs me in terminal temperatures in the chimney. If I am very efficient and extract lots of BTUs from using single wall where is my flue exit temperature? Maybe I can hold the chimney exit at 200ºF but that would mean terrible creosote build ups. If I am already holding my chimney exit temperature at 250ºF, I have removed every BTU that I should from my flue gas. Any more is not a positive effect, it is trading BTUs for creosote, which is a losing proposition in my opinion.

 

[ddahlgren]

ddahlgren, I have double wall for a reason. If I ran single wall as you suggest I could extract a bit more heat from my combustion but at what cost? Every BTU that I get doing that costs me in terminal temperatures in the chimney. If I am very efficient and extract lots of BTUs from using single wall where is my flue exit temperature? Maybe I can hold the chimney exit at 200ºF but that would mean terrible creosote build ups. If I am already holding my chimney exit temperature at 250ºF, I have removed every BTU that I should from my flue gas. Any more is not a positive effect, it is trading BTUs for creosote, which is a losing proposition in my opinion.

You have a very rare stove that can run with that low a flue temp. Are you burning seasoned wood? Wood with too high a moisture content does burn very cold like you describe. The original poster had an exit temp up to 500 at chimney top and way too high in my mind. Most others with seasoned wood run just like his as well.

 

[Oldman47]

At the stack outlet 250ºF should be easy as can be. Reduce your firing rate and the flue gas will cool enough within the stack itself to get there. I think Isaiah said it best.

"That is also the reason the exit or cap is so vulnerable to condensation - because it is exposed the outside air and will be much colder. If you are running your bulk flue gas at 212 or even 250 F, the wall temperature is likely to be one-third to one half of that at least near the cold exit and creosote is going to form."

 

[larboc]

800 is silly hot. I can say burning 2 1/2 to 3 cords of seasoned wood and some that could have been a bit better that 500 12 inches from the stove with a probe type thermometer I had zero creosote and that is with 7 feet of single wall pipe inside and 5 feet of duravent plus going through roof and the rest out doors. I would think anything in the 300 to 350 range would be just fine if you place the upper thermocouple 1/2 inch from the surface of the pipe at the top. I think the first thing I would do is by a Dwyer MK II manometer and get a handle on what your draft is compared to what the stove needs. Excessive draft is generally the largest heat loss no matter what the fuel is. It might be something as simple as a manual pipe damper will slow it down to reasonable and give you more control over burn rate at the same time. I hate having to use a lot of electricity to get more heat as around here after taxes etc. it is 26 cents per kwh and adds up quick. Trading 200 worth of wood for 600 worth of electric makes no sense. I would suspect getting control of the draft would also extend burn time especially during the high part of the cycle and stretch that part out. Total cost for the MK II and damper well under 50 bucks and an hour of of your time.

Re-read what I wrote. Of course I can control the draft, but that reduces the airflow through the stove which reduces the heat output. In order to make enough heat to heat the whole house in the coldest parts of the season it required wide open damper settings. My point was that the stove shouldn't be operated at full tilt, it should be run closer to the EPA rated btu output which I think is around 30,000 btu unless heat is recovered in a secondary heat exchanger, otherwise you're losing a lot of heat out the chimney compared to a traditional wood furnace with a long, un-insulated interior chimney.

Bottom line is insulated liners are a bad idea if your chimney is interior to the house and you have significantly high heat output expectations of an EPA insert and you don't have room for a reclaimer in the stack.

 

[Grisu]

Re-read what I wrote. Of course I can control the draft, but that reduces the airflow through the stove which reduces the heat output. In order to make enough heat to heat the whole house in the coldest parts of the season it required wide open damper settings.

Not at all. I can reduce the air to its lowest setting and still get the stovetop to 700 F, sometimes even 750 F. Leaving the air open more will only lead to either sending more heat up the flue or increasing the stovetop temp to potential overfire conditions. If you need to run the stove as you describe than you likely have a draft and/or fuel problem.

Bottom line is insulated liners are a bad idea if your chimney is interior to the house and you have significantly high heat output expectations of an EPA insert and you don't have room for a reclaimer in the stack.

You heat with the stove, not the chimney. Insulating the liner is almost always better. And as bholler likes to point out: Most masonry chimneys are not built with the required clearances. Thus, insulating the liner is required for safety reasons.

 

[DanCorcoran]

Not at all. I can reduce the air to its lowest setting and still get the stovetop to 700 F, sometimes even 750 F. Leaving the air open more will only lead to either sending more heat up the flue or increasing the stovetop temp to potential overfire conditions. If you need to run the stove as you describe than you likely have a draft and/or fuel problem.


You heat with the stove, not the chimney. Insulating the liner is almost always better. And as bholler likes to point out: Most masonry chimneys are not built with the required clearances. Thus, insulating the liner is required for safety reasons.

Whether it's called a flue or a chimney, mine is single-wall and I heat with it as well as with the stove, per attached photo:

 

[bholler]

You have a very rare stove that can run with that low a flue temp. Are you burning seasoned wood? Wood with too high a moisture content does burn very cold like you describe. The original poster had an exit temp up to 500 at chimney top and way too high in my mind. Most others with seasoned wood run just like his as well.

No most people with seasoned wood don't run anywhere near 500 at the top of the stack. And the op said it was 500 wide open you should never be running your stove that way for extended periods of time.

 

[kennyp2339]

In my own opinion, what it comes down to is safety, There will always be the argument of insulated vs non insulated. While I prefer insulated in my situation, I have ran a single wall pipe to. I think it for amount of heat coming off the single wall its not worth while in the big picture. I think we just convince ourselves that the heat in the chimney could be extracted rather than wasted. If you have a good draft and want to run single wall go for it, just inspected your chimney once a month to make sure your not clogging up.
I rather run double wall because I know I can achieve higher flue gas temps which reduces my chances for creosote build up, I really don't have the drive anymore to balance on my icy snow covered roof and check / sweep the chimney every month, not that it needed it, but it makes me sleep easier at night knowing my flue is clean.

 

[kennyp2339]

Whether it's called a flue or a chimney, mine is single-wall and I heat with it as well as with the stove, per attached photo:

View attachment 159992

Nice setup -

 

[ddahlgren]

Why isn't the heat in a single wall stack fair game to reclaim? I use a probe to measure gas temp the magnetic ones while cheap are a joke. I keep the probe on wood above 300 and the magnetic one says I am way too cold yet chimney sweep never found any creosote. By the same token gone to the dark side and burn coal now and can get the probe down to 120 with stove top 250 or crank the stove top to 750 if -20 and winy outside. a whole different world but still burn wood in spring and fall to take the chill off before serious heat is needed.

 

[blades]

Couple of interesting designs being bandied about for flue sections stove to ceiling involving a cat external to stove and heat exchanger system. Trick here is a cat system that operates at the lower temps range than that typically associated with them. Auto draft control on exhaust is another area being explored, this is typicaly the fall down area of EPA certified stoves( not a barometric unit like we see currently as these cause more problems than help by introducing unheated air in the exhaust stream in an effort to reduced the draft rate)
Currently due to EPA a lot of research has been directed at particulate emissions - combined with the aesthetics of keeping glass clean, yada yada, which imop has cost efficiency in btus actually used for heating purposes. In this respect some of the newer European designs are ahead of the curve - but are typicaly smaller units than what is more commonly used stateside - just because European homes on average are a much smaller foot print. I would hazard a guess that smaller stoves are also simpler to achieve particulate emission rates as well.

 

[Squirrel]

I have a small efficient European stove. I also have an efficient straight shot chimney with excellent draft. The outlet on the stove collar is 5" and in Europe it would have a 5" flue. Although the dealer and installer agreed that a 5" flue would probably work well the "Rules" say it has to have a 6" flue. The result is that when it's -40* outside icicles form around the outside edge of the rain cap, even with the stove wide open. There's just not enough wasted heat to keep a large stainless plate warm.
Sometimes rules are just not good things compared to thought, knowledge and experience.

 

[blades]

I have a small efficient European stove. I also have an efficient straight shot chimney with excellent draft. The outlet on the stove collar is 5" and in Europe it would have a 5" flue. Although the dealer and installer agreed that a 5" flue would probably work well the "Rules" say it has to have a 6" flue. The result is that when it's -40* outside icicles form around the outside edge of the rain cap, even with the stove wide open. There's just not enough wasted heat to keep a large stainless plate warm.
Sometimes rules are just not good things compared to thought, knowledge and experience.

Whose rule says it has to be 6"?

 

[Grisu]

Maybe Canada is different but usually the flue size should match the outlet of the stove. Did you contact the manufacturer with which pipe the stove had been tested for the Canadian market?

 

[begreen]

Whether it's called a flue or a chimney, mine is single-wall and I heat with it as well as with the stove, per attached photo:

View attachment 159992

This is not a recommended practice by the stove or pipe mfg.. From the Shelburne manual:
Long runs of stovepipe to increase heat dispersal are not recommended.