Harman control board - how you waste pellets on the "stove temp" mode

[smwilliamson]

Harman stoves have two modes of operation, "stove temp" and "room temp". By turning the mode knob either up or down you select your mode. This knob is a multifunctional knob as it not only changes between the two operating modes but it also adjusts the fan speed for the distribution blower.

In the room temp mode the stove is monitoring the room temperature via the room thermistor probe. As the room cools or becomes warmer the stove is able to monitor progress and modulate the stove's heat output to ramp up or down the feed to meet demand respectively. Regardless of the distribution fan setting, the thermistor probe will control the stove's output, even ultimately turning the stove on or off as required.

If you choose to run the dove on the "stove temp" mode, the only sensor controlling the stove is the ESP (exhaust sensing probe). Stove temp mode uses the numbers 1 through 7 on the inside of the temperature dial. In this mode the stove is seeking to achieve and maintain an exhaust temp between 350 degrees (#1) and 500 degrees (#7). Here's the issue....

The mode selection knob still allows the user to control the distribution blower but the stove does not know what setting the blower is at. The amount of heat that is extracted from the heat exchanger varies according to how much room air is being transferred; the higher the fan setting, the more heat that is removed from the exhaust, thus will affect the ESP reading.

If you run in stove temp, simply adjusting the room distribution fan up will cause the stove to consume more pellets!

Here was my test on my P61 using 40lbs of LaCrete pellets in two separate runs:

First run was on Stove temp mode setting #5 moderate fan (middle), 40 lbs in about 12 hrs

Second run was on stove temp mode setting #3 with fan on high (all the way up), 40 lbs in about 9 hrs

Even though I adjusted down my heat setting, as the manual would suggest, I got less burn time out of 40lbs by using the high fan setting.

For both runs my feed rate was set to 4

I had always wondered about this scenario and finally got a moment of clarity over the weekend when I filled the hopper Friday about 7pm and at 8 the next morning it was empty and sputtering out. I filled it again but this time turned the fan up and kicked the heat setting down...by 6 that night the stove was completely out again.

I've had many customers over the years complain that for whatever reason, the stove just chews through pellets at times and at other times seems fine. It was always my assumption that this was the culprit....so no longer a myth.

Any of you out there care to back this theory I'd love it...especially someone with hardwood pellets, though I don't know if that would really make a difference.

 

[Big papa]

Good stuff thanks for the info would have taken me a while to stumble across that.

 

[Don2222]

Harman stoves have two modes of operation, "stove temp" and "room temp". By turning the mode knob either up or down you select your mode. This knob is a multifunctional knob as it not only changes between the two operating modes but it also adjusts the fan speed for the distribution blower.

In the room temp mode the stove is monitoring the room temperature via the room thermistor probe. As the room cools or becomes warmer the stove is able to monitor progress and modulate the stove's heat output to ramp up or down the feed to meet demand respectively. Regardless of the distribution fan setting, the thermistor probe will control the stove's output, even ultimately turning the stove on or off as required.

If you choose to run the dove on the "stove temp" mode, the only sensor controlling the stove is the ESP (exhaust sensing probe). Stove temp mode uses the numbers 1 through 7 on the inside of the temperature dial. In this mode the stove is seeking to achieve and maintain an exhaust temp between 350 degrees (#1) and 500 degrees (#7). Here's the issue....

The mode selection knob still allows the user to control the distribution blower but the stove does not know what setting the blower is at. The amount of heat that is extracted from the heat exchanger varies according to how much room air is being transferred; the higher the fan setting, the more heat that is removed from the exhaust, thus will affect the ESP reading.

If you run in stove temp, simply adjusting the room distribution fan up will cause the stove to consume more pellets!

Here was my test on my P61:

Stove temp mode setting #5 moderate fan (middle), 40 lbs in 12 hrs; stove temp mode setting #3 high fan 9 hrs.

Even though I adjusted down my heat setting I got less time out of 40lbs by using a high fan setting.

Those of you with Harmans..use a lower fan speed if you want your pellets to last longer and just let the stove become a radiant heater.

How old is your P61 circuit board Scott? Is it a Manual CB? Is it an older Auto Lite board where the mode knob does not have a click in off position? Which ESP probe are you using the old black Analog or the new Red digital probe? The new boards are so different in their heat algorythms, that may not be the case.
I have the latest CB and in room temp mode the board will shut down the distribution blower completely to maintain room temp before shutting the stove down. Harman has a few trade secrets in there!

 

[dhall28]

this is a little bit of a misleading title imo, this scenario describes how someone can use more pellets than they were wanting to use, that is if they didn't know how to turn down there feed rate and/or turn down the temp dial. Beyond where the fan speed is set, all this comes into play way more when you put an OAK on your stove and start pulling in frigid temps, if you have your feed rate up and your temp dial down you can still start burning and putting much more heat into the room than desired.

 

[Ctcarl]

Good read .all I use is stove mode and never studied pellets usage due to fan speed.

 

[pell it]

350 to 500 degrees seems like a lot of heat going outside!!

 

[alternativeheat]

350 to 500 degrees seems like a lot of heat going outside!!

It is a lot of heat going outside but there are no creosote issues. And it's also a lot of heat going into the room in the case of the P61.

As to blower speed, that's about distribution of heat into the house. If you want to disperse heat further into the outreaches, then ya you use a high blower which sucks more heat from the stove of course. Additionally, don't think Room temp is void of this either, high fan uses more pellets yes. If you want to conserve on pellets, use less feed, less fan and lower settings, that simple. Enjoy the cold house ! If the house needs heat you need to burn pellets. Also in room temp mode if the house is really calling for heat you may find the stove on high fan anyway. Set your temp dial at 80 deg when the house is 64 and see what happens even at feed rate 4 and medium fan , bet it goes to high fan and a high flame..

 

[smwilliamson]

It's an older p61 but has the latest board. Red or black thermocouple isn't going to make any difference. Even if the board monitored the sweep of the fan setting knob it would have no way of knowing the heat transfer of the exchanger simply by monitoring only one sensor in the exhaust. If that were the case, how would their programming take in to account the variances in BTU output of different grades of pellets or whether the stove was clean or dirty? In room temp there is another sensor monitoring the room this giving the board more data to work with. In either mode I know that if the exhaust temp breeches 500 degrees the stove will bypass the sweep of the fan speed and toss the blower on high to cool the stove down but that is the only scenario where the fan speed is manipulated by the control board on stove temp

 

[mcerk02]

Harman stoves have two modes of operation, "stove temp" and "room temp". By turning the mode knob either up or down you select your mode. This knob is a multifunctional knob as it not only changes between the two operating modes but it also adjusts the fan speed for the distribution blower.

In the room temp mode the stove is monitoring the room temperature via the room thermistor probe. As the room cools or becomes warmer the stove is able to monitor progress and modulate the stove's heat output to ramp up or down the feed to meet demand respectively. Regardless of the distribution fan setting, the thermistor probe will control the stove's output, even ultimately turning the stove on or off as required.

If you choose to run the dove on the "stove temp" mode, the only sensor controlling the stove is the ESP (exhaust sensing probe). Stove temp mode uses the numbers 1 through 7 on the inside of the temperature dial. In this mode the stove is seeking to achieve and maintain an exhaust temp between 350 degrees (#1) and 500 degrees (#7). Here's the issue....

The mode selection knob still allows the user to control the distribution blower but the stove does not know what setting the blower is at. The amount of heat that is extracted from the heat exchanger varies according to how much room air is being transferred; the higher the fan setting, the more heat that is removed from the exhaust, thus will affect the ESP reading.

If you run in stove temp, simply adjusting the room distribution fan up will cause the stove to consume more pellets!

Here was my test on my P61 using 40lbs of LaCrete pellets in two separate runs:

First run was on Stove temp mode setting #5 moderate fan (middle), 40 lbs in about 12 hrs

Second run was on stove temp mode setting #3 with fan on high (all the way up), 40 lbs in about 9 hrs

Even though I adjusted down my heat setting, as the manual would suggest, I got less burn time out of 40lbs by using the high fan setting.

For both runs my feed rate was set to 4

I had always wondered about this scenario and finally got a moment of clarity over the weekend when I filled the hopper Friday about 7pm and at 8 the next morning it was empty and sputtering out. I filled it again but this time turned the fan up and kicked the heat setting down...by 6 that night the stove was completely out again.

I've had many customers over the years complain that for whatever reason, the stove just chews through pellets at times and at other times seems fine. It was always my assumption that this was the culprit....so no longer a myth.

Any of you out there care to back this theory I'd love it...especially someone with hardwood pellets, though I don't know if that would really make a difference.

I can agree with you that running the fan speed will cool down the stove and therefore it will feed more pellets to keep it up to temperature, but the fan is what is putting the heat in and distributing it into your house, after all, that's why the stove is there, running the fan on a lower speed is allowing more heat to stay in the stove and get wasted going to the outside, imagine if you had no fan at all, stove would consume less pellets but you would get very little heat distributing throughout the house.....I use both room temp and stove temp, stove temp when its really cold out and I know the stove wont even come close to shutting down due to being in room temp mode (P61A). I use room temp when its milder out, stove will cycle up and down as it needs to keep the house at a steady temp, although, I do see a design flaw once the house gets to the target temp, the stove will turn the fan off completely and just maintain, stove burns pellets with no fan running, this to me is wasteful, I am getting little benefit from all that heat inside the stove, It would be more efficient if it at least kept the fan on low at this point....

 

[johnchap]

stove temp for me , adjust fan accordingly ... room just cycles the whole thing way too often and most likely contributes to igniter failures .... just a theory ... my stove that I run constant ...is in sunroom and needs to pump heat ..