Temperature Variations

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becasunshine

Minister of Fire
Dec 10, 2009
708
Coastal Virginia
M'kay.

What would cause a 20-30'F temperature variation, given consistency in everything else?

Burning the same pellets, at the same settings, in a stove that is cleaned/vacuumed consistently every day. We use a deep fryer thermometer inserted in the far left heat exchanger. We can get 255'F out of that tube on one day, and then two days later we get 230'F out of the same tube- with all things the same. Today, we are struggling to reach 230'F.

????

The only difference may be how long the stove has been running when we take a temperature reading. The stove's been running about 1.5 hours since we last cleaned it and we are reading about 220'F to 225'F.

I just shut the damper down to 2. It looks like our pellets are burning down to almost nothing before the auger delivers more pellets. The stove's output temp started inching up almost immediately.

It's not particularly windy outside. It is cold, cloudy and humid.

This is when I (once again) begin to wonder if the OAK and outside air temps affect the stove's heat output.
 
beca,

A few of us have removed the OAK and seen no temp changes. But every stove and install acts differently. Maybe try to disconnect it and see if you get an increase in temps.

Keep us posted.
jay
 
Yanno, I rather like my OAK. I don't want to pull combustion air in through the cracks and crevices of this 1950s house. I think it's more of an academic exercise: why do I have such a large variation in output temps? and can I do anything to get the highest temps, consistently?

Does anybody else get these variations? Or am I doing something wrong? What causes the temp variations?
 
I really only see that large of a change when I change pellet brands. Once my stove is up to full temp its pretty steady. It does take about 2 hours for it to come up to full temp though. I guess it depends on the stove and maybe pellet length variations. Or maybe a low hopper level.

How long was the stove running when you took the really high temp reading? Maybe your stove takes a long time to get to full temp.
 
Devil in the details:

As I recall, we took the temperature not long after the start up, when we had the big fire that results from burning the initial pile of pellets in the pot. So, depending on how many pellets we pile up in the pot at start up, and how big that initial flame is, I guess that determines our initial temp.

Today we cut the feed back right after the burn pot caught fire, so not that many pellets piled up in the pot, and our initial flame wasn't as big or as enduring. And it appears that as a result, our running temp at outset wasn't that dramatic.

So we let the stove run for a couple of hours and we hit about 225'F.

I shut the damper a bit and it looked like the output temp was creeping up a bit.

I checked the stove temp about an hour later: 210'F. So that didn't work out so well.

So I opened the damper back up to 3. About 30-45 minutes later, the temp is reading about 220'F.

Again, I'm using a deep fryer/candy thermometer- not the most sophisticated tool available.

What is a typical output temp in a typical stove that is rated to produce up to about 40k BTUs? I dunno. Somebody here probably does.

Really, does it matter if the stove is putting out 225'F vs. 255'F? Practically? Probably not. But I am haunted by the idea of sending precious BTUs out of the exhaust pipe unnecessarily.

I don't have unrealistic expectations of the stove. It is what it is: a stove. It's not a furnace, it's not a central HVAC system, it produces X amount of BTUs and those BTUs will stretch so far, The End.

I do want to learn to use the stove at its most efficient settings, in the most efficient way. I want to put every BTU we've purchased to good use.

This exercise is a bit tedious but I suppose that this is how it's done: tweak, measure heat output. Tweak, measure heat output.

I'm getting to know my stove, and I'm taking y'all along for the ride.

Thank you for all of the useful, practical feedback, btw. We do appreciate it!
 
becasunshine said:
Devil in the details:



A.) What is a typical output temp in a typical stove that is rated to produce up to about 40k BTUs? I dunno. Somebody here probably does.

B.) Really, does it matter if the stove is putting out 225'F vs. 255'F? Practically? Probably not. But I am haunted by the idea of sending precious BTUs out of the exhaust pipe unnecessarily.

I don't have unrealistic expectations of the stove. It is what it is: a stove. It's not a furnace, it's not a central HVAC system, it produces X amount of BTUs and those BTUs will stretch so far, The End.

I do want to learn to use the stove at its most efficient settings, in the most efficient way. I want to put every BTU we've purchased to good use.

This exercise is a bit tedious but I suppose that this is how it's done: tweak, measure heat output. Tweak, measure heat output.

I'm getting to know my stove, and I'm taking y'all along for the ride.

A= I don't really know. Just try to get it as high as possible with a decent burn.

B= IMO yes. If you didn't change anything it should be close. I would keep an eye on it. Are you sure you didn't change anything?

Seems like you got a good handle on it. Just remember to do small adjustments and 1 adjustment at a time.Give the stove some time to adjust to the change. I recommend a log to keep track of it all. Chance to much and it could go south on you. This is the tinkering part and takes time to learn what the stove likes. I only see major temps changes when I change pellet brands. Usually the pellet batch temps stay very close to the same.

Watching someone learn there stove is OK by me. I just hope I have offered some insite that is useful for you. Just remember to have fun with it. If it gets frustrating take a break. With good notes you can generally get to a decent starting spot.
 
M'kay. Here's my final answer:

225'F, give or take a degree or two, literally.

I think 255'F was an abherration- a high temp from a big fire at start up. I'm gonna throw that temp reading out.

I've taken several readings now, including readings taken after the stove had run for several hours.

All readings put us at 225'F.

So, at feed 4, damper 3 our output temp is 225'F, and we are burning about one bag of pellets in 24 hours.

Is 225'F a good heat output?

The owner's manual recommends a feed setting of 4 as the most efficient setting- so we'll go with that.
 
becasunshine said:
M'kay. Here's my final answer:

225'F, give or take a degree or two, literally.

I think 255'F was an abherration- a high temp from a big fire at start up. I'm gonna throw that temp reading out.

I've taken several readings now, including readings taken after the stove had run for several hours.

All readings put us at 225'F.

So, at feed 4, damper 3 our output temp is 225'F, and we are burning about one bag of pellets in 24 hours.

Is 225'F a good heat output?

The owner's manual recommends a feed setting of 4 as the most efficient setting- so we'll go with that.

Doesn't sound bad. If its keeping the house warm on the coldest days and you are not using the furnace to assist the pellet stove. I would say thats what you need. You now also have a base temp for testing other pellet brands. If you tried a different brand and there temps are lower. You might want to call them shoulder pellets. If the new brand is hotter save them for the extreme cold.

The biggest reason I temp check my stove was to see where the stove keeps up in the extreme cold. Then I use that temp as a base line for my pellet search. Hotter pellets for cold- lower temp for the should season. But if you can afford all hotter pellets then just make sure they meet the minimum temp that keeps you warm without over working the stove with the max setting. I prefer to see my stove at the 3 or 4 setting. Running it at the max to me over work's the stove and stresses it.

I think you get the hang of it. Enjoy!
 
Lose your thermometer... really. I'd worry about how warm my living space is... I could care less if the stove is putting out -20F or +1000F... as long as I'm warm don't care.

When Jtakeman was testing pellets it was neat to see the different temps... but trying to micro-manage a wood-fired appliance will give you headaches... and nothing else...IMHO.
 
I would think the stove would give a fairly even temp rise given all conditions are consistent, pellet brand, control settings, ect. I've never checked mine, and may do so today, but 160* rise seems very reasonable. Maybe the fluctuations in discharge air temperature are a result of the return air temperature to the stove. Usually in heating and cooling equipment the delta T is what we are most concerned with.
 
krooser said:
Lose your thermometer... really. I'd worry about how warm my living space is... I could care less if the stove is putting out -20F or +1000F... as long as I'm warm don't care.

When Jtakeman was testing pellets it was neat to see the different temps... but trying to micro-manage a wood-fired appliance will give you headaches... and nothing else...IMHO.

Hmmm, I'll buy that. No need to over do it I guess. Check temps to compare pellets and maybe stove damper changes. May also use as a aid in monitoring cleaning. If the temps drop maybe its time to clean the stove or heat exchangers.

I get bored in the winter so I tinker. Takes little time to check the temp. I'll compare it to checking the water temp on the old hotrod. I don't do much if its consistent.
 
Ok krooser,

Here's an example for you. I checked my stove temp this morning. Was at 250ºF. Normally running The O malley's I was getting 225ºF to 235ºF(can't see the flame my glass is dirty) so I idle the stove to low. Wait a bit and wipe the glass. Crank her back up to the medium setting. Yep flame is a bit lazy. Grab my magnahelic gauge and take a reading. Hmmm .105 rather low, I usually get .125. Shut down the stove and let it cool. Get the winter cold gear on and hit the vent. Sure enough my 2 ft horizontal was almost plugged(right at the outside of the thimble). Get the brush and vac to clean her up. Its all good now. Mag reading went over .14(adjust back to .125) and my stove temp is back to 225ºF. Looks like I need to do a complete cleaning when I get a warmer day. You know the leafblower method you tought us! I think its time. I have never really run my stove on the Hi/Lo setting and I guess it will cause the ash to collect in the vent more. Its only been 28 bags since my last full cleaning. I usually get to 50 no problems but I don't push it past 40 most of the time.

Just another tool to use. Granted not every day.

Sorry if I bugged you :p
jay
 
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