Anyone with a p68 getting anything close to 68,000 btu's out?

[Mt Bob]

Like the old pinto going 100mph-down a mine shaft!

 

[IHATEPROPANE]

Its could be just some Harman fuzzy math. It can probably input 68k btus when the stove is cold until the esp is as hot as allowed for the first hour.....then never gets there again.

 

[J1809]

Ok, thank you everyone. I guess I didn't read carefully enough when I bought it and wanted to believe that unlike every other product out there the marketing guys weren't actually writing the ads.

So, if I burn pelletized charcoal with a petroleum binder, hook the intake to a pure oxygen source, and power vent it directly out the back at a -50 degree ambient temperature I can get 68000 btus of consumption. What a chump I am.

 

[Harman Lover 007]

Ok, thank you everyone. I guess I didn't read carefully enough when I bought it and wanted to believe that unlike every other product out there the marketing guys weren't actually writing the ads.

So, if I burn pelletized charcoal with a petroleum binder, hook the intake to a pure oxygen source, and power vent it directly out the back at a -50 degree ambient temperature I can get 68000 btus of consumption. What a chump I am.

C'mon don't be so hard on yourself......

 

[chken]

Hi,

Here's my problem, and I would love to hear from anyone who is getting close to 68000 btus out of their p68: I installed a p68 this Fall, and in the highest settings--stove temp 6, feed rate 7, distribution blower all the way high-- I burn a little more than 3 bags/day. This is true of the $5/bag pellets that the stove dealer sells and the $4/bag pellets from home depot.


If the pellets are about 8500 btus/lb and I burn 3 bags/day or 120 lbs/day, I burn 5lbs/hr so I'm inputting about 42500 btu's. This is at the max settings, so clearly I'm not getting anything like 68,000 btu's out.


I've spoken with the dealer and with Harman, and although draft test pinned when it was installed, both the dealer and Harman have said that my exhaust set up has some restrictions in it so the ESP won’t allow the stove to run hotter.


I kind of believed it until this week when temperatures got to minus 10 and I used an online engineering calculator to figure out that the pressure in my flue was twice what it is when the outside temperature is 30 degrees. I'm still only able to burn the same three bags/day even though it's much colder outside and the natural draft is twice as strong.


So I am suspicious of the 68000 btu rating or of the 8lbs/hr burn rating and so I really wonder if anyone is able to burn more than 3 bags/day with their p68? I figure that if you could run the stove at 8lb/s hr, which the manual says is possible and the pellets were 9500btu's/lb and the stove really is 89% efficient then you might get to that 68000, so it's pretty pie in the sky, but my 5lbs/hr regardless of ambient temperature, is so far from that number that I really wonder.


Please let me know and thank you in advance.

Jared from western NY

Interesting problem and something I've thought about since I bought my stove in November.

Your calculations look correct to me, you should be able to burn 5 bags a day, if your stove really were maxing out at 68k btus, which it clearly is not.

I started a thread a little while back to see how many bags people were burning on the coldest days of the year:
https://www.hearth.com/talk/threads/poll-how-many-bags-do-you-burn-on-the-coldest-days.121035/

If you look, only 10 people out of 84 people burned 3 or more bags a day on the coldest days of the year, so there really aren't that many people here needing to burn more than 40k btus, ~3 bags, to begin with. Would be nice to know who those 10 people were, and if they were P68 owners. Then again, I burned 3 bags on one day last week, and I've got a much smaller stove that is only rated for 47k btus. However, that does mean, I was able to get closer to my stove's rated input, than you were able to.

Burning 3 bags put me at about 88% of my stove's rated capacity. I probably could have burned more if I had not setback my thermostat at night. If you're burning a little over 3 bags, out of a 5 bag capacity, then you're at a little over 60% of your rated input capacity. I doubt that 40% margin is marketing. Something's not quite right.

Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?

 

[chken]

I'm sure in a lab we can get that stove to really hit 68k, but you'd need a seriously cold space to strip off enough heat from the unit to tell the ESP to tell the CB to "eat more pellets"...in the end, its still a max temp at the ESP that tells the stove what to do. Making more BTUs without either, more surface area, or more convection air, the internal temp doesn't drop enough to make the stove work any harder. You also have a max auger speed of 6RPM (i thinks) and pellets are pretty oddly shaped so there might be a "theoretical" ability that is just prohibative to acheive...like MPG on cars...its nice pretty numbers, just not always that realistic...and of course YMMV.

Surely, a P68 doesn't need to be in a lab to achieve more than 40k btus, though, cause that's what the OP is getting. I mean if he were at 90% of its rated input capacity, then the variability of pellet sizes, become a factor, but he's only at 60%

 

[chken]

It's possible that my exhaust set up does not allow enough airflow over the ESP to cool it to get to those higher BTU numbers, But again, I'm really curious to hear from anyone who gets there before I punch into my masonry chimney to change the T to 4" all the way..

Did Harman or the dealer tell you that you needed to change your exhaust vent to 4"? I'd think their word would be far more important than anyone in this forum. Does any of the P68 brochures or manuals, state in the fine print, that you need a 4" vent to achieve its rated capacity? You'd think the dealer would tell people they don't need a P68 and can just get a P61 or P52 if they aren't going to use a vent sized for that amount of output.

 

[BrotherBart]

Did Harman or the dealer tell you that you needed to change your exhaust vent to 4"?

Page 8 of the manual.

 

[SmokeyTheBear]

Now I'm not just talking about a P68 but any pellet stove has to have enough (not to little) so called negative pressure in the firebox in order for it to operate. Too little and the vacuum switch shuts off the auger and the fire dies down, now with the nice cold temps it is possible that the volume of air in the OPs flue is such that the pressure difference isn't there once the burn rate gets up to a certain point, this is a self limit on the pellet feed and is the direct result of an improper venting situation. Now I'm talking about Harman products and any other product that can operate to a set sensor in its exhaust. This situation can also result in a back-pressure in the venting that traps hot air in the area here the esp is and if you are in stove mode this is the only temperature.
sensor that counts. I believe that the Harman's adjust pellet feed to match the difference in the temperature the stove is set for and the temperature seen by the stoves sensors. This results in a ramp down as the set point is approached.

The OP should read the sticky dealing with Harman operation at the top of this forum.

You can test the pressure issue by a Jerry rig but it really isn't a safe thing to do, the best thing to do is talk to your dealer about getting a DDM attached to the device and seeing what the stoves computer is seeing from its sensors and to verify that the dip switches on the controller are set correctly.

That stove cranked open is a beast and fed the correct pellets it can produce some serious heat.

 

[IHATEPROPANE]

Thank you. Harman's glossy brochure calls it an output...hmmm from:

http://hearthnhome.com/downloads/brochures/HAR-1110U.pdf
....P68 PEllEt StovE
the award-winning p68 is a home heating
powerhouse. it produces up to 68,000 BtUs—...

I agree the spec sheet you link to show sit as an input number though. So if we assume it's an input number ,and we find a pellet that's even 10k btu's/lb, then we'd still need to put roughly 7lbs/hr in so about 168 lbs/day or something a little over 4 bags/day. I'm wondering if anyone is doing that.

Granted my LP furnace is ducted, but it's not huge and it's rated 100k btu's out. So I would think that there are people with open floor plans or heating big insulated space etc, that would max the stove out like I'd like to. It's possible that my exhaust set up does not allow enough airflow over the ESP to cool it to get to those higher BTU numbers, But again, I'm really curious to hear from anyone who gets there before I punch into my masonry chimney to change the T to 4" all the way..

If you google Harman P68 4 bags/day ot 5bag/day there are no hits at all.

I really appreciate all the responses.
Thanks, Jared

What is your venting set up now?

 

[rona]

No, I want more heat out. It's not an academic exercise.

Hi,

Here's my problem, and I would love to hear from anyone who is getting close to 68000 btus out of their p68: I installed a p68 this Fall, and in the highest settings--stove temp 6, feed rate 7, distribution blower all the way high-- I burn a little more than 3 bags/day. This is true of the $5/bag pellets that the stove dealer sells and the $4/bag pellets from home depot.


If the pellets are about 8500 btus/lb and I burn 3 bags/day or 120 lbs/day, I burn 5lbs/hr so I'm inputting about 42500 btu's. This is at the max settings, so clearly I'm not getting anything like 68,000 btu's out.


I've spoken with the dealer and with Harman, and although draft test pinned when it was installed, both the dealer and Harman have said that my exhaust set up has some restrictions in it so the ESP won’t allow the stove to run hotter.


I kind of believed it until this week when temperatures got to minus 10 and I used an online engineering calculator to figure out that the pressure in my flue was twice what it is when the outside temperature is 30 degrees. I'm still only able to burn the same three bags/day even though it's much colder outside and the natural draft is twice as strong.


So I am suspicious of the 68000 btu rating or of the 8lbs/hr burn rating and so I really wonder if anyone is able to burn more than 3 bags/day with their p68? I figure that if you could run the stove at 8lb/s hr, which the manual says is possible and the pellets were 9500btu's/lb and the stove really is 89% efficient then you might get to that 68000, so it's pretty pie in the sky, but my 5lbs/hr regardless of ambient temperature, is so far from that number that I really wonder.


Please let me know and thank you in advance.

Jared from western NY

Hi,

Here's my problem, and I would love to hear from anyone who is getting close to 68000 btus out of their p68: I installed a p68 this Fall, and in the highest settings--stove temp 6, feed rate 7, distribution blower all the way high-- I burn a little more than 3 bags/day. This is true of the $5/bag pellets that the stove dealer sells and the $4/bag pellets from home depot.


If the pellets are about 8500 btus/lb and I burn 3 bags/day or 120 lbs/day, I burn 5lbs/hr so I'm inputting about 42500 btu's. This is at the max settings, so clearly I'm not getting anything like 68,000 btu's out.


I've spoken with the dealer and with Harman, and although draft test pinned when it was installed, both the dealer and Harman have said that my exhaust set up has some restrictions in it so the ESP won’t allow the stove to run hotter.


I kind of believed it until this week when temperatures got to minus 10 and I used an online engineering calculator to figure out that the pressure in my flue was twice what it is when the outside temperature is 30 degrees. I'm still only able to burn the same three bags/day even though it's much colder outside and the natural draft is twice as strong.


So I am suspicious of the 68000 btu rating or of the 8lbs/hr burn rating and so I really wonder if anyone is able to burn more than 3 bags/day with their p68? I figure that if you could run the stove at 8lb/s hr, which the manual says is possible and the pellets were 9500btu's/lb and the stove really is 89% efficient then you might get to that 68000, so it's pretty pie in the sky, but my 5lbs/hr regardless of ambient temperature, is so far from that number that I really wonder.


Please let me know and thank you in advance.

Jared from western NY

Your dealer questioned your exhaust system as a possible cause. Could you describe your exh system? How long is it? How many elbows etc.

 

[kinsmanstoves]

Are you running this stove in an un-insulated warehouse? I would look more towards insulation than attempting to burn 8 pounds of pellets per hour.

Eric

 

[J1809]

Interesting problem and something I've thought about since I bought my stove in November.

Your calculations look correct to me, you should be able to burn 5 bags a day, if your stove really were maxing out at 68k btus, which it clearly is not.

I started a thread a little while back to see how many bags people were burning on the coldest days of the year:
https://www.hearth.com/talk/threads/poll-how-many-bags-do-you-burn-on-the-coldest-days.121035/

If you look, only 10 people out of 84 people burned 3 or more bags a day on the coldest days of the year, so there really aren't that many people here needing to burn more than 40k btus, ~3 bags, to begin with. Would be nice to know who those 10 people were, and if they were P68 owners. Then again, I burned 3 bags on one day last week, and I've got a much smaller stove that is only rated for 47k btus. However, that does mean, I was able to get closer to my stove's rated input, than you were able to.

Burning 3 bags put me at about 88% of my stove's rated capacity. I probably could have burned more if I had not setback my thermostat at night. If you're burning a little over 3 bags, out of a 5 bag capacity, then you're at a little over 60% of your rated input capacity. I doubt that 40% margin is marketing. Something's not quite right.

Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?

That's a great survey. It would be interesting to me to know what stoves they used.


<<Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?


This is the way my p68 vents.:There's a 3" diameter adapter on the stove's exhaust flange that goes into 18" long of double walled 3" pipe, this pipe connects to a 3" double walled 'T', which is mounted horizontally (so I can get at the cleanout). From the 'T', a 3" double wall pipe runs about 24" total into the masonry chimney into a vertically positioned 'T' which takes it from 3" pipe to 4" pipe. The 'T' connects to a 4" insulated flex liner that rises 28' straight up inside the chimney.

I don’t know if the picture will post:

The setup was ok'd by the dealer when the installer came to draft test my setup, during which the draft meter pinned. So it all seemed good.


I have a old leaky house, and I wanted to really get the heat out of the stove and so back before it go very cold, I found I couldn’t get anywhere near the 5 bags/day. When I spoke with the dealer's installer, and with a Harman rep, and they suggested that I eliminate the first 'T' and just go straight out from the stove all with 4" diameter into a new vertically position 4" T in the chimney. This would eliminate one 'T' and also make it 4" all the way. They suspected that there isn't enough airflow over the ESP to burn more than what I burn now. It made sense to me at the time and intended to do it in the spring.


Then we had all the really cold weather and using the draft flow calculator on this site:

http://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html


I guestimated that the natural draft improved by about 10% over the warmer days. It's a small difference, but still something and I thought I'd ask here if anyone was able to get more than 3 bags worth before I go and buy the new liner pieces etc etc.


From the responses so far, I just feel like an idiot for spending all that money on a p68, to get ~40k BTU's out, when maybe there are cheaper stoves that could do it.


I may try the 4" changes anyway, b/c I'm already stuck with the p68.


Thank you

 

[J1809]

Are you running this stove in an un-insulated warehouse? I would look more towards insulation than attempting to burn 8 pounds of pellets per hour.

Eric

I'm 'restoring' my old house and need to insulate in a way that doesn't interfere with the aesthetics that I want. Insulation and tightening are happening, but more heat now is what's possible.

 

[J1809]

Now I'm not just talking about a P68 but any pellet stove has to have enough (not to little) so called negative pressure in the firebox in order for it to operate. Too little and the vacuum switch shuts off the auger and the fire dies down, now with the nice cold temps it is possible that the volume of air in the OPs flue is such that the pressure difference isn't there once the burn rate gets up to a certain point, this is a self limit on the pellet feed and is the direct result of an improper venting situation. Now I'm talking about Harman products and any other product that can operate to a set sensor in its exhaust. This situation can also result in a back-pressure in the venting that traps hot air in the area here the esp is and if you are in stove mode this is the only temperature.
sensor that counts. I believe that the Harman's adjust pellet feed to match the difference in the temperature the stove is set for and the temperature seen by the stoves sensors. This results in a ramp down as the set point is approached.

The OP should read the sticky dealing with Harman operation at the top of this forum.

You can test the pressure issue by a Jerry rig but it really isn't a safe thing to do, the best thing to do is talk to your dealer about getting a DDM attached to the device and seeing what the stoves computer is seeing from its sensors and to verify that the dip switches on the controller are set correctly.

That stove cranked open is a beast and fed the correct pellets it can produce some serious heat.

""talk to your dealer about getting a DDM attached to the device and seeing what the stoves computer is seeing from its sensors and to verify that the dip switches on the controller are set correctly.""

Good idea, thank you. I'll call and get in their book for this. FWIW, the last time I spoke with the dealer I explained about the 5lbs/hr max thing and they assured me that if I had the settings all the way up, I was getting 68k btu's out. They really brushed me off as soon as the draft test was done imo.

 

[J1809]

I'm 'restoring' my old house and need to insulate in a way that doesn't interfere with the aesthetics that I want. Insulation and tightening are happening, but more heat now is what's possible.

Fwiw, in 2010 we had ~5600 heating degree days and burned about 1200 gallons of LP to keep the house pretty ehh. A small zone near 70 the rest in the low 60's/high50's. I've tightened and insulated some since then, but it's still pretty leaky etc and not an open floor plan so we rely on p68 + doorway fans etc..

 

[Mt Bob]

That's a great survey. It would be interesting to me to know what stoves they used.


<<Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?


This is the way my p68 vents.:There's a 3" diameter adapter on the stove's exhaust flange that goes into 18" long of double walled 3" pipe, this pipe connects to a 3" double walled 'T', which is mounted horizontally (so I can get at the cleanout). From the 'T', a 3" double wall pipe runs about 24" total into the masonry chimney into a vertically positioned 'T' which takes it from 3" pipe to 4" pipe. The 'T' connects to a 4" insulated flex liner that rises 28' straight up inside the chimney.

I don’t know if the picture will post:

The setup was ok'd by the dealer when the installer came to draft test my setup, during which the draft meter pinned. So it all seemed good.


I have a old leaky house, and I wanted to really get the heat out of the stove and so back before it go very cold, I found I couldn’t get anywhere near the 5 bags/day. When I spoke with the dealer's installer, and with a Harman rep, and they suggested that I eliminate the first 'T' and just go straight out from the stove all with 4" diameter into a new vertically position 4" T in the chimney. This would eliminate one 'T' and also make it 4" all the way. They suspected that there isn't enough airflow over the ESP to burn more than what I burn now. It made sense to me at the time and intended to do it in the spring.


Then we had all the really cold weather and using the draft flow calculator on this site:

http://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html


I guestimated that the natural draft improved by about 10% over the warmer days. It's a small difference, but still something and I thought I'd ask here if anyone was able to get more than 3 bags worth before I go and buy the new liner pieces etc etc.


From the responses so far, I just feel like an idiot for spending all that money on a p68, to get ~40k BTU's out, when maybe there are cheaper stoves that could do it.


I may try the 4" changes anyway, b/c I'm already stuck with the p68.


Thank you

View attachment 123578

Looks like you answered your own questions.Page 9 of your manual-"4" pipe if over 15 foot run",also chimney that high,looks like you will never get max from that unit.Suggest study manual,make installer change the 3" and plan on better vent system for max power.

 

[harttj]

That's a great survey. It would be interesting to me to know what stoves they used.


<<Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?


This is the way my p68 vents.:There's a 3" diameter adapter on the stove's exhaust flange that goes into 18" long of double walled 3" pipe, this pipe connects to a 3" double walled 'T', which is mounted horizontally (so I can get at the cleanout). From the 'T', a 3" double wall pipe runs about 24" total into the masonry chimney into a vertically positioned 'T' which takes it from 3" pipe to 4" pipe. The 'T' connects to a 4" insulated flex liner that rises 28' straight up inside the chimney.

I don’t know if the picture will post:

The setup was ok'd by the dealer when the installer came to draft test my setup, during which the draft meter pinned. So it all seemed good.


I have a old leaky house, and I wanted to really get the heat out of the stove and so back before it go very cold, I found I couldn’t get anywhere near the 5 bags/day. When I spoke with the dealer's installer, and with a Harman rep, and they suggested that I eliminate the first 'T' and just go straight out from the stove all with 4" diameter into a new vertically position 4" T in the chimney. This would eliminate one 'T' and also make it 4" all the way. They suspected that there isn't enough airflow over the ESP to burn more than what I burn now. It made sense to me at the time and intended to do it in the spring.


Then we had all the really cold weather and using the draft flow calculator on this site:

http://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html


I guestimated that the natural draft improved by about 10% over the warmer days. It's a small difference, but still something and I thought I'd ask here if anyone was able to get more than 3 bags worth before I go and buy the new liner pieces etc etc.


From the responses so far, I just feel like an idiot for spending all that money on a p68, to get ~40k BTU's out, when maybe there are cheaper stoves that could do it.


I may try the 4" changes anyway, b/c I'm already stuck with the p68.


Thank you

View attachment 123578

I'm one that burns more than 3 on the coldest day and don't have a P68, just need to find the other nine now. I'm burning corn now and during the polar vortex and 25 mph winds was hitting 81,000 btu input. This was a new record for me and hope I never hit it again. This was 100% of my heating. I did bypass the DHW to prioritize heat to the house.

Tim

 

[Mt Bob]

I don't envy your burning!Hope weather breaks your way soon.Seems like third or forth year now that your area and new england are having worse weather than us.

 

[TheMightyMoe]

Just for info...

My home was rated at required 58k BTU @ -60 per energy audit, my boiler is rated at 60k, and keeps up just fine.

I heat my whole house with the P68, and it isn't even maxed out on feed rate, nor temperature settings.

In the coldest weather it does use 3+ bags a day, which equates to around 100k BTU. We also keep the house toasty, 80 downstairs 70+ upstairs, where as with the boiler typically around 60F.

Room temp with a thermostat set around 75-80.

A warm woman is a happy woman I suppose.

 

[chken]

That's a great survey. It would be interesting to me to know what stoves they used.


<<Can you tell us what those "restrictions" your dealer and Harman was talking about? Do you need a bigger vent diameter?


This is the way my p68 vents.:There's a 3" diameter adapter on the stove's exhaust flange that goes into 18" long of double walled 3" pipe, this pipe connects to a 3" double walled 'T', which is mounted horizontally (so I can get at the cleanout). From the 'T', a 3" double wall pipe runs about 24" total into the masonry chimney into a vertically positioned 'T' which takes it from 3" pipe to 4" pipe. The 'T' connects to a 4" insulated flex liner that rises 28' straight up inside the chimney.

I don’t know if the picture will post:

The setup was ok'd by the dealer when the installer came to draft test my setup, during which the draft meter pinned. So it all seemed good.


I have a old leaky house, and I wanted to really get the heat out of the stove and so back before it go very cold, I found I couldn’t get anywhere near the 5 bags/day. When I spoke with the dealer's installer, and with a Harman rep, and they suggested that I eliminate the first 'T' and just go straight out from the stove all with 4" diameter into a new vertically position 4" T in the chimney. This would eliminate one 'T' and also make it 4" all the way. They suspected that there isn't enough airflow over the ESP to burn more than what I burn now. It made sense to me at the time and intended to do it in the spring.


Then we had all the really cold weather and using the draft flow calculator on this site:

http://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html


I guestimated that the natural draft improved by about 10% over the warmer days. It's a small difference, but still something and I thought I'd ask here if anyone was able to get more than 3 bags worth before I go and buy the new liner pieces etc etc.


From the responses so far, I just feel like an idiot for spending all that money on a p68, to get ~40k BTU's out, when maybe there are cheaper stoves that could do it.


I may try the 4" changes anyway, b/c I'm already stuck with the p68.


Thank you

View attachment 123578

Well, I think all fingers are pointing at the 3" venting as the "restriction".

 

[J1809]

Well, I think all fingers are pointing at the 3" venting as the "restriction".

 

[J1809]

Thank you all for all the help. In the Spring, I'll redo the venting and post back next winter. The dealer really did me a disservice and I appreciate all the help here. I was realy starting to lose it.

 

[chken]

Thank you all for all the help. In the Spring, I'll redo the venting and post back next winter. The dealer really did me a disservice and I appreciate all the help here. I was realy starting to lose it.

FWIW, I think the dealer/installer should have said something about how the 3" vent would restrict the stove's capability. I mean, it should have been obvious to an experienced installer that the OP's house was big, old, and drafty. I mean, why do people get P68s to begin with, if not to heat a large space?

 

[Jacques909]

I think I could easily burn 3 bags/day...in fact, I struggle to burn less than 2-2.5 bags/day. My P68 is a basement dweller, and it heats a total of almost 3000 sqft. I run it in Room Temp, usually set for 72-75°F. I've never had to turn it above 75°F, and it throws a ton of heat. I can't imagine running it on MAX, I think it would melt my face off. I haven't really tried Stove temp, I always assumed running in Room temp would burn less pellets.

I LOVE my P68...I installed it in September, and over Christmas we lost power for 3 days during the ice storm. My P68 and Champion generator kept us warm and toasty while some of my neighbors were forced to leave their homes for Christmas.

What kind of generator? Inverter? How many watts? Thanks