Measuring the chimney draft on a pellet stove

[Brokk]

Just to see I had my youngest son came over with his Gauge .
He is an HVAC tech here in Ontario. He tested my draft and found where I
have it set is higher than recommended. We adjusted it as close as it
would go to recommended ( really not even close with draft almost closed)
Flame very dirty black tips. So we adjusted the fire for its best burn
clean and efficient. That's all I ask for from my stove other than heat

I just ordered a rheostat and my wife talked me through how to hook it up. She's the one with the electrical engineering degree, who also happens to be in Ontario at the moment.

Meanwhile the mfg is suggesting the problem is that I don't have an OAK installed, ignoring the whole "wind tunnel in the fire pot" problem.

 

[Brokk]

I just ordered a rheostat and my wife talked me through how to hook it up. She's the one with the electrical engineering degree, who also happens to be in Ontario at the moment.

Meanwhile the mfg is suggesting the problem is that I don't have an OAK installed, ignoring the whole "wind tunnel in the fire pot" problem.

I tested out if the room pressure was the problem. I opened a window all the way. A nice breeze was trying to push into the room. The gauge moved, showing an increase in pressure. I opened the stove door and zero'd the gauge. Then I started the stove after closing the door. No difference. Still .40WC using room air.

 

[Clarkbug]

I just ordered a rheostat and my wife talked me through how to hook it up. She's the one with the electrical engineering degree, who also happens to be in Ontario at the moment.

Meanwhile the mfg is suggesting the problem is that I don't have an OAK installed, ignoring the whole "wind tunnel in the fire pot" problem.

Standard disclaimer about adjusting the fan speed impacts combustion and potentially does stuff that could cause it to spontaneously combust, etc.etc.

Having an OAK certainly wouldnt hurt, and I get why thats on their troubleshooting chart for people that have a very tight house. But I dont think thats going to impact you when you have that much chimney that is sucking on your stove.

 

[Brokk]

Standard disclaimer about adjusting the fan speed impacts combustion and potentially does stuff that could cause it to spontaneously combust, etc.etc.

Having an OAK certainly wouldnt hurt, and I get why thats on their troubleshooting chart for people that have a very tight house. But I dont think thats going to impact you when you have that much chimney that is sucking on your stove.

How the mfg wants me to test does not even get to the point of having a fire going. So they are leaving out any impact the chimney has. Basically they just want me to test their stove mechanics, but even when the values are way outside of their acceptable range, they have no suggestions for fixing the issue or even any attempt to explain why I'm getting way more vacuum than they say I should have.

A small adjustment via the variable resistor to the fan makes a huge difference to the vacuum. However the resistor near the contacts is getting unacceptably hot. This is OK for short testing periods, but I'm not sure it will work as a full time solution. Maybe a different resistor would be better.

 

[johneh]

What effect will the reduced draft have on the fire?

 

[Brokk]

What effect will the reduced draft have on the fire?

Ideally, make it more effective. Right now I'm going under the assumption that my draft is too strong, so it's moving the heat through the stove too quickly. I'm losing a lot of it up the chimney. If I can slow down the air flow in a more controlled fashion, then my stove can do a better job at heating the space it's in.

I read reviews of people with this same model stove heating uninsulated, drafty shop areas. Pulling up the temp from the mid-20s to near 80 after getting the stove up to temp. My setup takes me several hours to get my insulated living space from 50 to 65. So I'm chasing down every avenue of what could be going wrong. Where is all the heat going?

 

[Brokk]

How the mfg wants me to test does not even get to the point of having a fire going. So they are leaving out any impact the chimney has. Basically they just want me to test their stove mechanics, but even when the values are way outside of their acceptable range, they have no suggestions for fixing the issue or even any attempt to explain why I'm getting way more vacuum than they say I should have.

A small adjustment via the variable resistor to the fan makes a huge difference to the vacuum. However the resistor near the contacts is getting unacceptably hot. This is OK for short testing periods, but I'm not sure it will work as a full time solution. Maybe a different resistor would be better.

View attachment 283753

I'm returning this one and getting one that is meant for wood stove fans. This one just gets too hot (625F at 80V)

 

[Clarkbug]

I'm returning this one and getting one that is meant for wood stove fans. This one just gets too hot (625F at 80V)

Have you ever measured the flue temps to see if it's running hot?

 

[johneh]

Mine gets warm on most settings. I can hold my hand on the pipe(2wall)
up until it is on the highest setting then after a min or 2 I have to remove my hand
When I burn it on high the air temp at the output of the heat exchanger is better than 500
As far as temp at the chimney termination I don't think I will check it on the roof
Too old to be on the roof

 

[SidecarFlip]

Ideally, make it more effective. Right now I'm going under the assumption that my draft is too strong, so it's moving the heat through the stove too quickly. I'm losing a lot of it up the chimney. If I can slow down the air flow in a more controlled fashion, then my stove can do a better job at heating the space it's in.

I read reviews of people with this same model stove heating uninsulated, drafty shop areas. Pulling up the temp from the mid-20s to near 80 after getting the stove up to temp. My setup takes me several hours to get my insulated living space from 50 to 65. So I'm chasing down every avenue of what could be going wrong. Where is all the heat going?

Being a space heater and not a central furnace the heat is not going anywhere but where it's supposed to Only having 50K btu's to play with on high, don't expect it to heat your abode comfortably, because it won't.

I'm not following the excessive draft thing at all because the stove is a negative draft unit and will only put x amount of heat into the vent pipe and in your case flu.

 

[Brokk]

Have you ever measured the flue temps to see if it's running hot?

Actually I installed an inside thermometer (meant for double walled pipes) and when I ran it today it registered around 350F give or take. That was after about an hour of running. It was very slow to build up heat in the exhaust.

 

[Brokk]

Mine gets warm on most settings. I can hold my hand on the pipe(2wall)
up until it is on the highest setting then after a min or 2 I have to remove my hand
When I burn it on high the air temp at the output of the heat exchanger is better than 500
As far as temp at the chimney termination I don't think I will check it on the roof
Too old to be on the roof

You are saying the air coming out of the stove and into the room is 500F?!? How do you measure it? Meat thermometer?

 

[Brokk]

I'm returning this one and getting one that is meant for wood stove fans. This one just gets too hot (625F at 80V)

So the new fan control (rheostat) arrived. It was perfect. Two wires, nice and small, no crazy hot parts. It worked perfect. It could go from nearly 0 output to 100%. Once I got it hooked up and tested, I re-connected the pellet stove back to the flue and tried starting up the stove.

The exhaust fan is kind of strange. The fan trim setting does come into play during startup, I just hadn't let the stove run long enough. Initially it just goes full blast. Then after a few minutes, it allows the fan setting to temper the speed. Which is odd since the startup forces the feed rate for #4 (high). Once the stove finishes the startup process fully (igniter turns off), if it's on #4 feed rate, it then turns the exhaust fan on full speed and ignores the fan trim setting.

The fire box negative pressure is up over .5 during startup (depending on the fan trim setting) and it stays up there after startup. It was at this point I started playing with the new fan control I had hooked up. Until this point I left it on full, but now I started to turn it down and observe the negative pressure. I kept expecting the stove would go into shut down if I let the pressure get too low, but it never happened. I eventually turned the fan control all the way down to it's lowest setting (near 0) and if I had the air inlet open all the way, it dropped as low as .06WC. I let it run that way for a while, watching the fire burn rate and how the pellets behaved. Closing the air inlet all the way, cause the flames to stop being so straight and gave them some wiggle. They stayed yellow and no sign of smoke. Negative pressure at this point went to .15WC and stayed there. I'm pretty sure I could turn my exhaust fan off entirely and the draft from the chimney would keep things moving the same way.

When I shut the stove down, I played with the new fan control. With the air inlet still closed as far as it will go, if I turned up the control to 100%, the glowing pellets would start jiggling around in the grate, like Mexican jumping beans. Turning it down about 1/2 way got them to stop, but still maintained a very healthy glow to them. At 100%, the negative pressure returned to over .5WC

 

[johneh]

Your flame looks lazy . Watch this video I know it is not
your stove but it is the best I have seen

Pellet Stove Flame (Pellet Stove Proper Flame)

Looking at the flame of a pellet stove (pellet stove flame) can be an early indication as to whether or not your pellet appliance is operating properly.

friendlyfires.ca

 

[SidecarFlip]

Do keep in mind that an overly active flame (too much combustion air) will also cause hard carbon buildup on the firepot and close off the air passages drilled / punched into it.

 

[Brokk]

Your flame looks lazy . Watch this video I know it is not
your stove but it is the best I have seen

Pellet Stove Flame (Pellet Stove Proper Flame)

Looking at the flame of a pellet stove (pellet stove flame) can be an early indication as to whether or not your pellet appliance is operating properly.

friendlyfires.ca

It's hard to judge based on a single picture. The flames are always changing. While my auger turns like clockwork, the pellet feed seems almost random at times. Even on high I will sometimes reach a point of barely any flames, while other times the flames will be shooting high. The pellet supply impacts the flames immensely more than anything I do with the air flow. I'll try a short video next time to show.

In the mean time, I will say my flames are never as tall or wavy as low oxygen example. However, they are frequently short, bright and straight up like the too much oxygen example.

I bought some higher BTU softwood pellets this year. Perhaps that will help. I've tended towards hardwood in the past.

I appreciate that the show a vacuum gauge. Just over .10 on high, and half that on low. I am definitely no where near those numbers. Full exhaust fan power and high feed rate has me up over .5, while I haven't had a chance to play with low feed rate, with the exhaust fan basically off, .06 is the lowest I could get with the air inlet all the way open. Although on low, the exhaust temp will be lower, so the chimney draft should be lower as well, so it might be possible.

They also say that too much airflow will send some of your heat out your vent, which is the problem I think I've been having.

This stove has a scraper built in for cleaning the heat exchange tubes. Does anyone else have tips or suggestions for manually cleaning them, in case the scraper isn't doing a good enough job?

 

[Brokk]

Your flame looks lazy . Watch this video I know it is not
your stove but it is the best I have seen

Pellet Stove Flame (Pellet Stove Proper Flame)

Looking at the flame of a pellet stove (pellet stove flame) can be an early indication as to whether or not your pellet appliance is operating properly.

friendlyfires.ca

Here is a short video showing the flames when they are going well (meaning a good pellet supply has provided enough fuel for taller flames). I put a meat thermometer inside the heat tubes (yes, it's touching the metal), but I'm not getting vaguely close to the 500F you are reporting. Even with the circulation fan on medium, I'm hard pressed to get the temp up to 180F. More often it's in the 150s F. Exhaust temp at this time is just over 300F. Draft is around .15WC

BTW, I pulled the unit apart to clean the exhaust fan and circulation fan over the last couple days. When putting it back together I noticed a gap in the construction allowing air into the firebox. About a 1/4" gap where the feed shoot slides in to the firebox. So extra air was getting in. I closed that off now and the initial vacuum during startup is higher (.9WC), so it is making a difference.

 

[johneh]

ot getting vaguely close to the 500F you are reporting.

In order to reach that temp the stove is on high for at least 3 hours and only
when the outside temp hits -30 or colder in the middle of winter
To day it is 2 with a 30 km wind and the output of the stove (air) is 167
The Pipe is 124 and the stove is set at halfway on the dial a fire. Which is just
past the any lower pellet feed and I shut down on you point

 

[Brokk]

In order to reach that temp the stove is on high for at least 3 hours and only
when the outside temp hits -30 or colder in the middle of winter
To day it is 2 with a 30 km wind and the output of the stove (air) is 167
The Pipe is 124 and the stove is set at halfway on the dial a fire. Which is just
past the any lower pellet feed and I shut down on you point

Outside, your temp is colder and windier than here, but on low, your pellet stove is putting out double the heat of mine. Your exhaust temp is probably higher as well. I'm not entirely sure how the pipe temp relates to the temp inside a double wall. I would ask how many pellets you go through on low, but that's hard to gauge unless you burn a full bag on low and figure out how many pounds per hour. I could probably pull out my pellets, weigh them, put them back in, burn for 2 hours on high, then pull them out and weigh them again. I'm guessing I'm going through 3-4 pounds per hour on high.

How do you think my flames look in the video?

 

[johneh]

Fall and spring when temps. are above 0 it takes 30 to 36 hours to burn 0ne bag
normally. during the coldest part of the winter last 2 weeks of Jan. first 2 weeks of Feb
I will typically burn 1 1/2 bags a day on the very rare occasion 2 bags in 24 hours
In the 20 years, I have been burning pellets it has been the same every year with
little variance.
Your flame looks good
How clean is your heat exchanger? the part in the firebox
Ash is a fantastic insulator

 

[SidecarFlip]

Fall and spring when temps. are above 0 it takes 30 to 36 hours to burn 0ne bag
normally. during the coldest part of the winter last 2 weeks of Jan. first 2 weeks of Feb
I will typically burn 1 1/2 bags a day on the very rare occasion 2 bags in 24 hours
In the 20 years, I have been burning pellets it has been the same every year with
little variance.
Your flame looks good
How clean is your heat exchanger? the part in the firebox
Ash is a fantastic insulator

Interestingly, my pellet usage is almost exactly the same as you. Once I start adding corn and increasing the heat output it climbs but not much. Corn burns hitter than pellets depending of course on how dry it is.

I've never measured the heat output on my stove. I just do the 'seat of my pants' measurement.

 

[Brokk]

Fall and spring when temps. are above 0 it takes 30 to 36 hours to burn 0ne bag
normally. during the coldest part of the winter last 2 weeks of Jan. first 2 weeks of Feb
I will typically burn 1 1/2 bags a day on the very rare occasion 2 bags in 24 hours
In the 20 years, I have been burning pellets it has been the same every year with
little variance.
Your flame looks good
How clean is your heat exchanger? the part in the firebox
Ash is a fantastic insulator

The exposed tubes usually look good with light dusting of white ash on them. I discovered some build up behind the scraper. While I was cleaning it out, decided to take the firebox plate off to clean behind it and in the process made a shocking discovery (to me).

My understanding is that the heat should rise from the fire in the grate, up and pass over the heating tubes and down behind that wall. There was quite a bit of ash built up behind the wall, but that should not direct impact the heating tubes. However...

Next to the heating tubes, on both sides, there is a 2"x3" opening that leads to the same area behind the wall. So I have 12 square inches of opening for the hot exhaust to go, that mostly avoids the heating exchange tubes completely. That doesn't sound right to me. Did someone mess up at the factory? Or is this some safety design in case the path around the tubes gets blocked?

 

[Brokk]

Fall and spring when temps. are above 0 it takes 30 to 36 hours to burn 0ne bag
normally. during the coldest part of the winter last 2 weeks of Jan. first 2 weeks of Feb
I will typically burn 1 1/2 bags a day on the very rare occasion 2 bags in 24 hours
In the 20 years, I have been burning pellets it has been the same every year with
little variance.
Your flame looks good
How clean is your heat exchanger? the part in the firebox
Ash is a fantastic insulator

I looked up some old posts in 2008 when I was first reporting issues with low heat. At that time I was using a 40# bag every 8 hours or so.

 

[johneh]

I have no idea if that is a design flaw or
what but the ash build up back there is why
people keep saying is your stove clean . It is behind
things and hidden passages that get plugged and
compromise the output and operation of the stove

 

[SidecarFlip]

Why I use my super sucker shop vac with it's big power motor. I use a reducer on the end of the hose and a crevice tool that fits into all the nooks and crannies and sucks everything out. When it's sucking good (clean drywall bag), the crevice tool sounds like a jet engine....

I can even get into the combustion blower plenum and suck that out as well.

I've always maintained that the biggest cause of inefficiency is ash buildup. a 'Deep Clean to me is getting it all out.

I kind of dislike that term anyway. Deep Clean can mean most anything in reality.