# Drolet Tundra II /  Heapro



## jacksnipe (Feb 3, 2017)

OK Guys, for those that have the new models up & running, after the firebox has been up to temps how long does the blower stay running to heat your space. I'm referring to the new models have have the probe type sensor that determines the temp in the plenum.
 The new unit I purchased last April for our shop is not working worth a damn so far. The blower will not run more than one minute & then shuts off for 2-3 minutes... then repeats cycling. I have contacted SBI about this & they said you have wet wood, I told them I have been struggling with this & experimenting for most of this fall winter. I'm burning cut up pallet material to get the unit up to temp with a full firebox of wood, when up to temp I close the damper door which provide massive secondary flames for a while. I'm using a Honeywell thermostadt but the building never warms up if the blower won't stay running.
 I'm thinking a faulty probe in the plenum, SBI says I'm running a blower speed 2 since I'm using 6 of the 10 outlets with dampers to obtain a static pressure of .2 on the manometer. Note: I'm dumping the heat from the plenum without ducting with shutters installed in each startoff adapter. The plenum is not worm in the back where the probe is installed, but in the front left side it is very hot. I have a condor magnetic temp gauge 
 Attached to the HE door & it has reached 600+ but the blower still cycles.. I'm at a loss here to figure where to continue


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## sloeffle (Feb 3, 2017)

My Caddy has a fan limit switch that reads temperatures in the plenum and determines when to turn the blower on ( 150F ) and off ( 100F ).  Are the on / off temperatures adjustable like they are on the fan limit switch ? If so, I would start there. It is possible they are too close and the temperatures are too close together causing it to cycle. 

I sometimes have to use a small finishing nail to prop the damper open for an hour or so to keep my fire going after I load it up so that fan doesn't cycle.

Have you checked the moisture on the wood with a moisture meter ?

What kind of flue ( 6" SS / 8 x 8 clay tile / etc ) is the furnace tied into ? And what kind of readings ( page 5 ) are you getting with a manometer on your chimney draft ?


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## jacksnipe (Feb 3, 2017)

jacksnipe said:


> OK Guys, for those that have the new models up & running, after the firebox has been up to temps how long does the blower stay running to heat your space. I'm referring to the new models have have the probe type sensor that determines the temp in the plenum.
> The new unit I purchased last April for our shop is not working worth a damn so far. The blower will not run more than one minute & then shuts off for 2-3 minutes... then repeats cycling. I have contacted SBI about this & they said you have wet wood, I told them I have been struggling with this & experimenting for most of this fall winter. I'm burning cut up pallet material to get the unit up to temp with a full firebox of wood, when up to temp I close the damper door which provide massive secondary flames for a while. I'm using a Honeywell thermostadt but the building never warms up if the blower won't stay running.
> I'm thinking a faulty probe in the plenum, SBI says I'm running a blower speed 2 since I'm using 6 of the 10 outlets with dampers to obtain a static pressure of .2 on the manometer. Note: I'm dumping the heat from the plenum without ducting with shutters installed in each startoff adapter. The plenum is not worm in the back where the probe is installed, but in the front left side it is very hot. I have a condor magnetic temp gauge
> Attached to the HE door & it has reached 600+ but the blower still cycles.. I'm at a loss here to figure where to continue





sloeffle said:


> My Caddy has a fan limit switch that reads temperatures in the plenum and determines when to turn the blower on ( 150F ) and off ( 100F ).  Are the on / off temperatures adjustable like they are on the fan limit switch ? If so, I would start there. It is possible they are too close and the temperatures are too close together causing it to cycle.
> 
> I sometimes have to use a small finishing nail to prop the damper open for an hour or so to keep my fire going after I load it up so that fan doesn't cycle.
> 
> ...


   I have not checked the static pressure in the 6" double wall 15' tall yet. Dry Pallet wood is being used for testing. The Heatpro doesn't have an adjustable fan limit switch. The fan comes on at approx 115 & shuts off at 140. I believe the set chimney is within spec. The ceiling height is 10'6" with a sq. Ft of the shop at 1900. It is quite cold in the shop
At 25 degrees at this time of the year, when the blower comes on it is sucking so much cold cold through the filter into the heat exchanger. It is cooling off the probe quite fast.
 One item I would like to point out, I went into the Max Caddy website & looked at the owners manual for the probe location vs the location on the Heatpro.... surprise they are mounted different. The same for the New Tundra II . They are both mounted on the side of the plenum, instead of at the rear.


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## sloeffle (Feb 3, 2017)

jacksnipe said:


> when the blower comes on it is sucking so much cold cold through the filter into the heat exchanger. It is cooling off the probe quite fast.


I think you hit the nail on the head.

Have you tried fabbing up a make shift return air box, so air is not getting pulled from the floor ?

If you look at the the big tundra thread you will see some posts from people that noticed better performance from the furnace when they started pulling return air from the ceiling of their basement. My wood furnace has always been tied into my return so I have never had that issue.

@brenndatomu, @3fordasho, @DoubleB @STIHLY DAN @JRHAWK9 any other ideas.


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## DoubleB (Feb 3, 2017)

Sloeffle mentioned exactly the first thought I had too.  @jacksnipe , do I understand correctly that you are heating a space that starts off at 25 deg F?  If so, that's essentially like changing the fan on/off settings to at least 190F/155F for a furnace installed in a house (since a house space is typically at least 40F warmer than your setting).

Heck, I can definitely notice the blower stays running longer when it cycles at the end of a burn cycle during the day when the house is warm (>70F), and the blower doesn't stay running as long in the early morning when I'm waking up and the house is cooler (~63F).  So I image that's probably what's happening for you.

If you start a burn cycle and the shop is 25F, what is the temp after a few hours?  For our houses, the Tundras (admittedly smaller) raise the temps 2-5 deg F after a few hours.  Your shop (1900 sq ft and 10' ceilings) is comparable volume to a house.  Plus, you probably have concrete floors which don't heat quickly.  So it wouldn't surprise me if after a few hours you've raised the temp from 25F to 30F, and your Heatpro worked just fine but it's still really cold so you couldn't tell a difference.

Does any of that sound like it fits your situation?


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## 3fordasho (Feb 3, 2017)

I'm running an Tundra in a 2400 sq ft quonset style building, the peak is 20ft and the inside is open to the peak. Spray foamed but plenty of leaks around the foundation and large overhead door.  These wood furnaces with 3.5-4.9 cuft boxes just don't have the firepower to quickly heat this type of volume but I've found the tundra can do a pretty good job of maintaining once up to my desired temp for working in the shop ~60F.
I run a 120k btu propane unit heater to get the temps up and then maintain with the tundra. Only takes about 10-15 mn run time on the propane unit.   Yes my Tundra cycled too much and pretty sure it was the low temps coming in the return.  I solved that by installing a Totaline head pressure control which varies blower speed depending on plenum temp, once that was installed and set up there is no or very minimal cycling.   FWIW I'm just a bit west of Mankato,MN for outside temp comparison.


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## brenndatomu (Feb 3, 2017)

jacksnipe said:


> I have contacted SBI about this & they said you have wet wood,


(First of all, confused by the title, do you have Tundra II, or a Heatpro? The HP is ~1/3 larger.)
I have to agree with SBI...you are having all the classic symptoms of wet wood. That pallet wood you have isn't necessarily _dry_, it is kiln dried just long enough to kill the bugs. Do you have any lumber scraps around? Commercially purchased lumber is kiln dried to _dry._ You could also try getting some ECO bricks to try out, throw a few in on top of a load of wood, see if things improve.
One thing I wonder, do you know what kind of air temps are actually coming out the vents? If you think the temp sensor is bad you will need to prove it.


jacksnipe said:


> The fan comes on at approx 115 & shuts off at 140.


Do you mean the other way around? On at 140 and off at 115? That's how it should be...

These units seem to do a lot better job of maintaining heat than they do raising the temp of a space more than a few degrees at a time. If I can keep the house temp at or above the tstat setting (and the damper closed) it will just sip wood and do a nice job keeping the house warm. On the other hand, if I get too far behind the tstat, it will struggle to get ahead.
The guys are right though, Sucking super cold air off the floor is costing you some BTU's for sure. 
For one thing, I would try is putting the blower on low speed (although I thought these things self adjusted the blower speed?) Do you have a filter on the blower cabinet...a lower speed and a good quality "HEPA" grade filter will slow the air down and give the blower some run time...it should run for an extended time non stop...many people get 2-4 hours (and more) run time after a new load on the T1. Your situation is a lil different though.

You do need to get an actual reading on your chimney draft though, nothing will work right if you don't have -0.04 to -0.06" WC draft. BTW, I can get a new Dwyer Mark II model 25 manometer shipped out to you for $35 if you need one.


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## jacksnipe (Feb 3, 2017)

DoubleB said:


> Sloeffle mentioned exactly the first thought I had too.  @jacksnipe , do I understand correctly that you are heating a space that starts off at 25 deg F?  If so, that's essentially like changing the fan on/off settings to at least 190F/155F for a furnace installed in a house (since a house space is typically at least 40F warmer than your setting).
> 
> Heck, I can definitely notice the blower stays running longer when it cycles at the end of a burn cycle during the day when the house is warm (>70F), and the blower doesn't stay running as long in the early morning when I'm waking up and the house is cooler (~63F).  So I image that's probably what's happening for you.
> 
> ...


  That sounds exactly what the situation is, the temp might raise 15 degrees or so


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## JRHAWK9 (Feb 3, 2017)

yeah, sucking in sub 60° air and trying to heat it will get you nowhere fast, especially with that volume of air you are trying to heat.  May not be the whole problem, but definitely a big part of it.


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## jacksnipe (Feb 3, 2017)

brenndatomu said:


> (First of all, confused by the title, do you have Tundra II, or a Heatpro? The HP is ~1/3 larger.)
> I have to agree with SBI...you are having all the classic symptoms of wet wood. That pallet wood you have isn't necessarily _dry_, it is kiln dried just long enough to kill the bugs. Do you have any lumber scraps around? Commercially purchased lumber is kiln dried to _dry._ You could also try getting some ECO bricks to try out, throw a few in on top of a load of wood, see if things improve.
> One thing I wonder, do you know what kind of air temps are actually coming out the vents? If you think the temp sensor is bad you will need to prove it.
> 
> ...


  It's a Heatpro, the serial # is 106 so it's one of the first made. Your right on the 140 on. 115 off, I have tried split oak firewood that measures 19% after it was re split & had the same results. I have not measured the air temp coming out of the startoff adapters, but the front left one is quite warm where the others are not very warm. I do indeed have the same manometer hooked up to the furnace plenum, but have not checked the double wall pipe coming off the furnace. It comes out the back into a tee & straight up to the ceiling then transitions into double wall sst through the roof for a total height of 15 - 16 ft.
  I don't think I can change the blower speed lower. I am using the cheap filter that came with the unit, I could buy a better quality filter but I think the blower will work harder then. It would be like running a dirty filter & increase static pressure.
  I was going to put in a large wood stove in the shop, but the insurance co. Said no. But a furnace was ok to install.


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## brenndatomu (Feb 4, 2017)

jacksnipe said:


> I could buy a better quality filter but I think the blower will work harder then.


Its actually just the opposite, a "better" filter (or a dirty one) puts _less_ load on the blower motor...less amp draw...easy to see for yourself if you have a meter.


jacksnipe said:


> I don't think I can change the blower speed lower


I think you are right...it appears it is a self adjusting variable speed as I thought.


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## jacksnipe (Feb 4, 2017)

brenndatomu said:


> Its actually just the opposite, a "better" filter (or a dirty one) puts _less_ load on the blower motor...less amp draw...easy to see for yourself if you have a meter.
> 
> I think you are right...it appears it is a self adjusting variable speed as I thought.
> View attachment 194072


  One thought that has been on my mind lately, is re-locating the RTD probe to the front left side where it is much warmer. This would keep the blower running longer, I would have to lengthen the wires to mount it as it is in the rear. The worst that could happen if it fails to operate is buying a new probe unit from SBI. How do I determine what blower speed it is running at. I have used meters that measure rpm from the motor shaft ? 
 My neighbors have old school wood furnaces Daka etc. in their shops & they work great, when the blower stops it's time to add wood. The smoke dragon type don't have glass in the doors though, except Englands soon to be replaced
unit..


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## brenndatomu (Feb 4, 2017)

jacksnipe said:


> One thought that has been on my mind lately, is re-locating the RTD probe to the front left side where it is much warmer. This would keep the blower running longer, I would have to lengthen the wires to mount it as it is in the rear. The worst that could happen if it fails to operate is buying a new probe unit from SBI


Might be worth a try. I think the probe will work fine with extended wires...but I would try to use wire similar to what is there now...very well may be shielded signal wire...which is not hard to come by. Fortunately an RTD does not use the special wire like a thermocouple does...would be a little harder for the average person the extend.
As far as motor RPM, I don't think the exact RPM matters as much as good ole seat of the pants feel. If it seems like things are working good, then good enough. 
But If you want to see RPM just for FYI, and you have access to a non-contact tachometer, that would be the easiest way to see the motor RPM. We have a strobe type at work, very easy to use on almost any rotating assembly. Turn it on, adjust the strobe speed to where the assembly appears to be standing still, the meter shows the strobe speed in RPM, done!


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## STIHLY DAN (Feb 4, 2017)

Starting at 25* temps your unit is never going to work. They are not designed for that, if you keep it up to temp I bet you will be fine. To make it work you may have to bypass the fan switch. Just put a toggle in parallel of the temp switch. Let the fan run all the time till the shop warms up then switch back to auto.


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## brenndatomu (Feb 4, 2017)

STIHLY DAN said:


> To make it work you may have to bypass the fan switch. Just put a toggle in parallel of the temp switch.


There is no switch...RTD probe.
Dan does bring up a good point though, you could test the RTD and see if the resistance is rising or falling with increased temps, then wire (parallel as Dan said) in a switch and the appropriate resistor to make the blower run the speed you want. Could even use a potentiometer instead of a plain resistor, then you could dial in the blower speed as needed.


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## jacksnipe (Feb 5, 2017)

STIHLY DAN said:


> Starting at 25* temps your unit is never going to work. They are not designed for that, if you keep it up to temp I bet you will be fine. To make it work you may have to bypass the fan switch. Just put a toggle in parallel of the temp switch. Let the fan run all the time till the shop warms up then switch back to auto.


  Maybe the Drolet was the wrong type of furnace to use in this environment. What type of furnace would you recommend for such an application. Note: during all of my analysis I discovered that if I disconnect the RTD probe connector from the control box in the rear of the furnace, the blower will run flat out at high speed. It will run continuously, but an alarm beeps & the readout says to hot on the display. It would be fine to unplug the probe, but trying to slow down the blower without the alarm going off is the problem. If the blower speed could be turned down, maybe the alarm wouldn't trigger


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## brenndatomu (Feb 5, 2017)

Its alarming because it thinks the furnace is melting down. Obviously the RTD resistance goes down upon heating up. so if you plugged a potentiometer in to the plug, you could adjust it up/down and get the fan speed you want. You will need to measure the resistance of the RTD when it is cold to get a feel for its "span"


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## STIHLY DAN (Feb 5, 2017)

jacksnipe said:


> Maybe the Drolet was the wrong type of furnace to use in this environment. What type of furnace would you recommend for such an application. Note: during all of my analysis I discovered that if I disconnect the RTD probe connector from the control box in the rear of the furnace, the blower will run flat out at high speed. It will run continuously, but an alarm beeps & the readout says to hot on the display. It would be fine to unplug the probe, but trying to slow down the blower without the alarm going off is the problem. If the blower speed could be turned down, maybe the alarm wouldn't trigger



To be honest, I don't think any wood burning furnace would be good for this application. The freezing air is the killer, even oil and gas units are not meant for this. Old school units would work best as they can give a lot of heat in a short period of time, these gassifying units are limited to how fast they can burn.
In your situation where you have the install all set I would just pick up a 250,000 btu torpedo heater to preheat the shop. Start the torpedo heater and load your wood furnace, by the time the fire gets up to temp your shop should be preheated enough for the fan to run. I would still restrict the air though. Also through out the manual, it is no good for you as its not being used as intended.


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## brenndatomu (Mar 21, 2018)

Ever get things sorted out @jacksnipe ? If so, what do you think of the Heatpro  now?


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## 3fordasho (Mar 22, 2018)

Had a conversation with @jacksnipe in early Feb. '18  about adding the variable speed blower control so suspect he is still trying to fine tune.


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## jacksnipe (Mar 22, 2018)

3fordasho said:


> Had a conversation with @jacksnipe in early Feb. '18  about adding the variable speed blower control so suspect he is still trying to fine tune.


 Well guys, we haven't started any updates yet. I have saved all of the info concerning the blower mods & hookup details. I did purchase a duct return for the blower that reaches the ceiling to pull warm air into the blower housing
Instead of off the cold floor. I also picked up an IR gun to check the rpm of the blower for reference. I monitor this website daily & have year round to pick up any new tips from other owners of the new type II drolet or heatpro models.
 It's been to much to cold in NW WI. To fool around with this stuff, I'm hoping to get started in April..


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## Highbeam (Mar 22, 2018)

I use a modern “gasifier” woodstove with a big blower and adjustable snap disk to heat my shop that is often very cold.

Sure, the blower draws very cold air and causes the blower to cycle more often but the appliance is still heating the space.

I think it is misleading to say that these furnaces are only good at keeping hot spaces hot. Instead, just acknowledge that when the room temp is very cold that it will operate differently than when the room temps are hot. Probably less efficient but certainly a heat source. Maybe more efficient since cold return air is denser and more able to strip heat from the furnace.


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## JRHAWK9 (Mar 22, 2018)

Highbeam said:


> Maybe more efficient since cold return air is denser and more able to strip heat from the furnace.



I would be concerned about condensation forming inside the firebox with that cold air against a hot firebox.


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## Highbeam (Mar 22, 2018)

JRHAWK9 said:


> I would be concerned about condensation forming inside the firebox with that cold air against a hot firebox.



Starting a wood fire in a 40 degree stove, I get quite a bit of firebox condensation until the temperatures rise enough to support secondary combustion. Then you simply make sure that flue temperatures are high enough to prevent condensation. 

Every lb of fuel burned will release a fixed amount of heat whether the ambient temperatures are 25 or 70.

These furnaces use insulated fire boxes and strip heat from the flue gasses mostly. You can only strip so much heat before the snap disc shuts off the blower and allows flue temperatures to recover.


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## JRHAWK9 (Mar 22, 2018)

Highbeam said:


> Starting a wood fire in a 40 degree stove, I get quite a bit of firebox condensation until the temperatures rise enough to support secondary combustion. Then you simply make sure that flue temperatures are high enough to prevent condensation.
> 
> Every lb of fuel burned will release a fixed amount of heat whether the ambient temperatures are 25 or 70.
> 
> These furnaces use insulated fire boxes and strip heat from the flue gasses mostly. You can only strip so much heat before the snap disc shuts off the blower and allows flue temperatures to recover.



I wasn't referring to the moisture in the flue.  I was more referring to the cold metal firebox upon lighting a fire and the warm/moist air from the freshly started fire condensing on the cold metal firebox before the furnace body is up to temp.  I'm assuming there is a certain level of insulation (ceramic blanket) in between the firebrick and the firebox metal.  If moisture ever gets trapped in between this insulation and metal firebox I'm assuming there is going to be some level of rust happening.  The colder the fireboxes metal jacket is the higher the chances of water getting trapped and causing rust.  This would be my worry with pulling in very cold outside air and running it through the air jacket of a warm air furnace.


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## Highbeam (Mar 22, 2018)

JRHAWK9 said:


> I wasn't referring to the moisture in the flue.  I was more referring to the cold metal firebox upon lighting a fire and the warm/moist air from the freshly started fire condensing on the cold metal firebox before the furnace body is up to temp.  I'm assuming there is a certain level of insulation (ceramic blanket) in between the firebrick and the firebox metal.  If moisture ever gets trapped in between this insulation and metal firebox I'm assuming there is going to be some level of rust happening.  The colder the fireboxes metal jacket is the higher the chances of water getting trapped and causing rust.  This would be my worry with pulling in very cold outside air and running it through the air jacket of a warm air furnace.



Maybe. Does anybody have fiber insulation between the firebricks and firebox steel? Even if this were the case it gets mighty hot at the actual firebox. 

Fire is at over 1000 degrees. The ambient air at 25 vs 65 is just not important to the firebox but I do believe it will cool the heat exchanger quicker. Enough to cycle the blower.


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## brenndatomu (Mar 22, 2018)

Highbeam said:


> Does anybody have fiber insulation between the firebricks and firebox steel?


Tundra 1 does...


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## Highbeam (Mar 22, 2018)

I feel like you’re imagining a wood boiler with perpetually 33 degree water jacket around the firebox. A warm air furnace is not like that. The still air around the firebox will quickly warm until it’s hot enough to be whisked away by the blower. Cold air is much less able to steal heat from the firebox than water. Imagine quenching a hot piece of metal in a bucket of water compared to waving it around in the air.


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## JRHAWK9 (Mar 23, 2018)

I could very well be wrong, but it's a concern I would have for sure.  Doesn't take much moisture at all to get trapped and to start the rusting process.  Once it starts, it's over with.

I would definitely make sure my low limit snap switch was set appropriately to keep the temps up inside the air jacket as much as possible.


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## maple1 (Mar 23, 2018)

I don't think I would be too concerned. It's an issue with boilers but they have liquid cooled fire boxes.


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## AnthonySr (Apr 21, 2018)

jacksnipe said:


> Well guys, we haven't started any updates yet. I have saved all of the info concerning the blower mods & hookup details. I did purchase a duct return for the blower that reaches the ceiling to pull warm air into the blower housing
> Instead of off the cold floor. I also picked up an IR gun to check the rpm of the blower for reference. I monitor this website daily & have year round to pick up any new tips from other owners of the new type II drolet or heatpro models.
> It's been to much to cold in NW WI. To fool around with this stuff, I'm hoping to get started in April..


Jack snipe did you ever figure out a solution I seem to have the same problem


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## jacksnipe (Apr 23, 2018)

AnthonySr said:


> Jack snipe did you ever figure out a solution I seem to have the same problem


 Nope not yet, I'm getting ready to start in next week hooking up the cold air return to the blower box. I'm installing ducting at the ceiling level to pull warm air into the blower housing, instead of drawing cold air off the floor. I had to fashion up a sheet metal part the fits outside the furnace filter. The weather is starting to warm up so the results won't
Be fully determined until this fall. The next step if req'd is to mount a fan control for the blower. I'm thinking the hook up
Might be seat of the pants, but the diagrams that were supplied by the forum members provide some important details. Note: The Heatpro wiring is a bit different than the tundra because of the probe in the plenum..


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## AnthonySr (Apr 27, 2018)

It was about 40 today and the only way I can get it to blow real high is to have the damper open and feed it huge amounts of wood. Have you tried there technical hot line?

I am considering building walls around it and having the ducts go through the wall
to preheat the air before it gets to the unit any thoughts?

Anthony


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## AnthonySr (Apr 28, 2018)

AnthonySr said:


> It was about 40 today and the only way I can get it to blow real high is to have the damper open and feed it huge amounts of wood. Have you tried there technical hot line?
> 
> I am considering building walls around it and having the ducts go through the wall
> to preheat the air before it gets to the unit any thoughts?
> ...



I think we figured it out but it took a little cheating. I took about a 12 inch piece of 6 inch duct
And scribed it to the exhaust flue off the back of the furnace on the horizontal on the top we sealed it off with a cap then we put a hole in it and stuck in the probe.

Until I figure a better way this seems to be working perfectly of course we are bringing the furnace temps down but my barn is warming up just fine. Can’t wait to try it next year in the cold weather.


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## JRHAWK9 (May 22, 2018)

Highbeam said:


> I feel like you’re imagining a wood boiler with perpetually 33 degree water jacket around the firebox. A warm air furnace is not like that. The still air around the firebox will quickly warm until it’s hot enough to be whisked away by the blower. Cold air is much less able to steal heat from the firebox than water. Imagine quenching a hot piece of metal in a bucket of water compared to waving it around in the air.




I see you posted in this thread "over there".  This is exactly what my concern would be when using the OP's furnace in such a cold area.  Not sure what his issue is or what caused it after 8 years (I think it was), but I can see it being exaggerated if he would have been trying to heat a building up from 25° all the time.  Man, that is some THIN metal used on those BK's.


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## Highbeam (May 23, 2018)

JRHAWK9 said:


> I see you posted in this thread "over there".  This is exactly what my concern would be when using the OP's furnace in such a cold area.  Not sure what his issue is or what caused it after 8 years (I think it was), but I can see it being exaggerated if he would have been trying to heat a building up from 25° all the time.  Man, that is some THIN metal used on those BK's.
> 
> View attachment 226866
> View attachment 226867



Unlike any current furnace, the bk firebox mostly runs very cold with no flames and intentional gooey tar coating everything since the firebox itself is below the condensation point. The cat stays hot and eats up the smoke to make heat. The steel should have been thicker to prevent rust through or maybe there was something else wrong there.

This is completely different than a noncat stove or furnace that runs firebox minimum  temperatures several times higher to maintain low emissions. 

I have a bk and that rust through concerned me.


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