Tired of 300F going up the chimney

[skibumm100]

Nope. It's done with a contact K thermocouple right on the exhaust exit housing from the blower. This is AFTER I made the mods to my stove. If you're measuring 380 degrees, I would guess your heat exchanger isn't 'exchanging' due to build up of ash or your exhaust blower is running too high and not giving your exhaust enough time to exchange heat.

Realize that the temps I took were to measure relative exhaust temps before and after my mods to prove that I was extracting more heat with the mods. We aren't measuring the exact same thing BUT I seriously doubt that there would be a 200 degree delta T between the gases and the steel.

Now you've got me hooked. Sorry...a little OT. Do you have a description of your mods? My OAK temp is 110-125 deg F so it' unlikely I will see exhaust temps around 160 deg F. What were you exhaust temps pre-mod vs. post-mod? My insert room outlet temps are high 200's so I think I'm doing OK with HX.

 

[Mr. Spock]

The article was clearly written to address wood stoves but this little paragraph says it all >
" You can either keep the chimney above 250 degree F all the way out the top or, you can burn up the gases that form the creosote in the stove before they reach the chimney. Modern stoves do the latter and capture the heat produced by essentially burning the smoke.. This is true of stoves with catalytic converters and non-cat stoves that burn gases by recirculating them. Either way, less smoke means less creosote. Burn the smoke and you burn the gases. No gases, no creosote. As simple as that."
So for a 'modern' pellet stove, I would assume we are doing the latter if we are competent enough to maintain the stove so that it gets the proper fuel/air ratio to burn those gases. There's no way that you are going to keep the flue above 250 all the way up a chimney. I've never seen smoke out the top of my chimney except for the initial light off either.
We have to be careful just spitting out blank statements which newcomers will take as the absolute truth.

No debating the facts you have carefully pointed out. I was rushed in getting my comment out and I see my original statement didn't come across quite right. I was just trying to state two facts to think about. The gases from wood burning do form creosote below 250. And it is playing with fire. I mean literally. Aren't we all? It was just a play on words that apparently did not come out right.

Now true our pellets stove do a great job burning wood product cleanly. That does not mean circumstances will not change that. So when we start to modify our setups outside recommended installation practices lets keep safety in mind.

Sorry to interrupt, please continue with the regularly scheduled programming.

 

[SwineFlue]

Now you've got me hooked. Sorry...a little OT. Do you have a description of your mods? My OAK temp is 110-125 deg F so it' unlikely I will see exhaust temps around 160 deg F. What were you exhaust temps pre-mod vs. post-mod? My insert room outlet temps are high 200's so I think I'm doing OK with HX.

https://www.hearth.com/talk/threads/quadrafire-castile-experiment.58216/

Enjoy!

Edit: and here's another mod thread: https://www.hearth.com/talk/threads/my-quadrafire-1200-re-anaysis.75329/

 

[greythorn3]

you could put a trap in it and collect the condensation to use for making hot chocolate to drink. might get a extra thrill outa some carcinogens in the condensation/coco too.

 

[tjnamtiw]

No debating the facts you have carefully pointed out. I was rushed in getting my comment out and I see my original statement didn't come across quite right. I was just trying to state two facts to think about. The gases from wood burning do form creosote below 250. And it is playing with fire. I mean literally. Aren't we all? It was just a play on words that apparently did not come out right.

Now true our pellets stove do a great job burning wood product cleanly. That does not mean circumstances will not change that. So when we start to modify our setups outside recommended installation practices lets keep safety in mind.

Sorry to interrupt, please continue with the regularly scheduled programming.

You're right. The only place I've found creosote after 3 full years of burning is on the right hand set of heat exchanger tubes if I run it on low too long. That tells me that I may not have enough combustion air on low, which is something I haven't played with.....yet. If I could, I'd program in a higher setting on the blower or a lower time on the auger cycle. A one hour burn on high clears things up.

 

[Mr. Spock]

You're right. The only place I've found creosote after 3 full years of burning is on the right hand set of heat exchanger tubes if I run it on low too long. That tells me that I may not have enough combustion air on low, which is something I haven't played with.....yet. If I could, I'd program in a higher setting on the blower or a lower time on the auger cycle. A one hour burn on high clears things up.

Same thing here but I get it on the sides of the burn box if the XXV has prolonged low burns. My fix is the same - let her rip and run hot for a while. Opening windows follows but it cleans her right up.

 

[hossthehermit]

After seeing what a magic heat did on pellet venting. You'll need to keep an eye on it and if burned at low temps with condensation you might see creosoot build up..

Where's Pook when ya need him ??????????????????

 

[sportbikerider78]

Yes, that's a good idea too. Its single wall thick pipe and installing some kind of finned aluminum sleeve around it would still be better than nothing. I've seen something like that for oil filters. If this flops I'll see what can be done with that mod.

That is ridiculous setup on that oil filter. Relying on conduction heat when only about 10% of your surface area of the ID of that heatsink is touching, is just plain silly. That is a gimmick. You'd be better off scrapping the paint off that oil filter to give better convection heat. Paint insulates.
(I'm ignoring the fact that oil filters are paper thin metal and they have a thumbscrew to hold that contraption on.)

To the OP. You are re engineering the wheel. You are finding a way to remove more heat from the exhaust gasses. Why not simply improve the air flow through the stove by upgrading the existing fans? This is exactly the same as what you are currently doing, but with less effort. Just a thought. Cool project though!

 

[jtakeman]

Why not simply improve the air flow through the stove by upgrading the existing fans? This is exactly the same as what you are currently doing, but with less effort.

Or improving the stoves heat exchanger to increase heat transfer to the convection path. The more heat you extract, The less goes out the venting.

 

[tjnamtiw]

That is ridiculous setup on that oil filter. Relying on conduction heat when only about 10% of your surface area of the ID of that heatsink is touching, is just plain silly. That is a gimmick. You'd be better off scrapping the paint off that oil filter to give better convection heat. Paint insulates.
(I'm ignoring the fact that oil filters are paper thin metal and they have a thumbscrew to hold that contraption on.)

To the OP. You are re engineering the wheel. You are finding a way to remove more heat from the exhaust gasses. Why not simply improve the air flow through the stove by upgrading the existing fans? This is exactly the same as what you are currently doing, but with less effort. Just a thought. Cool project though!

You must not be familiar with an oil filter because only the very end of the filter has the 'scallops' to engage the filter removal tool, hence the '10%' comment. The rest is smooth sided. Yes, removing the paint might marginally improve heat transfer but your 10% argument is 'just plain silly'. The heat sink should be pushed further down on the filter.
Upgrading the fans? Do you mean increasing the speed to eliminate laminar flow? If so, that is a viable option; however, along with that increase in speed comes increased noise, which is a common complaint with the present fans. Jtakeman presents the most important area for improvement, which hasn't been attacked by manufacturers IN MOST CASES for decades. We still use smooth round tubes instead of finned, spiraled ones with much more surface area both inside and outside. We have the technology to extrude complex aluminum and brass shapes so why not use it?

 

[jtakeman]

most important area for improvement, which hasn't been attacked by manufacturers IN MOST CASES for decades. We still use smooth round tubes instead of finned, spiraled ones with much more surface area both inside and outside. We have the technology to extrude complex aluminum and brass shapes so why not use it?

Some have made their stoves with just a big open box and so little area for heat transfer its pathetic!! Anything to increase the area or help sink the heat into the heat exchanger has shown improvements. But what do we know, Were just dumb burners!!

I remember this fella adding springs inside the tubes of his quad.

 

[dlehneman]

I've always thought my PAH would do better with more fins to transfer heat. It is basically an "open" design with 6 heavy gauge still fins that start inside the stove and protrude into the air outlet . More fins might make cleaning slightly more difficult and add a few pounds to the stove but I would think it would be worthwhile. Maybe Mike has some insight on that?

 

[Deromax]

Yeah, round tubes are steam locomotive era tech. It's incredible that such basic heat exchangers are still used on upscale stoves. A chunk of extruded aluminum fins would add maybe 10$ to the cost of a stove. If they are on the air side, they would not clog with ash and combustion byproducts.

 

[pell it]

I made these and put them in the exchanger tubes. I will compare to last years numbers once we get burning here.

 

[sportbikerider78]

You must not be familiar with an oil filter because only the very end of the filter has the 'scallops' to engage the filter removal tool, hence the '10%' comment. The rest is smooth sided. Yes, removing the paint might marginally improve heat transfer but your 10% argument is 'just plain silly'. The heat sink should be pushed further down on the filter.
Upgrading the fans? Do you mean increasing the speed to eliminate laminar flow? If so, that is a viable option; however, along with that increase in speed comes increased noise, which is a common complaint with the present fans. Jtakeman presents the most important area for improvement, which hasn't been attacked by manufacturers IN MOST CASES for decades. We still use smooth round tubes instead of finned, spiraled ones with much more surface area both inside and outside. We have the technology to extrude complex aluminum and brass shapes so why not use it?

I looked at the picture of the automotive style oil filter. Looks standard to me,,,,i've only spun about 200 of them in my life, but I know how they work and how they are shaped. My point was that conduction heat is almost zero,, so whats the point of a conduction heat sink?

It is true, that increasing speed usually means increasing noise, but not always. Fans are getting quieter and better. Or I wonder if a removable insert inside the heat exchanger tubes would be more effective. hmmmm...
(edit,,,,just saw the above posts...cool idea)

 

[Dragonfly]

I am already getting some condensation on my OAK flexible pipe at 28 degrees outside air temp. My OAK is about 1 foot from my exhaust which has about 8" before exiting through the thimble. I was thinking about wrapping the flexible OAK a couple of turns around the exhaust. This might keep the OAK conduit warm enough to cut down on the condensation (which will only get worse as real winter sets in) and warm up the outside air a tad. Has anyone done this? Any reasons not to try this?

 

[DMKNLD]

Pro5oh, tj, jtakeman, et al: I missed this thread when it first started up a month or so ago - thanks Dragonfly for bumping it back up to the current thread topics.

And I clearly didn't have enough coffee this morning to get my brain wrapped around this amazing discsussion on the thermo-kinetics of heat exchange, and the 'hinkering for tinkering' that motivates and innovates you guys to take pellet stove burn efficiency to a whole other level.

Coming from a guy whose pellet stove MRA (mechanical reasoning ability) when I first found this most excellent forum was pretty much limited to "you put the pellets in the top of the stove and you take the ash out of the bottom of the stove", I am continually amazed and impressed with the scope and breadth of knowledge of this forum membership.

Time for more coffee to think about all this ........ and go put pellets in the top part and take the ash out of the bottom part !