# Harman PB105 Pellet Boiler - In Series vs In Parallel



## wpessin (Dec 21, 2007)

Greetings...I just purchased a Harman PB105 pellet boiler to "add on" to my existing oil boiler.  I am trying to determine what the pros/cons would be for doing an in-series install versus an in-parallel.  The in-parallel is a bit more expensive since it requires cutting into the oil boiler's in and out pipes and adding a balancing valve on the oil boiler's out connection.  The in-series is more simple as it only ties into the oil boiler's return (in).  Is it worth paying more money for an in-parallel setup?

I only plan on using the pellet boiler during the late fall through early spring timeframe, and then the oil boiler during the warmer months for domestic hot water only.  In the in-parallel set-up, I can shut off the flow to the pellet boiler when it's not in use, versus the in-series where  the oil heated water would flow through the dormant pellet boiler.

Would be interested to hear other's experiences and thought on this.

Thanks!


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## Nofossil (Dec 21, 2007)

wpessin said:
			
		

> Greetings...I just purchased a Harman PB105 pellet boiler to "add on" to my existing oil boiler.  I am trying to determine what the pros/cons would be for doing an in-series install versus an in-parallel.  The in-parallel is a bit more expensive since it requires cutting into the oil boiler's in and out pipes and adding a balancing valve on the oil boiler's out connection.  The in-series is more simple as it only ties into the oil boiler's return (in).  Is it worth paying more money for an in-parallel setup?
> 
> I only plan on using the pellet boiler during the late fall through early spring timeframe, and then the oil boiler during the warmer months for domestic hot water only.  In the in-parallel set-up, I can shut off the flow to the pellet boiler when it's not in use, versus the in-series where  the oil heated water would flow through the dormant pellet boiler.
> 
> ...



Welcome to the site and to the boiler room. There have been many threads which touch on your question. My personal opinion is that parallel is the way to do it. I don't see the need for the mixing valve that you mention. In my case, I used a separate circulator with built-in check valve for each boiler. Parallel allows yoou to isolate (and even replace) either boiler without draining the system or even interrupting heat to the house.

I have an explanation of my system with diagrams on my site - link is below in my signature.


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## Eric Johnson (Dec 21, 2007)

Great to have a pellet boiler owner in the Boiler Room, wpessin. I believe you're our first, but definitely not the last. Welcome.


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## Jim Post (Dec 21, 2007)

When I piped my system, I  went with a series arrangement to avoid buying another pump....my wood boiler supply and return connect into my lp boiler's return using closely spaced Tees.  I have a pump on the return to my wood boiler and the original pump on the return to my lp boiler.  The pump on the wood boiler runs anytime the wb temp is over 140...so pretty much 24/7.  The pump on the lp boiler runs anytime one of my three hot water baseboard zones calls for heat.   I have ball valves on the wb supply and return lines so that I can isolate the wood boiler if I am going to be using lp for an extended period (out of town or laid up).  If you send your hot water through an unfired boiler...it will act like a radiator and send a % of your hard earned wood heat up the flue.  We hang lots of wet clothes around the lp boiler to take advantage of these standby losses.    When I redo my piping I am going to go to a primary/secondary scheme that will require another pump...but by my estimation I can replace my two bell and gossett pumps and add a third high efficiency pump and reduce my electrical consumption significantly.


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## Bartman (Dec 22, 2007)

My boiler configuration is series with 3 valves and has been great for 22 yrs. This fall I replaced my oil boiler and maintained the series setup. When I want only oil, open 1 close 2, when I want wood, open 2, close 1. Here is a picture of mine, I don't know if it will show all the piping


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## Bartman (Dec 22, 2007)

If you look closely, you will see the valve below the expansion tank on the right is closed, that the wood boiler supply running to the oil unit's return. To the bottom middle of the picture is the wood boiler's return valve that too is closed since I wasn't running on wood when the picture was taken. To the left of the photo next to the elbow going down is the return valve for the oil unit, that is open. When that is closed, it forces the circulator return to the then open valve to the wood boiler's return, supply from the wood boiler is then routed through it's open valve to the other side of the oil unit's closed return valve. If my wood unit can't supply enough heat whe all 4 zones are running, the oil boiler will kick in for a minute to help out.


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## wpessin (Dec 23, 2007)

Thanks for the responses so far.  The challenge I'm having is that I can't seem to find a plumber or HVAC specialist that really knows how to do this.  I've had 5 "experts" come look at the system and provided each with an install manual.  The quotes I've received range from about $600 to $6500.  Not exactly a tight range.  The guy who wants $6500 suggests all sorts of automation to control the flow between and through the systems.  The guy quoting $600 said I don't really need anything for the series set up except a cutoff valve with backflow prevention and of course some piping.

According to Harman (the manufacturer) when hooking this up either in series or in parallel, the pellet boiler can use all of the "services" of the oil boiler (expansion tank, blowers, zone controls, etc.) so it seems to me that this should be relatively straight forward, and certainly not something that should cost more than the boiler itself.

Any additional advice is greatly appreciated!


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## Nofossil (Dec 23, 2007)

Bill Pessin said:
			
		

> Thanks for the responses so far.  The challenge I'm having is that I can't seem to find a plumber or HVAC specialist that really knows how to do this.  I've had 5 "experts" come look at the system and provided each with an install manual.  The quotes I've received range from about $600 to $6500.  Not exactly a tight range.  The guy who wants $6500 suggests all sorts of automation to control the flow between and through the systems.  The guy quoting $600 said I don't really need anything for the series set up except a cutoff valve with backflow prevention and of course some piping.
> 
> According to Harman (the manufacturer) when hooking this up either in series or in parallel, the pellet boiler can use all of the "services" of the oil boiler (expansion tank, blowers, zone controls, etc.) so it seems to me that this should be relatively straight forward, and certainly not something that should cost more than the boiler itself.
> 
> Any additional advice is greatly appreciated!



I'm with the $600 guy on this one. It's simplified considerably if you'll only use one at a time. Backflow prevention and shutoff valves are about it under those conditions. You might need a larger expansion tank, though, because of the increased water volume in the system.


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## Bartman (Dec 24, 2007)

Expansion tanks are inexpensive and are required between the boiler and any valve. If you decide to run on pellets and you fire up your boiler for the first time in a while, and you have other things on your mind, (as we get older this tends to happen), you could possibly forget  to open your valves to the rest of the system. The expansion tank will give you that small buffer/time before the relief valve blows. Always us the largest expansion tank on a wood or coal boiler, it helps when power fails also.


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## rbeauli (Jan 15, 2009)

wpessin said:
			
		

> Greetings...I just purchased a Harman PB105 pellet boiler to "add on" to my existing oil boiler.  I am trying to determine what the pros/cons would be for doing an in-series install versus an in-parallel.  The in-parallel is a bit more expensive since it requires cutting into the oil boiler's in and out pipes and adding a balancing valve on the oil boiler's out connection.  The in-series is more simple as it only ties into the oil boiler's return (in).  Is it worth paying more money for an in-parallel setup?
> 
> I only plan on using the pellet boiler during the late fall through early spring timeframe, and then the oil boiler during the warmer months for domestic hot water only.  In the in-parallel set-up, I can shut off the flow to the pellet boiler when it's not in use, versus the in-series where  the oil heated water would flow through the dormant pellet boiler.
> 
> ...


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## AndrewChurchill (Jan 15, 2009)

I have a PB105 and I plumbed it in parallel.  I think it's the better way to go.  I can't see you paying $6500 to install it with your boiler.  I would think $1500 would be the max based on how my plumber set it up.  

There are several people on this board who have the PB105, Wil, StephenMoore, and Pearlset just to name a few.

Welcome aboard and I think you'll like the PB once it's installed and you get used to running it.


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## Sting (Jan 16, 2009)

A couple of folks with Traegers also!


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