New Owner - Efficiency Question

[rleshane]

Hi There!

New pellet stove owner here. Harman Accentra freestanding. Installed a few weeks ago by the shop I bought it from. Why did I choose a harman accentra? I really wanted a pellet stove, and my wife did not. She thought the big black boxes were ugly. We compromised by agreeing to get one if she had veto power on "ugly" models. She really liked the look of the Accetra (complete with optional legs), and it seemed like a quality stove from the research I did (although a bit pricey), so we went for it. We had it painted, and I have to say it looks quite sharp in our living room.

Now that I have it, there is no looking back and I want to get the best bang for my buck in terms of efficiency. I knew it was undersized from the time I first looked at it (40,000 btu in a 2400 square colonial style home). BUT, it's an extremely well insullated 4 year old house, and I planned all along on supplementing it with my traditional natural gas heat already in the house as needed.

Ok, that's the background, now to my question. For the past week or so temps during the day have been in the 50's, and high 20's to low 30's on the colder nights. At it's lowest setting (1 pound per hour), that little thing throws out (imo) some decent heat. At 2 pounds per hour, I guess it throws more heat, but it doesn't seem to be double the heat, even though I'm using twice as many pellets. Perhaps I'm wrong, heat output seems hard to "measure". My question is this. Should I be getting double the heat from burning double the pellets? Or would it make sense that I'm going to get a set amount of heat buring at 1 pound per hour, and more heat from burning 2 pounds, but not necessarily double? Is there a rate at which I'll get the best "bang for my buck" when it comes to pellets? Natural gas isn't cheap, but neither are pellets. Could it be that my best "bang for my buck" is at 1 pound per hour?

Thanks for taking the time to read all of this and respond. I would also welcome any additional tips you think this new stove owner could use.

Ron

 

[Corie]

It really comes down to how the heat exchanger was designing, the flow rate it was optimized for, etc. Really there should be a "sweet" spot where pellet usage and efficiency cross at some maximum point. It is probably around the medium to medium-high range. However, unless the heat exchanger efficiency drops of significantly with higher flow rates, you should be getting nearly 2x the heat from burning 2x the pellets.

 

[pelletheat]

Old thread on Harman settings with details of operation, read stovemanken's post on Harman. I hope this helps.....

https://www.hearth.com/talk/threads/4082/

 

[rleshane]

Thanks for that fast reply Corie. What you said certainly seems to make sense. It also makes me question how much the circulation fan speed plays into the equation. You mentioned a "sweet" spot which is what I am after. Do you think the circulation fan speed impacts that sweet spot? Or would running the the circulation fan on it's highest setting always pull the maximum amount of heat from the exchanger?

 

[Corey]

Corie is probably one of the best people to answer this, so nothing more to add there.

I will only say that 'seat of the pants' measurement of temperature/ efficiency is extremely difficult at best. Even assuming all the other parameters were identical through different burns (outside temp, wind, humidity, indoor temp, etc) Say you burn on setting 1 and the house gets to 70F, then you go to setting 2 and burn 2x the pellets. How do you gauge the heat? Do you expect the indoor temp to double go to 140F ? Probably not. Do you expect the stove to be twice as hot, probably not a good assumption either. Likewise, the air coming off the stove won't be twice as hot either.

 

[rleshane]

Thanks so much for posting that link pellethead. Stovemanken's last posting in that thread blew me away. Not only because it had so much great info, but more importantly because it gave advice completely OPPOSITE of what I recevied from the guy that installed my stove! Ouch.

Stove temp vs. room temp. My installer said running on Stove Temp was by far the most efficient way to run, because it's a steady flow (that you can adjust) and doesn't go "up and down". Yet Stovemanken's post says Room Temp is the more efficient way to run. I be so confuse

I would MUCH rather run on room temp as stovemanken suggests (if it's truely most efficient), since I could "set it and forget it", not having to manual monitor outside and inside temps to make ajustements.

Thoughts?

 

[Corie]

One easy way to find that "sweet" spot is to monitor the exhaust gas temperature. At whatever setting you find the lowest EGT, you have a pretty good idea the heat exchanger is operating near its maximum efficiency. Of course, the temp on low will be higher than that on high but if you have microsoft excel, you can make a simple plot which will get you somewhere near the area of maximum efficiency.

You can change the blower speed, pellet feed and then monitor exhaust temp, fill in the chart and bingo, you've got it.

If that explanation doesn't help, I can whip something up here in a few minutes.

 

[rleshane]

How completely brilliant Corie! That makes perfect sense. Thanks so much for the idea!

Any advice on finding a low cost tool for measuring EGT? I'm guessing sticking my hand in the pipe with a traditional thermometer probably isn't the best approach.

 

[pelletheat]

Feedrate of at least 4, Room Temp w/distribution blower low-med setting, igniter on auto.

Once the temperature approaches your setpoint, the software will begin to adjust the feedrate accordingly during the 60 second cycles to maintain your room temperature setpoint. The distribution blower & combustion blower will modulate according to the heating demands. I prefer the distribution blower on low-med because of this feature, stove is in the same room as the TV, the blower will adjust to higher speeds automatically when burning at a higher output and drop back when the heating demand drops.

Sometimes when the weather hits a cold streak, I flip the igniter switch to manual so the stove will never shutoff, it will idle back to a maintenance burn of 7-10 seconds every minute if the room temperature is satisfied.

 

[rleshane]

wow, im getting all sorts of great advice today. I also was able to PM with Stovemanken who answered my questions about room temp vs stove temp modes.

Last question for pellethead, when you say you put your circulation fan on low-med, and that it adjusts itself as needed, does that mean it will adjust itself down and up to your setting, but not above your setting? Like if you put it on medium, would it adjust itself between low and medium as needed in room temp mode, but never go above medium?

 

[GVA]

wow, im getting all sorts of great advice today. I also was able to PM with Stovemanken who answered my questions about room temp vs stove temp modes.

Last question for pellethead, when you say you put your circulation fan on low-med, and that it adjusts itself as needed, does that mean it will adjust itself down and up to your setting, but not above your setting? Like if you put it on medium, would it adjust itself between low and medium as needed in room temp mode, but never go above medium?

1. If you put the speed on low it will run on low (unless ESP thinks stove is overheating then it will default to High)
2. If you put the speed on high it will always run on high (eventually blowing cooler air into the room (since it removes all the energy from the heat exchangers)
3. If you put the speed anywhere in between the L & H it will run on low when the room needs minimal heat and will ramp up to what ever sped it needs to satisfy the room temp settings. That is You will hear the blower adjust itself.

 

[rleshane]

1. If you put the speed on low it will run on low (unless ESP thinks stove is overheating then it will default to High)
2. If you put the speed on high it will always run on high (eventually blowing cooler air into the room (since it removes all the energy from the heat exchangers)
3. If you put the speed anywhere in between the L & H it will run on low when the room needs minimal heat and will ramp up to what ever sped it needs to satisfy the room temp settings. That is You will hear the blower adjust itself.

Ah Ha! Thank you so much! What a timely response. As I'm getting use to my new stove I tried room temp (instead of stove temp) 2 nights ago and was very disapointed and frustrated when the fan never automatically kicked itself down from the high setting I had it at. Your explination above is music to my ears, because at least now I understand how that part works. I swear I don't understand why they can't put basic information like that in the owners manual Along those lines, is there any publicly available documentation on Harmans that might have this type of information?

 

[FireJumper]

As far as I know RonL there isn't any information out there explaining this. There is alot of good information on the site below but I don't believe they reference any of the information questioned above.

(broken link removed)

 

[rleshane]

As far as I know RonL there isn't any information out there explaining this. There is alot of good information on the site below but I don't believe they reference any of the information questioned above.

(broken link removed)

Thanks for the link. I'll look through it. It's a shame really... nice stove, poor documentation. But, I guess I would rather that than great documentation and a crapy stove.

 

[FireJumper]

If you could have your cake and eat it too then what would be the point of a discussion board? :lol:

 

[GVA]

Ron page 7 of your manual....ESP control, under distribution blower adjustment covers part of this..... the hi temp saftey is not
FWIW all Harmans appear to use the same control board...
Homewarmth is just a link to the Harman site but I have e-mailed them several times to update for the now 2 year old XXV cleaning procedures...... DEALERS how 'bout some help on this..................

 

[rleshane]

Ron page 7 of your manual....ESP control, under distribution blower adjustment covers part of this..... the hi temp saftey is not
FWIW all Harmans appear to use the same control board...
Homewarmth is just a link to the Harman site but I have e-mailed them several times to update for the now 2 year old XXV cleaning procedures...... DEALERS how 'bout some help on this..................

Although the manual says the dial adjusts the variable speed blower, and that the range will vary based on stove temp, it makes no mention (unless I am blind) of how the ESP works with this. The ESP will adjust the fan rate on it's own (kicking it up and down) if it is set to anything BETWEEN high and low. If set to H or L, it will overide this feature and force the circulation fan to always be on high or low. None of that is mentioned in the manual, which I find rediculous.

 

[GVA]

Ron page 7 of your manual....ESP control, under distribution blower adjustment covers part of this..... the hi temp saftey is not
FWIW all Harmans appear to use the same control board...
Homewarmth is just a link to the Harman site but I have e-mailed them several times to update for the now 2 year old XXV cleaning procedures...... DEALERS how 'bout some help on this..................

Although the manual says the dial adjusts the variable speed blower, and that the range will vary based on stove temp, it makes no mention (unless I am blind) of how the ESP works with this. The ESP will adjust the fan rate on it's own (kicking it up and down) if it is set to anything BETWEEN high and low. If set to H or L, it will overide this feature and force the circulation fan to always be on high or low. None of that is mentioned in the manual, which I find rediculous.

The Room temp probe controls blower speed. ESP if too hot will tell board to speed up blower and help pull excess heat away. That is is room temp mode...
Stove temp mode relies on exhaust temp(ESP) and will turn blower up, down, on, and off to keep the exhaust temp the same..
And HarryBack said it best on the manuals....... "You don't expect the owners manual for your car to tell you how the engine works, do you?"
Thats why these guys are here....