Fixing my PB105

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


Feb 24, 2021
Concord NY
Hey everybody.

When i bought my house in May of 2020, there was a Pb105 in the basement disconnected in the basement. It was apparently in good working order, but was vented wrong ( and poorly, from what I'm reading here), so rather than fix it, they just cut power and pulled the pipe. They also didn't clean it very well, the exhaust pipe was loaded with ash up to the ESP. and 2 cleanout rods were stuck. Took a month of cleaning and tinkering to get it firing up and burning like it should. the way they had it set up, I'm surprised they didn't burn the house down.

During this winter, my propane boiler was running non stop. Propane was killing me price wise, so i figured id hook the pellet boiler up and give it a shot.

First thing i noticed is its set up almost like a wood burner in a heating sense, when the unit is switched on, the circulation pump on the inlet runs 24/7. So basically, Id let the house get down to 60-61 (usually when i came home at night) flip the boiler on ( making sure it was clean, that was a learning process of many ignition explosions ;lol) and let it ramp up and burn till the house got to 69-70. shut the unit off, while leaving power on ( circ pump still running) let the house get back down to 60-61 around 12 hours later, repeat.

Id like to fix how this runs, because it worked really well, and was way cheaper than propane, but i didn't like the lack of safety features like no dump zone, or using dryer vent as a chimney, or the fact that I had absolute garbage draft, because he put a 2' vertical section outside after at least 4 ft of horizontal run.

so here's my plans.

Move it 15' down the wall, away from the window, so I can vent straight up, thru the soffit, and above the roof. Here's the current pics of how he's got it vented. the pipe coming off the stove itself is single wall dryer vent. obviously, id like to come straight up from the stove with Class B piping, in between the joists, out the wall with a thimble, and straight up thru the roof. The joists themselves are 14 wide, with 9" vertical between the top of the foundation and the bottom of the floorboard. Is that enough clearance with a wall thimble to vent it safely?

Fixing my PB105
Fixing my PB105
Fixing my PB105

My house is currently baseboard heat, single circuit. id like to wire up a relay to control the circulator pump So if I read the manual right, and understand from what I'm reading on here, the PB105 is designed to run 24/7, maintaining the water in the boiler at whatever temps you set with the min/max. if house calls for heat, circulator pump runs, cooler water enters boiler, boiler ramps up to meet demand, once demand is met, feeder slows, and maintains again. Is this correct?

Also for dump zone / overheat.

My plan for overtemp was to run some simple baseboards in the basement ( its unfinished ) and just have a BPS and a simple circulator pump on it, over temp or power failure will trigger the circuit to open and pump. This sound decent enough?

lastly, what did you guys run for vent pipe? Any tips, Cause Iwant this thing to run well, without the risk of burning my house down.

From the install manual:

NOTE: Only PL vent pipe wall pass-throughs and fire stops should be used when venting through combustible materials.
You will probably need 4". You cannot safely use B-Vent. It is designed & tested for use with natural draft gas appliances...
I have worked on these Harman Pellet boilers and they work very well! 4” diameter pellet vent such as Duravent or Selkirk is what you should use. If you do not go all the way up the side of the house you can use a 90 Deg and a Horizontal termination cap. However if it is windy there then it is best to go straight above the roof line with as few bends as possible. Make sure you take the exhaust blower out atleast once a year and clean the ash out in there and around the blades and the ESP probe. It gets very dirty in there! One person I know runs it all year because she heats the domestic hot water too and uses about 10 tons of pellets per year. There should be a pressure release valve on top of the boiler just like all boilers have for safety. Home Depot has them. I had to replace one because it was leaking.
Last edited:
Its honestly always breezy to windy up where my house is ( especially in winter) I'm on a high hill on the east side of Lake Erie. So up, 90, thru the wall, 90, and straight up is going to be my best bet
Its honestly always breezy to windy up where my house is ( especially in winter) I'm on a high hill on the east side of Lake Erie. So up, 90, thru the wall, 90, and straight up is going to be my best bet
Sounds good but replace the bottom 90 outside with a cleanout T so you do not have to go on the roof to get a brush in the outside section. :) been heating our old Wisconsin farmhouse with a PB 105 pretty much 100% since 2012. I brn 6 to 8 tons of pellets every heating season.

The boiler should self-regulate its water temperature using the max/min dials on the control panel. During the height of the season I have the min set at 170 degrees and the max at 180. You do not want the water temp to drop below 140 degrees generally to minimize condensation (and creosote).

The circulation pump should be controlled by the thermostat in your living area. If you set the minimum temperature pretty high, like 170, if gives the boiler time to ignite when the thermostat calls for heat so the temperature in the water jacket won't fall too low when cooler water comes in from the heating loop. This is not an instant heat source like an oil or gas boiler -- it needs a little time to ramp up.

My boiler is direct-vented through a wall on the leeward (east) side of the building. A friend has his pellet furnace vent exiting from the west side of his home, and I don't think he's so happy with that arrangement. I would opt for the east or south side if possible.

As for the exhaust fan, I burn hardwood pellets and get best results cleaning the fan every six weeks to two months. A clean fan produces quicker ignition and less likelihood of explosive lights. The boiler has a spring-loaded plate that yields to explosions; it will prevent damage but it will fill your basement full of smoke.
I had to check, but White00s10 and I had a similar thread going on in the boiler forum last winter. Some of my last post was redundant to content in the previous thread.

White00s10, can you tell us which igniter has, the finned one or the pressure igniter? The pressure igniter is a footlong tube under the hopper with a dedicated air pump. The finned igniter is tucked inside the burnpot housing, visible behind the access panel secured by two wingbolts.

As for draft, if you can get the boiler close to an exterior wall, you can vent it straight out like a high-efficiency propane furnace -- it is power-vented. My exhaust has a 6-foot rise from just above the basement floor followed by a 5-foot horizontal run through an exterior wall. As long as I keep the exhaust fan reasonably clean the fan is perfectly adequate to vent the boiler properly.
The pressure igniter was only used on the old PC-45 for igniting corn. :)
I knew a guy who had a couple of 105s, one with the finned igniter and one with the pressure igniter. He said the pressure igniter was a huge improvement. I was burning softwood blend pellets last winterand was consistently getting ignition a minute and 45 seconds after the start of the ignition cycle. It is an excellent system.
  • Like
Reactions: Don2222
I knew a guy who had a couple of 105s, one with the finned igniter and one with the pressure igniter. He said the pressure igniter was a huge improvement. I was burning softwood blend pellets last winterand was consistently getting ignition a minute and 45 seconds after the start of the ignition cycle. It is an excellent system.
Yes that is good, finned igniter usually takes 5 to 6 minutes!
Harman had changed to the pressure ignition system after they were having all of the issues with the burnpot in the PB105. I have the finned igniter.

If the OP is having issues with the boiler going "kaboom" upon startup, it could be that the burnpot is cracked or warped and the air is not moving past the finned igniter properly. I had several burnpots that were replaced under warranty because of this.
  • Like
Reactions: Don2222
Sorry for the late reply, I seemed to stop getting notifications about this thread on my email.

I have the standard finned ignitor. I was having a lot of ignition explosions initially, but with a good cleaning, the issue seemed to resolve itself. I'm still planning on moving the unit to a better location and running a proper chimney all the way up. if for anything, ill gain peace of mind that ill always have a decent draft in the event of power outages and it'll be up to code.

Unfortunately, the previous owner wired the circ pump to be on at all times when the unit is powered up. I've since purchased a zone valve relay that will allow me to wire it to the thermostat in the house and onto turn the pump on when there's a call for heat.

Currently, I've noticed that there's a hump in my burn pot right above the ignitor. I know these Harmann's are known for it.

Is the new weldment style burn pot any better? (Shown in pic)


  • Fixing my PB105
    18.9 KB · Views: 168
From my experience, the new style is better.
When I had the improved burn pot installed under warranty, the Harman dealer told me the replacement part retailed for over $700. He told me to heft it, and it was quite heavy considering the size.

There are aftermarket replacements out there that are quite a bit cheaper than that -- but are they as robust as the original? Not sure. Earth Sense has one, and I would trust them to sell a quality part because they are a Harman dealer. At least you can ask them if the aftermarket quality is equal to the factory part.
Here's an interesting question. If I'm going through all the trouble of moving the boiler and setting it up correctly, should I take the time and install an OAK while I'm at it? Can I even get an OAK for it anymore?
As for your plumbing. Im currently running the house as a single zone. Do you guys have mixing valves set up to keep the return water from dropping the firebox temp too much? Or is it really not that big of a concern as long as your min/max is set high enough. Its baseboard heating in a 1500 sq ft house, So i cant see the temp drop being too severe when the call for heat comes in
A mixing valve is probably a good idea since you have the finned igniter. As Don2222 said, it can take five minutes to light the pellets, which in turn take some time to generate significant heat.

IIRC, one boiler owner on the forum kept his igniter on "manual" -- that process keeps up a minimal feed of pellets so the fire never actually goes out. If you do that, though, I would make sure the overheat circuit is wired up dispense hot water to a dump zone -- maybe just hook it up to power the main circ pump.
Well, I got the hard part of the new chimney installed, just waiting on a few more pieces to put it together and hook the stove up. I also made my own fresh air intake out of 4" galvanized ducting. Its not real pretty, but its just an experiment to see how it runs for this winter. Only reason for such the high rise on the fresh air intake is because we get some really deep snow here in Buffalo, and I didn't want the intake to be buried in a 2' snow drift. All the plumbing parts are in, I'm planning on starting to tackle the plumbing aspect here in another week or two!

chimney.jpg cold air kit.jpg
Made a chute/ramp out of spare plywood and some 2x6x12's i had laying around.

Only money I got into it is the screws and the cost of the tarp. Picking up 4 Ton of pellets tomorrow from TSC.

Fixing my PB105