- Nov 7, 2014
Thanks Mod for correcting the title!
Now, let's have some fun and stay warm!
How your stove works - The facts are pretty straightforward, but how you get people to properly interpret the facts is the hard part. It's your toy, run it the way you want as long as you understand what's going on behind the scenes! Everything noted below is based on me seeing what the stove is doing via the Harman diagnostic tool during the various operation methods. I get to see feed rates, max feed rates, current ESP temps, ESP set temps, room sensor temperatures, room sensor target temperatures, knob positions, switch positions, etc.
Here are the facts:
Stove temp - 100% driven the the ESP (temperature probe in stove exhaust flow). Temp dial corresponds to a fixed ESP temperature. For simplicity, let's assume a setting of 3 = 300 degrees ESP temp. The stove will ramp feed up/down to always be as close to 300 degrees as possible. In stove temp the stove doesn't care what the room temp is, only the ESP temp. The room might be 60 or 90 degrees doesn't matter, all it cares about is maintaining an ESP temp of 300.The stove will not shut off in stove temp regardless of whether the igniter switch is set to auto or manual. Stove temp, switch to manual - I call this fireplace mode. Distribution fan will not turn on unless the temp knob is set to 5 or higher. This is designed to give a nice fire, but not a ton of heat in the room. Most goes up the chimney. Stove temp, switch to auto - distribution fan operates normally to push heat into the room, regardless of stove or room temperature. There is a caveat to this, if you have your room temp set to 1 (very low) then the distribution blower might shut off because the ESP temperature is below the lowest setting allowed for the distribution blower to run.
Room Temp - The stove is 100% driven by the room temp sensor. The stove will automatically adjust feed and ESP temp to achieve the room temp set point. Once the set point is reached, the stove will slowly throttle up/down to maintain temperature. If it's 20 degrees outside, your heat load is high and the stove will feed more pellets to get the ESP temp hot enough to maintain room temperature set point. If it's 60 degrees outside, the stove will feed as little as possible and keep as low an ESP temp as possible to maintain room temperature. Igniter switch to manual, stove will go into maintenance burn in between calls for heat - prevents igniter cycling, might use a few more pellets in this mode...maybe... Igniter switch to auto, stove will initiate the shut down process in between calls for heat - igniter could cycle several times per day, depends on set point and heat load. If there is a call for heat during the shutdown process, the stove will start feeding pellets provided that the ESP temperature didn't go below the low limit. So, on really cold days, the stove might not shut off, even if it's on auto.
The key to getting room temp to work is placement or "calibration" of the room temp sensor. This is a tricky subject due to the sheer number of variables that can contribute to success or lack there of. Ideally, you want the tip of the probe in an area that is not subject to drafts, direct sun or areas that could lead to heat soak from the stove or areas that make it tough to calibrate like basement concrete floors. Ideally, you want the probe on an inside wall (no drafts), away from concrete and fairly far from the stove, even if you need to extend the wire. If the probe is where you are, then the stove can work to keep an even temp that works for you. If your set on having the dial temp correspond with the room temp, you will need to experiment for a while until you find the most reliable place for the probe to stay.
Alternatively, you can place the probe in a "stable" location and simply adjust the temp knob to achieve the most comfortable room temperature. Maybe 78 on the temp knob gives you a steady 72 degrees, no worries, just keep in mind that the probe reads 6 degrees high and do the simple math if you feel like adjusting the temp.
Either way, you need to be smarter than the probe, since it does nothing more or less than reading the temp where it resides.
If either option above doesn't suit your needs, you can ditch the way Harman wants you to run the stove and install a simple thermostat to control the room temperature. See my signature for details on the Skytach model or see post #8 below or the traditional Harman recommendation.
Feed Rates - Feed rate is controlled by the stove ESP. The stove will select a feed rate based on the actual temperature and target call for heat. The larger the temperature delta (actual room temp vs. target room temp), the greater the feed rate will be. 10 degrees would be a large delta and the stove would feed to reach max ESP temp of about 500 degrees depending on stove model. A 2 degree delta might only result in a feed rate of 20 seconds per minute even though the feed rate max dial is set to 4 (or 40 seconds per minute). The stove can vary the feed rate between 2.5 seconds per minute and the max feed rate you set. A feed rate of 6 would represent continuous feeding if the ESP wasn't seeing sufficient temperatures to satisfy the call for heat.When up to temp the stove will regulate itself form 2.5 seconds per minute of feed up to the limit you set.
Feed rates can lead to incomplete combustion comes in 2 forms:
1. Pellets spilling over the edge of the burn pot before they are reduced to ash.
Relative to #1 - when you run the stove wide open (stove temp setting at 7), the burning pellets should come no closer than 1 inch from the edge of the burn pot. You should have burning pellets and about 1" of ash before the edge. If pellets are bulging and close to the edge, you might not turn them to ash before spilling over the edge, wasting energy. If the burn line is too close, dial the feed rate back a bit, may by 1/2 of a number (i.e. 3.5 to 3). The stove doesn't run wide open once everything is up to temp, so this is only for scenarios where, for instance, the room is 65 and you want it 75 degrees or you turn the temp dial all the way clockwise (just don't walk away for too long or you'll bake yourself...).
Relative to #2 - smoke is also a sign of incomplete combustion, meaning that there is more fuel than air supplied by the combustion blower. This too should be evaluated when the stove is running WIDE OPEN. At night with a flashlight, you'll always see smoke. During the day, smoke is rated based on opacity or how easily you can see through it. Startup might be 50% opacity or fairly heavy smoke. If you are 10% or less (barely visible), that's reasonable and you aren't really wasting anything. If you have to struggle to see it, you're probably good. If you can easily see smoke and your flame is HUGE, try dialing back feed rate a bit to bring the air/fuel mix back into a more efficient range by dialing it back by 1/2 of a number (ie 3.5 to 3). In most cases, you don't want to be below 3 or much above 4. You'll also want to recalibrate after changing brands of pellets since the blend and size of pellet will cause it to burn/feed differently.
Setting your feed rate too low doesn't save pellets and stove performance will suffer since your inhibiting the ESP from reaching target temps. Setting your feed rate too low is like putting a brick underneath the gas pedal of your car.
Don't be tempted to set your feed rate too low.
So there's the facts, interpret away...
Cleaning tip - During your periodic cleaning, turn the knob to "test" while you clean the firebox to evacuate the ash out the chimney vs. into your room.
I have a 2008 p38+ that I just upgraded to the newer style circuit board. I use the Stove Temp setting since it works better for my particular set up. I followed the recommended feed rate of 4 but it is very hot with a huge flame. I am now at feed rate 1 and the flame is smaller but it's still hot. Maybe I have a bad board or the potentiometer dials are off. Will play around more tomorrow. Thanks for the tutorial.