Not getting Secondary burn with EPA caddy

[Unethical Sloth]

I have some questions about getting the secondary burn with my Wood caddy (UH-caddy model I believe). I am new to heating with wood, I purchased this home in may and this is our first winter. The home has a caddy wood/oil furnace. I have been burning seasoned maple wood for about a month now and noticed that the furnace struggles with -20c temps. I try to keep the house around 21c (71f) to do this the furnace keeps the damper fully open at all times. The house is fairly well insulated (built in 2008) and when I use the heat pumps (when its warmer than -5) they barely even run and the house stays warm.

When the damper is fully open the flames just roar out towards the baffle and don't pass through the air tubes at the top. I see some secondary burn when the damper closes but its very minimal yet I see videos on youtube where people get a ton of secondary burn. I have a hugely long chimney that I suspect overdrafts but I am curious if anyone else has a caddy and knows more about the subject. Can draft affect proper operation? what kind of wood consumption is to be expected?

 

[ManitobaSky]

You will have better luck with this question in the boiler and furnace forum.
Update:
Thank you whoever moved this for the OP, hopefully they can get some help a bit faster now.

 

[sloeffle]

I've been burning a Caddy for about 10 years now, and I too struggled the first year or so getting it dialed in. With the help of some folks on this board I've been able to get it dialed in pretty well.

List of things below to check:

• Wet wood. What is your MC on freshly split piece of wood ?
  1. This is the culprit 75% of the time from my experience.
• Is the baffle board above the burn tubes pushed all of the way to the back ?
  1. I vacuum my burn tubes out a few times a year.
     1. Don't waste your time and taking them out to clean them.
• Is your heat exchanger clean ( the door on hinges above the loading door ) ?
• Any idea what your draft is ? It's suppose to be between .04 and .06.
• Chimney configuration ?

My standard procedure is to run the damper open for about 20 minutes or so to get the wood charred. After the wood is charred I keep a small nail between the damper and the stove to prop the damper open a bit afterwards. A paper clip works also.

 

[Unethical Sloth]

.The wood was seasoned sugar maple, at least one year, it looks pretty dry but I don't have any way of measuring humidity. The wood does feel pretty heavy but I just don't have enough experience to tell the difference.
. I have the baffle pushed snug towards the back per the user manual. I move it up every time I clean the heat exchanger. Which brings me to cleaning, I clean it once a week, there is a decent amount of fine ash in the heat exchangers, its certainly not creosote but still a decent amount.
.The chimney has two 45 degree elbows that go out from the basement, up the side of the building and about 3-4 feet above the roof. I am no good with numbers but its at least 35 feet.
. I wish I knew how to test draft, even if I had the tool I would not know where to place it. I feel like that is where my problem is as when the chimney is hot, the flames rocket up the baffle like they are getting vacuumed (i guess technically they are) and you can hear a slight howl. My thermostat controls the damper, so long as the thermostat calls for heat, the damper stays up.

 

[laynes69]

I agree with sloeffle on the wood. Seasoned wood is hard to get unless you can cut/split/stack and cover for 2 years (soft maple a year). Running with the damper open actually cools the furnace and heat exchanger. As mentioned, I would load the furnace and run the damper open for 10 to 15 minutes then close it. A nail or paper clip can be placed on the damper to keep it cracked open. Once the firebox is hot and the wood is charred, when the primary damper closes the temperature increases with seasoned wood. If the fire dies after charring and closing the damper, poor draft or wood is to blame.

 

[laynes69]

.The wood was seasoned sugar maple, at least one year, it looks pretty dry but I don't have any way of measuring humidity. The wood does feel pretty heavy but I just don't have enough experience to tell the difference.
. I have the baffle pushed snug towards the back per the user manual. I move it up every time I clean the heat exchanger. Which brings me to cleaning, I clean it once a week, there is a decent amount of fine ash in the heat exchangers, its certainly not creosote but still a decent amount.
.The chimney has two 45 degree elbows that go out from the basement, up the side of the building and about 3-4 feet above the roof. I am no good with numbers but its at least 35 feet.
. I wish I knew how to test draft, even if I had the tool I would not know where to place it. I feel like that is where my problem is as when the chimney is hot, the flames rocket up the baffle like they are getting vacuumed (i guess technically they are) and you can hear a slight howl. My thermostat controls the damper, so long as the thermostat calls for heat, the damper stays up.

You need a manometer to measure draft. Your post tells me your draft is too high not allowing the exchange of heat within the furnace. A Caddy will put out alot of heat!

 

[sloeffle]

I'm with @laynes69 on this one. If I was a betting man, I'd bet it's combination of wet wood and too much draft.

Do you have barometric damper on your chimey ? My chimney is a lot shorter than yours and I run one just to be safe because of the windy days we tend to get in the winter. I've seen a good wind gust pull the flap on my baro wide open and the draft is still over what it should be.

 

[Unethical Sloth]

I'm with @laynes69 on this one. If I was a betting man, I'd bet it's combination of wet wood and too much draft.

Do you have barometric damper on your chimey ? My chimney is a lot shorter than yours and I run one just to be safe because of the windy days we tend to get in the winter. I've seen a good wind gust pull the flap on my baro wide open and the draft is still over what it should be.

There is a small barometric damper on the oil chimney right before the connection with the main chimney. its mostly shut and I havent touched it as the user manual says to leave that to the techs.

 

[brenndatomu]

I'm with these guys ^ ^ ^, this sounds like "seasoned" (read: wet) wood...and high draft is a contributor too...but you need dry wood first.

 

[usernametaken]

A couple questions for the OP. Is your caddy the newer version that has the digital touch screen that controls fan speed based on plenum temp? Is the Caddy correctly sized to work with the sq/ft of your home? I have the larger Max Caddy version. Between my home's size, the amount of very tall windows I have, and the extensive duct network the heat needs to pass through to get to the second floor and room over the garage, my unit can barely keep up when it gets below 10F and the winds pick up for any significant amount of time. This is with wood under 10% MC and draft set to .05 too. My intake damper will stay open almost the whole time when temps are this low and despite what others above have said, the plenum temp on mine goes WAY down when the intake damper closes. That said, the lack of secondaries in your burn is different than mine. I get a raging fire from the wood load and also get nice secondaries rolling from the air tubes when the intake damper is open.

What I do agree with from the above posts is that moisture content and draft are likely a big part of the issue. To start, spend $30 on a moisture meter from Amazon. This one is popular: General Moisture Meter Then you need a manometer for your stove pipe to check draft. Most folks like the Dwyer liquid filled but I preferred this style. It's more expensive but a great gauge: Magnehelic

To use the moisture meter, you need to do a fresh split on a piece from your supply and insert the probes vertically or with the grain. Report back on your findings and I bet that will be the issue with your moisture content. To install the manometer, you simply need to drill a small hole in your stovepipe after it comes out of the furnace's collar. Insert a piece of 1/4" metal tubing in the hole and point it downstream. Once away from the heat, adapt that metal tubing to rubber 1/4" and connect it to the gauge. If you are over drafting, you'll need a barometric damper on a vertical section of your stovepipe. It needs to be as level as possible. Here is an example: Field Damper Once installed it will be a very simple process to dial back the draft. You simply loosen the adjustment knob and slide the weight forward until you get to between .04 and .06 on your gauge and tighten it back up. (If your wood is damp, keep it at .06 for this season to help get your temps up.)

Now, back to my first original question. If you have the digital control / variable blower speed and your wood is damp, your plenum temp will rarely get high enough to reach the higher blower speeds. Depending on your ductwork volume, if you're stuck on speed 1, you're getting hardly any heat at the end of your duct run. On my Max Caddy, I need to see a sustained plenum temp (shown on the home screen on the digital control) of over 140 to kick the blower speed up. If it's not moisture content keeping your plenum temp down and your blower speed low, it could be static pressure. My house has three zones. On very cold mornings when all 3 zones are calling for heat, static pressure is too low with the amount of air going through the furnace and no matter how hot the fire gets, I'll never get the plenum temp to rise enough to get me to the next blower speed. What I've found I have to do is shut off the first floor zone (which needs the least heat if I leave the cellar door open and allow the radiant heat to rise). Shutting off zone 1 will increase the static pressure enough to get the plenum temp up enough to get me to speed 6 and we are off to the races with the house recovering to comfortable temps.

One last question for you is how well are your ducts insulated? Are they all inside the conditioned house envelope? Mine for the second floor and room over the garage were in unconditioned space and while they were insulated by the HVAC installer, they needed more. Sprayfoam made a world of difference in retaining the heat in the ducts and keeping the air in the returns from dropping further.

You may not have all these issues. However, I know how each contributes because when I built my home in 2019 I did have each of these issues. Installing the manometer and baro damper were the quick easy thing to do right off the bat. Figuring out how to deal with static pressure on a zoned system took some time / trial and error. Lastly, by the following year, my wood was dry so the MC issue was gone. I still loose a few degrees when I get sustained single degree days/nights and wind but it's nothing like our first year here where it was a battle to stay comfortable. I hope these ideas help you narrow it down in your home. Report back what you've tried and how it worked out...

 

[Unethical Sloth]

Thanks usernametaken

I will Try your suggestions.

The model we have is a UH-caddy 2006 model. There isn't a lot of info on the model beyond that and the serial no. it is about 26' wide.

My home is 2200sq. but we have 9'+ ceillings from the basement to the 2 nd floor so I have a rather large volume of air to heat. The ducts all run through the basement and the middle of the house with the exception of the master bedroom where the ducts run through the garage. I figure that I loose some heat there but I don't really plan on insulating those as the radiant heat helps the garage from freezing and the 2nd floor is usually the same temp is every room.

 

[brenndatomu]

This is with wood under 10% MC and draft set to .05 too. My intake damper will stay open almost the whole time when temps are this low and despite what others above have said, the plenum temp on mine goes WAY down when the intake damper closes. That said, the lack of secondaries in your burn is different than mine. I get a raging fire from the wood load and also get nice secondaries rolling from the air tubes when the intake damper is open.

If he has high draft and wet wood then the supply temps will never get real high, no matter if damper open, or closed...open just heats the flue up real well, and makes the wood go away rapidly...as you well know I'm sure.
About the only way to get supply temps up with marginal wood is to load it full, let the damper open until the wood is charred and the fire is rippin, then shut the damper slowly (by hand) and then prop it open a lil with a nail or something...have to fiddle with it to find something just the right OD so the fire gets enough air to sustain the secondary flames...while this works, it will still never be nearly as good as a load of truly dry wood.

 

[usernametaken]

Absolutely and that's one of the points I was making as well (the part about damp wood).... as long as he doesn't have a static pressure issue on top of wet wood. You can burn toilet paper with a proper draft and still have lower plenum temps if there is too much air rushing through. This is why PSG told me that I could use their furnace with a zoned system but it would be more temperamental. When you have wood like mine with the draft set correctly, you'll get intense primary and secondaries and you can easily sustain 140-160 plenum temps... but the static pressure needs to be set correctly. This will keep the Caddy blower at speed 6 so plenty of velocity to reach the end of the duct runs. I do completely disagree on the statement that you need to shut the intake to get the plenum temp up. Burning marginal wood or the dirt floor dry stuff I have now, it burns MUCH hotter with the intake damper open. Period. That's why a Caddy that is controlled by a thermostat has the damper open when there is a call for heat.

 

[sloeffle]

Based off of the OP's previous comments I'm pretty sure he has a Caddy, and not a Max Caddy. My Caddy is the same width as what the OP said his furance is. I bought my furnace in 2008 or 2009 so we probably have the same furnace. I have the wood / oil / electric combo unit also because you had to buy that unit at that time if you wanted an intergrated blower. The unit doesn't have a computer or any way to change fan speeds without physically moving the wires around on the back of the motor. IMHO - it's a pretty crude unit compared to the Kuuma, HC, Caddy Advanced, or even the Max Caddy from that era. With some of the Tundra mods it is definitely a much better furnace to run.

For the OP, last year I had an issue with wet wood. I talked to a couple folks here and they recommeded gettings some biobricks to mix in with my wet wood to help get the secondaries going. I found it best if they were at the bottom of the load so they help get rid of some of the moisture from the cord wood. I'm still using them this year because I find they fit in places that you generally can't fit a piece of cord wood. They come in handy for over night burns when you want to pack the furnace as fulll as you can.

 

[JRHAWK9]

Burning marginal wood or the dirt floor dry stuff I have now, it burns MUCH hotter with the intake damper open. Period. That's why a Caddy that is controlled by a thermostat has the damper open when there is a call for heat.

I would agree. It would really suck if the call for heat opened the damper which in turn resulted in a DROP in supply temps.

This is indirectly how the Kuuma operates as well. Instead of a house thermostat calling for heat, there is a thermocouple inside the firebox measuring firebox temps where the gasification is taking place. When firebox temps fall below what you have set the targeted "call for heat" inside the firebox at (ranging from 1080° - 1,380° on pilot), the computer will open up the primary damper to raise the internal firebox temps to the targeted temp. The more heat output you need, the higher you turn the computer up and the higher the targeted firebox temps are that will be maintained. The higher firebox temps are maintained by feeding the fire more primary air. The net result is more heat to the house....but at the expense of losing more heat out the chimney and burning wood faster.

I also see the highest supply temps when my Kuuma opens the damper intermittently or has it open more at the back half of the burn. My lowest supply temps are when it's on pilot air for hours at a time. If I need higher supply temps when on pilot, I just turn the computer up......this will lead to the computer opening up the primary damper a bit more in order to maintain the higher targeted firebox temps. Now, it's obviously the most efficient when on pilot air, but I can provide graphs that show my supply temps being the highest at the very beginning of the burn (when loading on a bed of coals and excessive off-gassing is occurring) or near the back half of the burn when the damper is opening/closing and/or remaining open a bit longer. It will obviously reach a point in the coaling stage where the supply temps will start to roll off.

 

[usernametaken]

I would agree. It would really suck if the call for heat opened the damper which in turn resulted in a DROP in supply temps.

Wouldn't make much sense the other way around now would it... LOL 😝

 

[Unethical Sloth]

Based off of the OP's previous comments I'm pretty sure he has a Caddy, and not a Max Caddy.

You described exactly what I have. I do not have control over the blower other than to set it on summer mode with continual fan mode... which CANNOT be used for heating, (I learned the hard way). For heating, the blower only turns on when the plenum hits 150 (edited).

I have a slight update. I got a moisture meter on amazon but I am still waiting for it to come in. In the meantime I had a few small breakthroughs:

1. I noticed that the air intake in the basement was not capped and that almost all my fresh air was being sucked up there instead of the air vents that are spread around the house. This presents a unique problem as my basement is usually around 10c (50f) thus the air going through the plenum is cold to begin with. the solution was close it, there is already enough vents to supply the fresh air. The Caddy blower stays on longer as a result
2. I have been struggling with excessive charcoal buildup. The furnace burns away all the gasses leaving charcoal that does not heat enough. My initial solution was to rake the coals up to the front where they would get more air flow. However, having that mass of heat so close to the door and baffle messed up the air flow within the combustion chamber - too much air in the front, almost no airflow in the back, herein lies the bigger breakthrough: By raking the coals towards the sides of the chamber creating a valley, I lay my logs across creating a bridge. This allows air to flow under the logs towards the back of the chamber and pull the gasses up and across the secondary tubes. The result is twofold: Firstly the charcoal gets way more airflow and burns away instead of accumulating, Secondly the concentration of gasses and heat ignite the tubes producing the secondary burn that I was not getting previously. I am now getting the entire combustion chamber to burn instead of just getting flames in the front of the chamber. I will call this the ''C'' pattern. Before this, I could only ever get the blower to run for a few minutes at a time, it would constantly stop and go, even with the chamber full of wood. I am now able to get the blower to run without stopping for 15-20 minutes. We just had another-32c night and I was able to keep the house at 22c which is way warmer than previously.

My theory is that when I loaded the chamber with logs lengthwise, I was prohibiting the fresh air to reach the back and produce the C pattern. The wood in the back only burned thanks to the gasification process and which squeezed the gasses out, these gasses then only burned in the front of the chamber leaving heaps of black unburned charcoal. Anyway PSG does not mention any of this in the manuals, a bit disappointing that I had to find out through trial and error.

 

[brenndatomu]

For heating, the blower only turns on when the plenum hits 250

That's not right, at all!!
Your FLS (fan/limit switch) is set wrong, or faulty if this is happening! It should come on somewhere between 120-150*F (adjustable)
You are giving up a TON of heat to the house if the blower doesn't run until 250*! Plus, that is headed toward fire hazard territory...I'd have the high limit set at more like 200-210*

 

[usernametaken]

Brenn is sure right about that. Your plenum should NEVER reach 250. There is something very wrong and potentially dangerous there. On your excessive coaling issue. This is also a sign of wet(ish) wood.

 

[sloeffle]

I agree with both comments above, 250 is way too hot. I have mine set for 150 on and 110ish off. I actually mine set to kill the 24V side ( high limit ) of things at about 175ish. That's as close and I get the dial to the 150 side.

@Unethical Sloth - I agree, their older manuals are not very good on how to operate the furnace,

 

[Unethical Sloth]

Maybe I misread the manual but it says: The fan limit control setting may vary depending on the type of installation. The temperature setting “out of service” is preset at 110 F, the temperature setting “in service” at 150 F. and the high limit at 250 F at the factory. These settings should provide a proper operation for most installations

This is how mine is currently set. I guess I am confusing ''in service'' with ''high limit''.

There is little to no airflow towards the back of the chamber if I put the logs in wrong.

 

[brenndatomu]

Maybe I misread the manual but it says: The fan limit control setting may vary depending on the type of installation. The temperature setting “out of service” is preset at 110 F, the temperature setting “in service” at 150 F. and the high limit at 250 F at the factory. These settings should provide a proper operation for most installations

This is how mine is currently set. I guess I am confusing ''in service'' with ''high limit''.

There is little to no airflow towards the back of the chamber if I put the logs in wrong.

OOS means the blower shuts off....IS means it turns on (normal operation) when it goes to 250* "high limit" than means the switch turns off the 24V power to the furnace (shuts the intake damper if its open) and turns the blower on if its not already...usually wired to "high speed" on the blower motor too.

 

[brenndatomu]

Your FLS (fan control/limit switch) is not working properly...

 

[brenndatomu]

Or the low speed tap (or whichever speed its wired to) is bad...then it can only run on high once it hits the high limit...

 

[Unethical Sloth]

Or the low speed tap (or whichever speed its wired to) is bad...then it can only run on high once it hits the high limit...

So I think I was confused on the terms, it is indeed set to 110 off -150 service - 250 high limit.

However, the blower runs on high or not at all. It kicks in on high at 150. The lower speed only runs when you set it to summer mode.