Curious about output temp differences

MarkSJohnson · Dec 29, 2013

So, I'm new to pellet stoves and have only had one for a couple of months. As many here recommend, I bought approximately 12 different brands of pellets and tried them all. Unfortunately, I didn't own an infrared thermometer while going through the first four brands or so, but I got temp readings for the latter brands.

The very first brand I tried was Fireside Ultras. Again, I didn't have the thermometer yet, but they seemed to burn an awful lot hotter than the next few brands I bought. When I finished with all the rest of the other brands, the Fireside Ultras seemed like a logical choice to buy for the season (3 tons). Especially since others here were reporting them as burning hot and they coincidentally happened to be the cheapest pellets I found I found at a little over $200/ton.

Now that I'm burning them exclusively, and have the ability to measure those temps at the room blower vents, they don't seem particularly hot.... just kind of mid-range. I really wish I had my thermometer from the beginning rather than just anecdotal information, but I'm feeling pretty confident that I'm not getting the same heat that I did initially.

I'm curious if it might be as simple as these three tons being from a different batch, or is it because my stove is not as clean as new?

I've read of pellet brands varying in quality from season to season, but do they also have quality variances from batch to batch? Can a person assume that if they bought Brand X today and liked the results, that the quality would be the same 2 months later? Or do you guys buy a few bags from a specific batch before committing to tons for the season?

And, if it's the stove, is it normal to maybe have a 60 degree difference in the temp readings between a "Clean as new" stove and one that's been used for a couple of months? I THINK I'm cleaning it pretty thoroughly...and yesterday in particular did a really thorough job around the heat exchange tubes. The only thing that has not been well-cleaned is the vent pipe.

What say you, Pellet Aficionados?

IHATEPROPANE · Dec 29, 2013

Pellet batches differ.
There is a big difference between a clean stove and a dirty one.
Cold outside temps will lower the output temps
Infared measure heat if the metal...not air
I am assuming the same feed rate is set and that you let the stove come up to temperature before getting temps.

IHATEPROPANE · Dec 29, 2013

You should look up leaf blower trick....youbthink your stove is clean until.you do this.

Phil Do's fire. · Dec 29, 2013

MarkSJohnson said:
So, I'm new to pellet stoves and have only had one for a couple of months. As many here recommend, I bought approximately 12 different brands of pellets and tried them all. Unfortunately, I didn't own an infrared thermometer while going through the first four brands or so, but I got temp readings for the latter brands.

The very first brand I tried was Fireside Ultras. Again, I didn't have the thermometer yet, but they seemed to burn an awful lot hotter than the next few brands I bought. When I finished with all the rest of the other brands, the Fireside Ultras seemed like a logical choice to buy for the season (3 tons). Especially since others here were reporting them as burning hot and they coincidentally happened to be the cheapest pellets I found I found at a little over $200/ton.

Now that I'm burning them exclusively, and have the ability to measure those temps at the room blower vents, they don't seem particularly hot.... just kind of mid-range. I really wish I had my thermometer from the beginning rather than just anecdotal information, but I'm feeling pretty confident that I'm not getting the same heat that I did initially.

I'm curious if it might be as simple as these three tons being from a different batch, or is it because my stove is not as clean as new?

I've read of pellet brands varying in quality from season to season, but do they also have quality variances from batch to batch? Can a person assume that if they bought Brand X today and liked the results, that the quality would be the same 2 months later? Or do you guys buy a few bags from a specific batch before committing to tons for the season?

And, if it's the stove, is it normal to maybe have a 60 degree difference in the temp readings between a "Clean as new" stove and one that's been used for a couple of months? I THINK I'm cleaning it pretty thoroughly...and yesterday in particular did a really thorough job around the heat exchange tubes. The only thing that has not been well-cleaned is the vent pipe.

What say you, Pellet Aficionados?

A good pellet company such as Hamers Hot Ones and Okies are about the same year after year. They have refine the process and quality is consistent year after year. Other companies like stove chow or tractor supply brand have there pellets produced at different locations and different processes leading to inconsistent product. Hope this helps and yes a 60 degree difference is not uncommon with a dirty stove or inferior pellet.

boomhour · Dec 29, 2013

Have to agree with Phil, Mark. My own stove will run on low setting at about 310 f with a bag of LG's and Trebio's will run up into the 360-375 f range. This is with normal cleaning of the stove every two weeks. I also use a ray gun that was tested for accuracy, although it is not the air temperature, it is just plain hot.This pic was with the stove on setting 4 for about 20 min or so.

MarkSJohnson · Dec 29, 2013

Thanks to all of you for your responses.

To measure the temps, I ensure that the stove has been on setting "3" for at least half an hour, and have taken 5-6 measurements over a period of 5 minutes or so to help average the fluctuations. I keep the thermometer at the same distance and measure the same spot on one of the "fins" in the middle of the room blower output. So I feel pretty confident that the measurements are useful at least as far as different pellets relative to each other if not the actual dead-on accurate temp at any given reading.

I'm planning on cleaning the vent pipe today for the first time. That's likely to change the output temp of the room blower?

IHATEPROPANE · Dec 29, 2013

MarkSJohnson said:
Thanks to all of you for your responses.

To measure the temps, I ensure that the stove has been on setting "3" for at least half an hour, and have taken 5-6 measurements over a period of 5 minutes or so to help average the fluctuations. I keep the thermometer at the same distance and measure the same spot on one of the "fins" in the middle of the room blower output. So I feel pretty confident that the measurements are useful at least as far as different pellets relative to each other if not the actual dead-on accurate temp at any given reading.

I'm planning on cleaning the vent pipe today for the first time. That's likely to change the output temp of the room blower?

Yes, as long as you are consistent with your temp taking the numbers are useful.
to get a good feel for which pellets are actually hotter than others you need to measure the actual pellet usage. There can be a significant difference in lbs/hr amongst brands.

pell it · Dec 29, 2013

MarkSJohnson said:
So, I'm new to pellet stoves and have only had one for a couple of months. As many here recommend, I bought approximately 12 different brands of pellets and tried them all. Unfortunately, I didn't own an infrared thermometer while going through the first four brands or so, but I got temp readings for the latter brands.

The very first brand I tried was Fireside Ultras. Again, I didn't have the thermometer yet, but they seemed to burn an awful lot hotter than the next few brands I bought. When I finished with all the rest of the other brands, the Fireside Ultras seemed like a logical choice to buy for the season (3 tons). Especially since others here were reporting them as burning hot and they coincidentally happened to be the cheapest pellets I found I found at a little over $200/ton.

Now that I'm burning them exclusively, and have the ability to measure those temps at the room blower vents, they don't seem particularly hot.... just kind of mid-range. I really wish I had my thermometer from the beginning rather than just anecdotal information, but I'm feeling pretty confident that I'm not getting the same heat that I did initially.

I'm curious if it might be as simple as these three tons being from a different batch, or is it because my stove is not as clean as new?

I've read of pellet brands varying in quality from season to season, but do they also have quality variances from batch to batch? Can a person assume that if they bought Brand X today and liked the results, that the quality would be the same 2 months later? Or do you guys buy a few bags from a specific batch before committing to tons for the season?

And, if it's the stove, is it normal to maybe have a 60 degree difference in the temp readings between a "Clean as new" stove and one that's been used for a couple of months? I THINK I'm cleaning it pretty thoroughly...and yesterday in particular did a really thorough job around the heat exchange tubes. The only thing that has not been well-cleaned is the vent pipe.

What say you, Pellet Aficionados?

Last year I really liked the Fireside Ultras. This year I got stuck with a not so great (being nice) ton. I'm getting clinkers and so-so heat from them. They are struggling with the 30 degree temps at night. I am burning thru them in this little warm spell and will blend the last few bags I have with my Greene Teams and Vermonts to get rid of them. Batch Variance is always a possibility with manufacturers who buy fiber on the open market.

ChandlerR · Dec 29, 2013

Mark, I installed a type J thermocouple temperature controller on mine. The thermocouple is in one of the heat exchanger tubes. You can see it on the top left. I see a 10 to 15 degree increase after my weekly cleaning and a 20 degree increase after my monthly cleaning. Because it's always on, I can monitor how the stove is running and take action if needed. Because I'm burning Vermonts exclusively, my temps stay steady. I see 160 to 170 on low and 340 to 350 on high. (Picture taken on low)
I got the controller from work. It was thrown out because the contacts inside burned out but all I needed was the temp display.

chken · Dec 29, 2013

MarkSJohnson said:
I'm planning on cleaning the vent pipe today for the first time. That's likely to change the output temp of the room blower?

I was going to recommend cleaning the vent pipe, as you stated you had had a stove for a couple months. You're probably over a ton burned already, and should do a cleaning to get a sense of how often you should do it.

Madcodger · Dec 30, 2013

There is a definite difference between brands, and as noted, between batches / lots for some brands. Hamer's have been consistently great and the hottest I've ever burned of about 5 different brands (least ash, as well). PrestoLog looking surprisingly good as well, but no idea about batch variation. Measuring output temps with an infrared on the little Whit in my office is my way of comparing brands and has become my conference call "hobby" (pace with headset on, hold infrared, point at stove. So I probably get about 20-40 measurements / week).

Cleanliness of stove also matters, but I can say that I don't "overdo" this. I vacuum out the firebox and ash drawer weekly, and give the stoves a thorough monthly cleaning (exhaust ports, back of heat exchangers, etc). But vent pipes and pulling motors? End of season only. I'm sure there is some loss of efficiency by sometime in February, but it's frankly not noticeable to me in terms of pellet consumption or comfort. Then again, I'm generally burning very high quality, low ash pellets and it's my first year for the little Whit in the office (4th for Quad MVAE).

skibumm100 · Dec 30, 2013

As others have said, it varies batch to batch and season to season. Some suppliers probably have less batch to batch variation. I would think Cubex/Northern should be pretty consistant since they make their own sawdust from hardwood flooring. Probably LaCrete (sawmill) too. I had a "cold" ton of Vermonts last year but I think that's pretty rare. They were very low ash but FSU's stomped them, with respect to heat, as almost all the other brands I tested did. I checked them against "hot" Vermont's from last year and Vermont's from this year and they were definitely "colder" by 40 deg measured at the outlet grill with a type K thermocouple. I have a similar setup to ChandlerR. Your IR gun temperature readings are a good relative measurement but don't use them to compare to other peoples readings. FYI, most cheap IR guns are fixed emisivity so they are generally not very accurate unless the object you're measuring has the same emisivity as the gun is set up for. Errors of 50 deg F from surface type/color to surface type/color are not uncommon. They will work for relative measurement, though. As another FYI, the output air temperature measured at the grille of my stove only reaches a maximum of about 260 deg F with the hottest pellets running on high and about 230 deg F with crappier pellets. Big difference with waht other people are reporting. I'm not sure how much difference flue cleanliness has to do with heat output into the room. My thouhgt is that that is more a function of the heat exchanger cleanliness. Once the flue gas leaves the heat exchanger passes, the rest is waste heat that you gain no benefit from.

MarkSJohnson · Dec 30, 2013

I'm now getting much higher readings with my Fireside Ultras. Not from cleaning my vent, but from re-adjusting the fresh air intake.

When the stove was new, it seems as though I had the air damper open 1/4 of the way (approximately). Over the last couple of months, I've opened it a bit more and a bit more, looking for that happy medium between a lazy flame and what the manual describes as a "blow-torch-like" flame. It seems as though it now is doing better with it only being about 1/4 open again.

What I need to do is to experiment with feed rate trim, damper settings, etc., now that I've settled on one pellet. That wasn't realistic when I was trying a multiude of pellets and burning something different every other day.

Thank you all again for your help though! I still have lots to learn!

Phil Do's fire. · Dec 31, 2013

MarkSJohnson said:
I'm now getting much higher readings with my Fireside Ultras. Not from cleaning my vent, but from re-adjusting the fresh air intake.

When the stove was new, it seems as though I had the air damper open 1/4 of the way (approximately). Over the last couple of months, I've opened it a bit more and a bit more, looking for that happy medium between a lazy flame and what the manual describes as a "blow-torch-like" flame. It seems as though it now is doing better with it only being about 1/4 open again.

What I need to do is to experiment with feed rate trim, damper settings, etc., now that I've settled on one pellet. That wasn't realistic when I was trying a multiude of pellets and burning something different every other day.

Thank you all again for your help though! I still have lots to learn!

As long as the pellets are not bouncing out of the burn pot area, don't be conservative with the air. My Old Whitfield ran with the air more than 3/4 open and my Palazzetti adjusts automatically and burns like a blow torch. You will get much more heat with a very active flame!

skibumm100 · Dec 31, 2013

I think that's true to a point. You can check the temperature of the convection air outlet to get the max output temp. If you have a temperature sensor in the exhaust flue you can adjust it for the maximum convection outlet temp and the minimum flue gas temp. That would be the most efficient operation for a particular pellet on a particular manual stove setting. It's all about heat transfer and complete combustion. Too much combustion air and your blowing your BTU's up the chimney. Every stove and installation is a little different. I would tune for max output temperature on a manual setting. Just my $0.02.

Madcodger · Dec 31, 2013

Excellent points. Essentially, max temp of convection air for least pellets used, so long as flame quality is good. Always a "dial it in" challenge, but then again we're addicted to it! Still cheaper than golf, and more productive than TV. So not a bad hobby...

Harvey Schneider · Dec 31, 2013

skibumm100 said:
My thouhgt is that that is more a function of the heat exchanger cleanliness. Once the flue gas leaves the heat exchanger passes, the rest is waste heat that you gain no benefit from.

Vent restriction due to ash buildup can be as subtle as a thin but textured layer. It doesn't have to be plugged with ash to mess with the fuel to air ratio. So, while I agree that all heat exchange has already happened before the flue gasses reach the vent, I believe that the quality of the fire can be negatively impacted by a dirty vent system.

skibumm100 said:
I would tune for max output temperature on a manual setting

Tuning for max temperature with the convection blower at the highest tolerable setting (the most noise your ears will allow) will get the max heat out of the stove. Raising the convection temperature by reducing the convection speed will give a satisfyingly hot air flow, but at the expense of poor efficiency. Heat exchangers are most efficient when the difference between hot side and cold side is the greatest..
Tuning for maximum hot side temperature will get the most heat out of the stove for a fixed convection speed, but it may not be at the optimum efficiency. Like a car, stoves produce the most power at full throttle but don't necessarily operate as efficiently there..

skibumm100 · Dec 31, 2013

Harvey Schneider said:
Vent restriction due to ash buildup can be as subtle as a thin but textured layer. It doesn't have to be plugged with ash to mess with the fuel to air ratio. So, while I agree that all heat exchange has already happened before the flue gasses reach the vent, I believe that the quality of the fire can be negatively impacted by a dirty vent system.

Agreed. Under this condition you would have to open the inlet damper to compensate for the reduced air flow to get the same combustion air flow as a clean flue. You would have to reduce the pressure drop across the damper to make up for the increased drop in the dirty flue gas path.

Tuning for max temperature with the convection blower at the highest tolerable setting (the most noise your ears will allow) will get the max heat out of the stove. Raising the convection temperature by reducing the convection speed will give a satisfyingly hot air flow, but at the expense of poor efficiency. Heat exchangers are most efficient when the difference between hot side and cold side is the greatest..
Tuning for maximum hot side temperature will get the most heat out of the stove for a fixed convection speed, but it may not be at the optimum efficiency. Like a car, stoves produce the most power at full throttle but don't necessarily operate as efficiently there..

I should've mentioned that it would have to be at a fixed convection fan speed. Thanks. On my stove I don't have control of the convection fan speed independently from the fuel feed setting. For my stove, it's one less variable I can play with. If your stove has separate speed controls for the convection fan that complicates things. I think a lot of stoves do have that ability but my York does not. It's a very simple stove. Even the combustion trim only affects the lower heat settings. The only adjustment that I can tinker with is the inlet air damper. On a heat exchanger, it's all about delta T and fouling.

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