Kuuma "nerds", I need your advice:

[RockyMtnGriz]

Hello Gentlemen, and the odd Gentlewoman.

There's a lot of folks who are far ahead of me in tinkering with the Kuuma Furnaces. I need your advice. I know things are thin around here in the summer, but I also think the people I need to hear from have alerts on this forum.

I really need to get my Kuuma to shut off when the draft control goes to "2" on a fading load of wood. Maybe it's my home, my softwood, or the long shoulder seasons (yeah, I'm firing mine tonight, strictly for DHW and not heat, for the first time this year, on 6/27), and my life would be so much better if I had a "coal holding" rather than a coal burning feature I could select at times.

I've expressed this to Kuuma numerous times, and I get that their hands are tied by what they went to certification with, so it ain't going to happen unless they get a lot of competitive pressure. I can't wait around for that - if it can even happen within CO standards.

I had a thought the other day that the right switch, installed in the right spot on the air inlet box, could be used to trip off the power on the computer when it hit "2", thus giving me a good pile of coals to work with 12 hours later. One quandry is was should I try to interrupt the power to the stepper motor on the airbox (convenient), or the computer itself. Some poking about tonight as the stove was doing it's thing, showed that I could poke the flap to whatever position, and it would stay there, but turning the computer off, resulted in it snapping shut. I'm wondering if there's a holding coil that holds the flap in whatever position as long as there's power to the stepper motor. If so, just opening the circuit with a switch would allow the flap to go shut, which is what I'm after, but I'm not yet sure that would work, and I'm not sure that's a good thing for the computer - opinions desired!

I'm early on thinking this through, but there's many of you who have done so much with these furnaces, if there's some "been there, done that", experience I can benefit from, I'd appreciate it! I realize that a software tweak is the cleanest way to do this, but I think a luddite mechanical solution is what I can reasonably accomplish, and it won't have unintended consequences that might leave me cold in the middle of next winter!

I also have a big, growing crack in my furnace from the ash door spreading to the corner, an issue that Kuuma says they're aware of and have a fix for, but if anyone has been there, I'd appreciate hearing your experiences.

 

[JRHAWK9]

@brenndatomu has done this to his when it goes to '3'. He's cutting the power to the computer by using a MYPIN temp controller.

I also have a big, growing crack in my furnace from the ash door spreading to the corner, an issue that Kuuma says they're aware of and have a fix for, but if anyone has been there, I'd appreciate hearing your experiences.

First I have heard of this.

 

[brenndatomu]

@brenndatomu has done this to his when it goes to '3'. He's cutting the power to the computer by using a MYPIN temp controller.



First I have heard of this.

Yeah I seen this earlier, but didn't have time to comment...still don't really, it gets kinda complicated, I'll circle back later today or tonight.
Same here on the crack...refurbed a number of them, haven't seen that one. This is external, right?

 

[sloeffle]

I'm sure brenndatomu's solution will be a lot more elegant than the below solution.

I have a IOT network at my house and use it for monitoring house temperatures, outside temperatures, turning switches off and on based off of various criteria. Since I'm a cheap a$$, I put a temperature sensor outside and have it shut off my water heater for my cattle during the winter when the temperature is above 32F. I actually have a sensor in one of my air ducts that I used for monitoring my wood furnace temps when I worked in an office.

Could you put a temperature sensor in the duct near the furnace that monitors the temperature and if it is X degrees for so long that it then kills the power to your furnace.

 

[RockyMtnGriz]

brenndatomu - Yes, "crack" is external just to the right of the ash door frame. They say it's rust from condensation. Not sure how that happens when the thing is warm at least 10 months of the year, and if you've spent time in the Rockies, you'll know that humidity is not a thing here. More like freezer burn. For instance, today the Weather Service is calling it a heatwave today. It's officially 76 outside, with 22% rh, and the weather station is right next to the lake, so the rh is a little suspect when the lake's not frozen. My rh sensor says 12% outside, and 43% inside, though it might read a little low. It's new and I haven't checked it yet.

I appreciate your help in advance! I'm not sure the mypin would work, since I would need a temperature signal that I don't have when the draft is stepping up to 2. The only signal I've seen that the wood has been consumed and just coals remain is the computer kicking the draft up to 2. Maybe I'm missing something, but I just don't want to waste your time on a complicated explanation if it won't help. Not that it probably wouldn't help someone else sometime if you choose to record it here.

sloeffle - I'm with you, no point heating water above 32. That's like setting dollar bills on fire.
I've monitored this thing a lot with a Fireboard, and I don't see any useful temperature signals. As I was getting at above, when I need it to turn off, it's pretty much at normal operating temp, it's just running flat out to do it, burning up all the coals that I'd sometimes rather keep for a while.

 

[JRHAWK9]

I'm not sure the mypin would work, since I would need a temperature signal that I don't have when the draft is stepping up to 2.

You use the OEM thermocouple. When the computer is set on minimum burn, here are the approximate temps at which the damper does:

'C' to '3': ~160°
'3' to '2': ~825°
'2' to '1': ~930°
'1' to 'c': ~1,080°

The higher you turn the computer, the higher those temps are skewed. So you'd use the MYPIN to cut power when it reaches whatever temp works for you. Cutting it too early may lead to creosote buildup though. I believe bren has it cutting power around the 700° area, but I could be wrong.

I'm using a temp controller to simply monitor firebox temps.

 

[RockyMtnGriz]

Yes, I was missing something! Pulling the temp from the thermocouple would be ideal.

I look forward to the details!

 

[brenndatomu]

I appreciate your help in advance! I'm not sure the mypin would work, since I would need a temperature signal that I don't have when the draft is stepping up to 2. The only signal I've seen that the wood has been consumed and just coals remain is the computer kicking the draft up to 2. Maybe I'm missing something, but I just don't want to waste your time on a complicated explanation if it won't help. Not that it probably wouldn't help someone else sometime if you choose to record it here.

So I've been mulling this over all day...what to share and what not to...not that I don't want to help, because I do enjoy helping people make their stuff work better for them. My hesitation is in helping people modify equipment that can cause fires, and could hurt someone if things go wrong...also insurance companies can use any little excuse to not cover a claim..."oh, this wiring doesn't look factory Mr Griz"...UH OH!
I was a lot less hesitant before, but after helping a lot of people make what I thought were some pretty simple mods on a popular wood furnace model that I owned previously, and then later on seeing the results of some of that "workmanship" in pictures, it kinda made me realize that some people don't even know which end of a screwdriver to use as a hammer, let alone wire up controls!

Now, that said, maybe you could just do as was first suggested to me by Mr Lamppa himself...just shut the computer off once it goes to "3"...(more on this later) you can even use (2) 3 way switches so that it can be shut off upstairs, and turned back on downstairs. If you were to do it this way you almost need a way to remotely monitor the temps...a remote wireless BBQ thermometer works pretty darn well for me...I monitor the supply plenum temp, and the internal flue temp, about a foot out of the furnace...once you get the feel for what normal temps look like when the computer goes to "3" at the end of the load, you will know when to flip the switch...you could even get a temp monitor with wifi and have it record a trend chart on your computer...or be able to shut it off remotely from your cell phone (with a wifi switch) And speaking of switch, in my opinion the best place to kill the power is the 24VAC coming into the computer, just shut it down...that way the blower controls still work and you don't have to worry about any weird voltage spikes or anything.
I know I've heard that there is a customer of Lamppa's that is a computer guy and he has his VF all wired up to a PC with tons of his own controls and custom monitoring...don't know details of how it was done though...somebody with skills and knowledge well beyond my own, at least when it comes to computers and controls! And I'm sure there is other/better ways of doing what I did too...I know just enough about electronics and controls to get what I need to do at work done. (which is still more than I'm actually required/expected to do)

Ok, back to the whole shutting off at "2" or "3" thing...Daryl explained to me that when the computer is doing the whole "c-1-c-1" thing, the firebox is in gasification mode...once it starts with "1-2-1-2" it is starting to burn off some cellulose, and even more so when you hit "2-3-2-3"...but by the time it starts to be on "3" more that not, at that point it is pretty much just burning down coals, and shutting off the computer at that point will not cause creosote...sounds like doing it much earlier than that could...and additionally I would worry about cutting it too early, snuffing the fire and risk getting a huge "puffback" from smoke (fuel) buildup in the firebox/chimney...or stall your chimney and cause CO issues in the house...but this could happen even if you wait until "3"...so you really need to be sure you know your chimney and have working CO detectors! Chimneys don't act the same in warmer weather (like you describe) as they do in proper winter weather.

Some poking about tonight as the stove was doing it's thing, showed that I could poke the flap to whatever position, and it would stay there, but turning the computer off, resulted in it snapping shut. I'm wondering if there's a holding coil that holds the flap in whatever position as long as there's power to the stepper motor. If so, just opening the circuit with a switch would allow the flap to go shut, which is what I'm after, but I'm not yet sure that would work, and I'm not sure that's a good thing for the computer

Yeah, there is a coil...the stepper motor...and you are just overpowering it, forcing it into the next segment...I wouldn't do this. I had to replace a motor on one that I refurbed, it wasn't even strong enough to reliably hold the flapper in the position that it was supposed to be...the computer would call for it to go from "3" to "2" and it would slip past...causes lots of problems! (it was just old and worn out)

I realize that a software tweak is the cleanest way to do this, but I think a luddite mechanical solution is what I can reasonably accomplish, and it won't have unintended consequences that might leave me cold in the middle of next winter!

Yeah, it really would be...but good luck find a way to do that...people that could, won't, due to liability, and the rest of us really shouldn't try!
Yes, last I checked, and new computer board was $400...and only one place to get them...and I would assume that they are having the same chip shortages that everybody else is....that price was pre CV19 too...price is probably double that now.

Ok...so getting down to it...yes, I tied into the TC with my temp controller to shut the computer off at XXX degrees...BUT, it did NOT come easily, or reliably! I bought 4 different (5?) temp controllers to find one that worked...and the cheapest POS I have is the only one that did the job...but it also only read the temp in Celsius too...argh!
The issue is that the mV that the TC makes does NOT like to be screwed with...the whole circuit is a "system", the TC, the TC wiring, the computer, and something as simple as tying in a temp controller really disrupts things...I talked with a bunch of people about what I was doing, and why one controller worked, the rest didn't...when I had the others hooked up, it caused some really weird problems with the computer...I stopped experimenting before I let the smoke out of something expensive. Anyways, the expert electronics people that I talked with said you can't do that, it just won't work...not satisfied with that vague answer I talked with the head instrumentation guy at work and he said kinda the same thing...when I asked why it seemingly worked fine with the one controller, he said, yeah, you might luck out and make it work eventually, but it is not something that any engineer would sign off on, and we would never use something like that in a professional industrial situation (lawyers would hand your azz to you if something happened and they found out about your lil rogue mod)
Now if you are still dead set on doing this, I'd really recommend installing a second separate TC to feed your temp controller...it will have to be something similar to what is use OEM, as lesser units just won't take the heat long term.
And to make it all work, you'll also need to wire in a timer to override the temp controller while the firebox is coming up to temp...I used a simple spring wound bath fan timer, also wired in a switch to select "normal" mode (OEM) or temp override mode (shut off at XXX temp...I picked 400*C)

Pulling the temp from the thermocouple would be ideal.

Seems that way at first, but its really not...and I wasted A LOT of time (and too much money) trying to prove otherwise. Now, if there is someone out there that knows something about all this that would prove me and all the experts I talked to (including the techs at Auber) about it wrong, please enlighten us! Always open to learning new things!

 

[brenndatomu]

And as far as the ash pan door area...so this is rust, or a crack? I would be shocked to hear about that area cracking...even rusting would be a real surprise, at least in that area...but when they talk about condensation, I think it is more likely occurring during operation (not during storage/un-use) but again, I don't understand how that could happen in that spot...now if it was in the back of the firebox...you have cool air being blown on a warm surface (beginning and end of a load) and I think with just the right (wrong) humidity conditions you might could get some condensation at times...

 

[JRHAWK9]

BUT, it did NOT come easily, or reliably! I bought 4 different (5?) temp controllers to find one that worked...and the cheapest POS I have is the only one that did the job.

I forgot about this. I also had an issue. The original temp controller I bought caused the computer to go completely wacko, when tied into the OEM TC. I then bought a cheap MYPIN and it's been working for a few years now.

 

[RockyMtnGriz]

And as far as the ash pan door area...so this is rust, or a crack? I would be shocked to hear about that area cracking...even rusting would be a real surprise, at least in that area...but when they talk about condensation, I think it is more likely occurring during operation (not during storage/un-use) but again, I don't understand how that could happen in that spot...now if it was in the back of the firebox...you have cool air being blown on a warm surface (beginning and end of a load) and I think with just the right (wrong) humidity conditions you might could get some condensation at times...

So, there's a lot I don't get between what I think can reasonably happen in 3 winters, what I'm being told by Kuuma, and such. I don't have any interest in starting a bash Kuuma thread, or even one that takes on a second life with the Kuuma trolls. I think they're good people. I have confidence that one way or another, it'll get taken care of, and I don't mind sharing how it works out, because the truth should be shared. It's just that I have my opinions, they have theirs, which are a little different, and right now, I can't swear mine are correct.

If you, and Jrhawk9 and whomever else you want to vouch for (since I consider you both unofficial members of Kuuma's R&D team) want to join me in email for a confidential conversation, I'll start. My email (because I don't need it webcrawled) is as follows. The last letter of the alphabet, followed by "ugg", and ending with the first letter in Mary, at yahoo. I figure you guys probably already have each other's email, so my thought is to send an email to both (or more), so it can be reply all after that. You can look at the pictures, hear the details, and decide for yourselves. If you email me and don't want your email shared this way, please let me know, and I won't.

 

[RockyMtnGriz]

Brenndatomu, thank you!! That's exactly the info I came here for, and I appreciate your work in laying it out for me!

This is going to be long, so if you want the phone length version, I'm going to go with what I think is a fairly simple mechanical solution, since you've convinced me that the tech-based solution is far from simple.

And on with the long explanation:
To your first point, on giving people maybe more information than they should be provided with - I get it. I grew up in the Cascade logging woods 40+ years ago. Everybody I was around knew how to handle a chainsaw. I came to think it was a universal basic skill. These days and living slightly elsewhere, I find that everybody I'm around says they can handle a chainsaw, but after a few scary experiences, when I assumed that they either could, or would have the smarts to say they weren't qualified for the job at hand, I've concluded that some definitely can't, and worse, most of them don't know that! Same deal with off-road driving, winter driving, etc. Salesman said they could do "anything" as long as they bought this (4wd or AWD whatever), and they believed it. I've since learned to have them demonstrate first, using their equipment, while I stay at a safe distance!

I've always said, the most dangerous items in the hardware store are the chainsaws, but (at least in some places) it's the pistols you have to get a license and training to buy. Never made sense to me!

Regarding turning off the computer when it reaches "3", as recommended by Kuuma, that's exactly what I want to do, I just want to do it automatically, because often the optimum time for that might be about 3,4, or 5 am, and I prefer not to have to monitor and perform that task at that time of the day. Or maybe I prefer to burn a partial load during a day I'll be away, and still not have the furnace dead when I get back. I think Kuuma really missed on a coal holding feature, or maybe they just couldn't do it and meet CO issues, but regardless, they're locked in with their test now, and I expect somebody to will be able to beat them up in this regard.

I also believe that the draft stays open way too long after the coals are gone, just cooling everything from my house it's drawing it through, to the stove, and the flue it's going up. Again, I can deal with that manually, but I'd prefer not to.

I'll preface my solution with an important point that my furnace apparently doesn't burn like yours, nor like Kuuma says it does. I think it's the softwood I burn. I can do a normal reload on a bit of coals, and in literally a few minutes, it'll go from roaring to C. On a lower setting, which is 95%+ of what I use, it'll cycle back and forth between C and 1, the vast majority of the time on C. Only when the load is nearly consumed does it bump to 2, never goes back to 1, and shortly thereafter (maybe even 10-20 minutes), it goes to 3 and stays there. So my plan may not work for somebody burning hardwoods, but I'm confident it'll work for me. I'd only have use for the coal holding feature when I'm burning at minimum settings, so the draft flap needing to be at 2 or 3 during the burn is not an issue for me, except for a few minutes right after I load the stove, when I'm usually gathering up and organizing my next load anyway. All I'd have to do is arm it after I hear the tink! of the draft closing.

I have a couple of Fireboard probes I've been moving around this furnace for the past year, but I have yet to see a temp signal that corresponds to the point where I would want to turn this thing off. At least one that I could automate with a simple "if this, then that". I'm also not in a rush to drill another thermocouple into the combustion chamber.

So the tech solution is far from simple, it appears. I think the mechanical solution is going to be far simpler. I have a flapper on the draft control that responds to the thermocouple signal that I'd be happy to use, but am not going to screw with based on your sage advice. All I need for the mechanical solution is an appropriate switch that can be triggered by the flap going to 3, or 2 if I choose. 2 is better for holding a larger load of coals, but probably more difficult to implement. A switch that would trigger every time the draft went to 3 seems pretty simple. Either the switch or a relay needs to latch in the off position until reset. I need a toggle switch with a circuit to bypass the interrupting switch or relay to allow the fire to start, or when I would prefer the stove to burn coals down, instead of preserving them.

The sensing switch at the draft box could be as simple as a copper strip that gets bumped into another copper strip when the flap opens to 3, completing a circuit and tripping a latching relay that opens the 24v to the computer. Tripping at 2, yet allowing for 3 when the bypass switch is set for coal burning might be a little trickier to design, but we'll see.

Simply providing a contact that would "ground out" a sensing circuit when touched by the flap could also work, if I could find a sensing circuit with a low enough current to be comfortable feeding it into the draft flap. And, I'd have to ponder what current I'd be comfortable with!

As for cautions about CO and creosote, while I'm not totally happy with the pipe and heat exchanger deposits, after a few years of experimenting, I'm sure the problem is not from the glowing BBQ coals that remain when my draft hits 2 on the lowest setting. I experimented with burning only on or above a 9 o' clock setting which helped, so then I reset the range control from factory to approximate the stock 9 o'clock at minimum. In addition to helping with the crudding up, it gave me a little more screwdriver-free headroom for the cold times. I have seen some evidence that preserving coals that keep everything warm, and rev up instantly and cleanly, helps maintain a cleaner heat exchanger and flue than the additional smoky cold-starts I'd have to do otherwise.

I'd like to be one of those guys who brags that they never have to clean the chimney on one of these, but so far, I don't see that coming.

I think the softwood I burn can at times produce more gas than the secondary can burn, especially with the secondary air volume crippled by 20% less air pressure at my altitude. I think that also factors into exhaust deposits. I do know that the furnace works better with one of the "nostrils" in the air control taped shut. Doing that has pretty much eliminated the occasional nuisance overtemp alarms I was getting. I'm not certain, but I think it might also be contributing to a somewhat cleaner exhaust section. I think it just gives the computer more leverage to reduce the amount of combustible gasses going into the secondary when it needs to.

As far as CO goes, the heat from the hundreds of pounds of stove, combined with 30' of Class A holds a solid draft for a day after the last coal is gone. It's not a concern in my case. Yeah, I've got detectors too. They sometimes freak out when I drive the car out of the garage, but they've never noticed one of my stoves, even though occasionally maybe they should have!

I really appreciate your sharing your knowledge and experience, especially with what didn't work so well! I'm going to tinker up a switch-based cutoff setup secure in the knowledge that there's not a simple, elegant electronic solution that I'm blind to.

I'll follow up with how it works out.

 

[brenndatomu]

All I need for the mechanical solution is an appropriate switch that can be triggered by the flap going to 3, or 2 if I choose. 2 is better for holding a larger load of coals, but probably more difficult to implement.

Just to be excessively clear, I would really not recommend shutting things down when the damper is still on 2...there is still active fire at that point, more that just hot coals left...cutting the air could (very likely will) cause smoking, and all the problems that come with it.
I didn't set mine to shut off until well into "3" (as in, its been on 3 for a while now, none of the 2-3-2-3 stuff left)

 

[woodey]

Just for clarification to anyone who is researching for a wood furnace. Don't be confused by c-1-c-1-2-1 ...ect. That is a adjustment the computer makes to allow this furnace to be the most efficient, cleanest burning and easiest to operate on the market. Simply load the furnace, walk away and enjoy the heat.