Combustion fan question for the experts.

[EarthStove]

Well, my Earthstove MP 35/50 has decided to start acting up again.

Unburned pellets, burn pot stuck full of clumping ash etc. Happens with every pellet I have tried this year. Seems to be the worst on medium feed setting and only after running for about 10 to 12 hours continuous. The first 10 to 12 hours everything seems perfect. Great flame, ash dumping off the sides etc.

Stove is clean as a whistle.

Here is where I am going with this. I decided that it's gotta be a combustion fan issue. Perhaps the fan is just to old (going on 17 years old now). When the stove is feeding pellets on medium setting the combustion fan runs at 100%, then when it's not feeding it drops down to about 60% (I think) then kicks back up again when the fed starts. I think maybe that after 10 to 12 hours of running the motor is just getting to hot and losing efficiency or something like that. If we cool the stove down and clean the burn pot it will go good for another 10 to 12 hours. If all I do is clean the burn pot the ash builds up again much faster. and we are back to clumping in just a few hours.

So I decided to buy a larger combustion fan. I got a Fasco B75 rated at 75 CFM. The current fan is rated at 45 CFM.

So I cut the old fan out and installed the new one. Both fans are just hanging off the back right now not attached to the stove. So I ran a feed cycle to see if this new fan blew more air than the old one. Seems to me that the new fan at the very most is about the same amount of air. What am I missing here? Shouldn't the new fan be blowing out more air since it's 75 cfm vs. 45 cfm? It seems like it might even be less air when the fed system is not feeding (60% power to the fan).

I really like this stove but it may be the end of the line unless I can get some help understanding this fan thing.

Thanks!

 

[smwilliamson]

Use the parts the stove was designed to be used with first of all. The thing that you are missing here is that the stove engineered to work a certain way in concert with the other systems. Your problem could be the phase controller in the control board...that dictates the voltage to the motor you have. I would have tested that before I bought a new motor.

 

[Harvey Schneider]

Questions:

1. Is the speed variation you describe the way the stove has always worked or is this a new behavior?
2. Do you hear a different fan speed when the stove is hot (vs when it is cold)?
3. Is the stove really clean? (including vent pathways)
   
4. Have you checked for air leaks into the fire box? (you may need to check with a candle when the stove is hot)

What you are describing sounds like incomplete combustion so I have to assume that it is caused by insufficient combustion air.
Motors usually run better when warm than when cold, but you could have an exception. The reason I say that is bearings get gummy with age and the heat helps to open clearances resulting in freer motion. If a motor is thermally protected, it will usually shut down as opposed to running slower. Is the motor intermittently shutting down and causing the incomplete combustion?

An oversize combustion blower is not the solution. The design worked at one time, redesigning to fix something that should work isn't a good approach. With the larger blower you are going to be blowing too much air through the fire box and out the vent. This will cause a loss in efficiency, wasting pellets.

These are just the things that come to mind right now. I am sure others will have something to add.

 

[EarthStove]

The fan speed is designed to slow down when not feeding pellets. It varies depending on what the feed setting is set at. I used to have the service manual that had the voltage outputs for each setting. I think low was like 60 volts, medium was 80 volts and high was 110 volts or something like that.

Fan speed sounds the same to me anyway regardless of whether it's hot or cold but it's hard to tell. No huge differences.

There are no other places to clean the stove that I am aware of. Every thing is clean including the 4" vent pipe from the back of the stove to the top. This stove uses a "push" type combustion setup where the combustion fan is before the fire pot.

The reason I went with a bigger fan this time is the fact that the damper setting on the old fan has never really had an effect. Meaning it was once set up to block about 1/3 on the combustion fan opening. If I opened it more it did not change the combustion in the fire pot. Now if I closed it down it would. I figured that with more air I could then have more adjustment on the air flow by way of the damper. A few weeks ago we were able to run several days without any clogs. The same brand of pellet even after a cleaning produced a different result with clumping of ash etc. There just does not seem to be any rhyme of reason to it so I figure it has to be variations in the quality of the pellet even with-in the same brand.w So, if I figured if I can get more air to it I might have some more flexibility here.

Also, the original replacement fan is not available for this stove anymore. I do believe that places that sell the replacement fan are using a larger CFM fan as well but it might be rated at 65cfm and not 75. Although I have seen a Fasco B30 motor that might be a closer match But again, I figured having more air would give me greater flexibility.

The stove also has three combustion fan settings.... OFF, Low and High. I have always kept it on high. Any other setting (obviously) would lead to incomplete combustion.

We are kinda at wits end with the stove though and are thinking about a new Harman or something else but really don't have the money right now to purchase a new one. So a band-aid on this one would be awesome.

 

[EarthStove]

I measured the voltage coming off the fan here re the results:

Draft fan switch set to high

When feeding pellets: 119volts
Not feeding pellets on medium feed setting: 74 volts
Not feeding pellets on low feed setting: 74 volts.

Draft fan switch set to low

When feeding pellets: 119volts
Not feeding pellets on medium feed setting: 63 volts
Not feeding pellets on low feed setting: 63 volts.


Our controller board is the older style natural file board not the natural fire controller board 2000.

From the manual for the controller board 2000 it says that on medium it should read 90 volts. Medium low should read 65 volts. Not sure the settings are the same on each board or not for the designated low, medium and high.

 

[EarthStove]

OK,
So I found my copy of the service manual.

It says in the troubleshooting section I should be seeing between 70 and 75 volts when the stove is not feeding.

In the beginning of the manual it says I should be seeing 75% of the max voltage when the stove is not feeding (which is 90 volts) or 50% of the max voltage when the draft fan is set to low (60 volts)

Which is it?
If the troubleshooting section is correct then I am seeing the proper voltages at least while the stove is cold. If the other section is correct then the stove is not pushing enough air when the medium setting is selected.

What do you guys think?

 

[Harvey Schneider]

Does that stove have any hidden ash traps? Check your manual carefully.

 

[Harvey Schneider]

Just came across this on another thread

I worked on an old Earth Stove (Traditions). It is a positive pressure stove, had a bad burn. Finally figured that the area just under the top of the stove was clogged with ash. They are using the top vent. I removed two bolts, and the entire top of the stove came off, making it very easy to clean the heat exchanger and all the passages. Stove burns great now. No mention of this in the manual, either, and the dealer never heard of doing this.

 

[EarthStove]

Yeah I saw that too. I believe he was referring to another stove model though.

The Mp 35/50 is quite simple in it's design. I had that stove torn apart and the only place that ash can hide is above the baffle that is just beneath the exchange tubes and above the tubes. Then there is an area in the back, top area of the stove where the top vent would connect (we use the rear vent). then the small outlet that leaves that area then makes a 45 degree turn downward and then out the back of the stove. Unless there is some weird completely hidden area that I cannot see I think I have been cleaning the entire stove.

Also wouldn't have problems immediately upon firing the stove up? When we first light it, the flames look great and the pellets burn completely.

 

[EarthStove]

Here is a screen shot of the stove from the manual:

 

[MSmith66]

Did you remove the top of the stove when you clean it? I went to a home with the same stove and they said they cleaned the stove. When I removed the top of the stove, there was no move room for anything in there. It was packed with ash. After cleaning every baffle and top channels the stove ran a lot better.

 

[Harvey Schneider]

Here is a screen shot of the stove from the manual:


View attachment 124031

It is hard to see at first but that diagram indicates a baffle just below the top exit. According to the diagram the back exit uses the same path. I would check it out before I did anything else.

 

[EarthStove]

Did you remove the top of the stove when you clean it? I went to a home with the same stove and they said they cleaned the stove. When I removed the top of the stove, there was no move room for anything in there. It was packed with ash. After cleaning every baffle and top channels the stove ran a lot better.

When you say remove the top of the stove, what do you mean?

I have removed the top plate (top chimney outlet) which is a small roughly 4"x4" piece of steel. I cleaned the entire area above the baffles from there. I checked this area again last night and it appears that it's clean and clear.

Are you saying to remove the entire top of the stove? I don't see how this is possible. It looks like it's welded steel on all 4 corners.

 

[heat seeker]

On the Traditions model I referred to, there is a bolt on each side, top center, that screws up into the top. It catches on a flange on the side of the stove to hold the top on. The top is cast iron; it took two of us to safely remove it, as it's heavy. If yours is sheet metal, it's probably a different design. Once the top was off, there was a sheet metal baffle that lifted out, and cleaning was quite straightforward. The passage that goes down to the rear exit was packed, but since it wasn't used, and the vacuum had very limited capacity, we left that alone. The diagram posted above seems accurate, although the stove manual the owner had didn't have that.

 

[EarthStove]

Yeah, our stove is sheet metal. There is also a sheet metal shield that surrounds the stove that is cool to the touch.

 

[EarthStove]

So, tonight I took a bore scope and looked inside the stove.

The top baffle was pretty clear but I did scrub it with a metal bottle brush and now that entire area is completely clean. It only had some residual ash on it from the last burn.

I checked all passages and everything is clear. Nothing was blocked that would cause the air flow to be hindered.

I put the old combustion blower back on and hooked the stove back up to the exhaust pipe and sealed everything up. I am going to run it tomorrow and then check some voltage on the combustion blower once things start to clog up again.

I don't know what else to do at this point. The stove is clean, the voltages *appear* to be right (unless the voltage should be 90 instead of 65 but there is no way to tell at this point with conflicting values in the service manual)

 

[EarthStove]

After all that the stove is still causing ash to clump. Will have to wait longer but I just scraped after about 10 hours of burning on medium and it was already starting to get a little clumpy. It happens at the edges were the "coolest" part of the burn occurs.

I am beginning to believe this must be an inherent problem with all pellet stoves in general with the quality of the pellets available on the market today regardless of brand or so called "quality" Just reading this forum the past two days it seems that people with other brand "clean" stoves are running into the same problems as us. Even when we went to the dealer to see a Harmon P68 in operation. It had two clumps on the left and right side of the burn pot.

Incidentally, the American wood fiber softwood pellets are putting out some really good heat. I measured over 370F right at the blower outlet with my digital IR thermometer.

The stove in the fire pot was reading 540F, 14" out the back on the pipe it was reading 120f so pretty efficient cooling going on as well.

 

[Madcodger]

I have an old Whitfield Quest from early-mid 90s and a 2010 Quad MVAE. I've burned Hamer's, Presto, Stove Chow, Cheat River, Green Supreme, Nature's Own, and both hardwood and softwood Cleanfire over four seasons. I have never had the clumping you describe, or a clinker. And I can't imagine scraping a firepot after 10 hours as my MVAE goes a week in peak season without being touched except for adding pellets, and the old Whit gets only a vacuuming of the firebox around the pot to remove ash every day or two. Both get a decent cleaning once / month to clear out the smaller channels but motors come off and brushes through vents only in the off season, after about two tons each (first year for the Whit for me, but no reason to suspect otherwise after more than half of season gone).

It's not the pellets.. Something's wrong with stove or install...

 

[chken]

After all that the stove is still causing ash to clump. Will have to wait longer but I just scraped after about 10 hours of burning on medium and it was already starting to get a little clumpy. It happens at the edges were the "coolest" part of the burn occurs.

I am beginning to believe this must be an inherent problem with all pellet stoves in general with the quality of the pellets available on the market today regardless of brand or so called "quality" Just reading this forum the past two days it seems that people with other brand "clean" stoves are running into the same problems as us. Even when we went to the dealer to see a Harmon P68 in operation. It had two clumps on the left and right side of the burn pot.

Incidentally, the American wood fiber softwood pellets are putting out some really good heat. I measured over 370F right at the blower outlet with my digital IR thermometer.

The stove in the fire pot was reading 540F, 14" out the back on the pipe it was reading 120f so pretty efficient cooling going on as well.

Maybe it's not the combustion fan? You said the stove is clean, but you didn't say if the vent was clean.

If the vent is clean, then perhaps you need to play with your air settings to get more air into the burn pot.

If that isn't possible, then look at your burn pot holes. Are specific holes clogging? Have you considered enlarging them?

My stove is obviously different from yours, but it took me a while to dial in my stove. I had similar symptoms, but not to the same degree as yours. Flame would get lazy about 12 to 16hrs in. Some holes would block. I increased air, and enlarged the burn pot holes slightly. Now, my burn looks just as good 24hrs in, as it does in the first hour. All pellet brands burn nicely now.

 

[EarthStove]

Thanks for the input. Unfortunately, air input is limited in settings. Off, low and high for the combustion fan and pellet feed is low, medium or high. This is why I wanted to get a bigger fan into the stove with more CFM. Then I would dial it back with the damper attached to the air intake on the combustion fan.

A quick update though on the problem. We decided to switch pellet brands and try Hamers Hot Ones again. I have been (was) burning them on medium since last night and we have not had a single clinker/clumping ash. So, must be the pellets right? Thing I can't figure out is I was burning Hardwood heat (supposed to be the same as Hamers) and had the clumping going on. Maybe it's the way the pellets are handled? Tractor supply leaves these things outside, bags are frequently damp on the outside etc.

Comparing the Hamers hot ones to the Hardwood heat, the color, size etc all look the same.

I have 3 more bags of the AWF softwood to burn when the Hamers are gone - we'll see if the clumping returns.

 

[EarthStove]

Almost 48 hours running now with the Hamers Hot Ones and not a single clump/clinker. I took he ash pot out today to look and the ash is a light fluffy dust. So, is it just the pellet quality? Is there anything that I can do to help get a better burn without the clinkers with other brands?

 

[Stevekng]

Almost 48 hours running now with the Hamers Hot Ones and not a single clump/clinker. I took he ash pot out today to look and the ash is a light fluffy dust. So, is it just the pellet quality? Is there anything that I can do to help get a better burn without the clinkers with other brands?

I noticed that your signature says you had new logs in 2011. Are you using the cosmetic logs that make the burn chamber area look like a wood fired fireplace? If so, then try running with out them. I made the mistake of using them on my VF 100 when I first bought it and my stove filled up with ash because the logs trapped the ash above the burn pot rather than letting it drop onto the grate below. Everything was the way it should be after that.
It could be that your voltage issue could be a supply issue. Have you checked your house current. If you have an older house like I do (1850) then wiring was an afterthought when electricity became available. I have three generations of wiring in my house. cloth shielded, 1st gen plastic shielded, and new stuff less than 10 years old. If you have older wiring, you could be loosing current before in gets to your stove.

 

[EarthStove]

Thanks Steve,
We have run with and without the logs. The logs are situated in such a way that they don't affect the flame or ash in any meaningful way. They are well above the fire pot. I ran it for a while without the logs and it made no difference with different brands of pellets.

Our house is "new". We built it ourselves about 15 years ago. Voltage checks out OK.

 

[EarthStove]

Well we just picked up a ton of Hamers to finish out the winter. We'll see how they work out. So far the 6 bags we put through it have worked out perfectly.