Plumbing oil boiler in parallel with pellet stove

[pelletz]

Hi Everyone,
Im new to this forum.
Im looking to tie my pellet stove to my oil fired boiler.
Currently looking for a heat exchanger to install in my pellet stove which i think will be the most difficult about this setup.
I was hoping to get some advice for you guys on how to do the plumbing. From what ive read so far it doesnt seem to difficult.
Some specs on my boiler:
Crown Industries BD178
Manual located here.
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Here is a picture of my setup.

As seen in the picture I have 3 zone valves and one circulator pump.
The pellet stove is a Harman P38 which is located by one zone baseboard.
My intention is to plumb into the zone located by the pellet stove and use the existing zone plumbing to circulate the h20 through the furnace.
I intend to use an aqua-stat at the pellet stove location the trigger the zone valve and circulator pump.
The main reason im going this route is because i have rooms on the other side of the house which are cooler then the side with the pellet stove. I also use the boiler for domestic hot water.

A few questions right off:
The existing piping is 3/4" copper. Im looking at purchasing a stainless steel coil which is about 150" long and 9mm od. will there be a flow issue with the change in the size of the pipe?

Id like to use the zone located in the living room to to circulate the h20 to the furnace and then circulate hot h20 to the bedroom zone. I might be over thinking this but will there be an issue with this? Or will the bedroom zone work as usual and send hot h20 through the baseboard as it is called for?

Will the hydronic system h20 actually heat the tankless heater coil ( installed in the boiler) for domestic hot water as well?

My pellet stove is located a floor above the boiler. Will this be an issue with circulating the h20 or is it irrelevant since i would be using the boiler circulator pump?

Thank you in advance for all the advice!

 

[ScotL]

I'm not a plumbing guy but I can tell you how my pellet boiler was connected to my oil boiler.

The outlet of my pellet boiler is connected with a T and manual shutoff to the inlet of my oil boiler and the inlet of my pellet boiler is connected with a T and manual shutoff to the outlet of my oil boiler. I personally think it should have been outlet to outlet and inlet to inlet but this seems to work. Besides, I'm not a plumber. What do I know?
There's an expansion tank on the pellet boiler outlet line and a circulator pump on the inlet of the pellet boiler that runs off the oil boiler aqua-stat (with a shutoff toggle switch above the boiler).

There were no changes to my zones or the oil boiler. All they did was loop the oil boiler into the output of the pellet boiler and that loop doesn't circulate unless the aqua-stat calls for it which turns on the circulator pump for that loop.
My domestic hot water will cause the aqua-stat to call for heat so yes, I heat my domestic hot water all year with my pellet boiler. All I have to do is leave the oil boiler switch off (the one you have on the right hand side of your oil boiler in that picture).

But, this is with a Harman PB105 pellet boiler. You're planning on doing this with a P38? That's not meant to be a boiler and modifying it with a water coil inside the stove wouldn't be a good idea. I've seen some other stove's where people have tried that and then they blame their pellets for not burning well when the problem is they've altered the air flow of the stove.

 

[kofkorn]

Not sure this is the best of ideas. The biggest issue I see is what happens to the water in the exchanger when your house isn't calling for heat? The water won't be circulating and it will boil inside of the coils. Your standard boiler shuts off when the water temperature reaches a certain temp (Typically around 180F). Unless you're planning on having the stove start and stop each time heat is called for, you could have some catastrophic results. If you do decide to go this way, make sure you haven't shut off your expansion tank on your system and that it is working very well. Most boilers run at about 30 PSI or lower. You could do some significant damage if you over-pressure the system.

Good luck!

 

[velvetfoot]

There's a guy that makes a conversion kit, but that's all I know:
http://crosslinkconversions.com/

 

[Bioburner]

There's a guy that makes a conversion kit, but that's all I know:
http://crosslinkconversions.com/

I sent a PM. Don't need to have as much heat as this subject seems to get in this section.

 

[ScotL]

See. That's good old fashioned American ingenuity right there. Someone saw a need and devised a way to make it work.
If you really want to do that, I would definitely looking into something like that recommended above because it's had so many other installs done already. It would be a lot better than trying to re-invent it yourself.

 

[pelletz]

Not sure this is the best of ideas. The biggest issue I see is what happens to the water in the exchanger when your house isn't calling for heat? The water won't be circulating and it will boil inside of the coils. Your standard boiler shuts off when the water temperature reaches a certain temp (Typically around 180F). Unless you're planning on having the stove start and stop each time heat is called for, you could have some catastrophic results. If you do decide to go this way, make sure you haven't shut off your expansion tank on your system and that it is working very well. Most boilers run at about 30 PSI or lower. You could do some significant damage if you over-pressure the system.

Good luck!

I intend to use an aquastat by the pellet stove which would turn the pump on and open the valve to circulate the hot water from the stove to the boiler.
It would not be triggered by the thermostat calling for heat. Ofcourse i would install a pressure relief valve at the pellet stove as a safety measure.

 

[pelletz]

I'm not a plumbing guy but I can tell you how my pellet boiler was connected to my oil boiler.

The outlet of my pellet boiler is connected with a T and manual shutoff to the inlet of my oil boiler and the inlet of my pellet boiler is connected with a T and manual shutoff to the outlet of my oil boiler. I personally think it should have been outlet to outlet and inlet to inlet but this seems to work. Besides, I'm not a plumber. What do I know?
There's an expansion tank on the pellet boiler outlet line and a circulator pump on the inlet of the pellet boiler that runs off the oil boiler aqua-stat (with a shutoff toggle switch above the boiler).

There were no changes to my zones or the oil boiler. All they did was loop the oil boiler into the output of the pellet boiler and that loop doesn't circulate unless the aqua-stat calls for it which turns on the circulator pump for that loop.
My domestic hot water will cause the aqua-stat to call for heat so yes, I heat my domestic hot water all year with my pellet boiler. All I have to do is leave the oil boiler switch off (the one you have on the right hand side of your oil boiler in that picture).

But, this is with a Harman PB105 pellet boiler. You're planning on doing this with a P38? That's not meant to be a boiler and modifying it with a water coil inside the stove wouldn't be a good idea. I've seen some other stove's where people have tried that and then they blame their pellets for not burning well when the problem is they've altered the air flow of the stove.

There are a lot of pellet stoves not intended to be a boiler but as velvet foot and bioburner mentioned there is crosslinkconversions who makes custom coils and piping for pellet stoves. Ill need to make sure i seal off the penetrations properly which shouldnt be all that hard.

 

[Former Farmer]

If you "customize" your pellet stove, your insurance may not cover any damages if you have any. Chances are that you would never have to worry, but just in case something does happen.

 

[Bioburner]

Anytime the stove runs the coil will have to have flow through it or snap crackle pop, KABOOM.

 

[pelletz]

Anytime the stove runs the coil will have to have flow through it or snap crackle pop, KABOOM.

I dont believe it would "snap crackle pop" if there is water in it that is not past boiling temp. It would always have water in it but it would not be flowing unless the aquastat temp setting triggers the pump and valve.

 

[David Oliver]

I've done this a number of times in both parallel and in series...

The series is much more fire out fault tolerant because if you are away and the pellet stove goes out, your regular furnace can take over. You might want to look at flow control devices so that you can get proper circulation.

If you do this in parallel you will have to put in check valves so that you don't get weird circulation patterns in your system. Also like mentioned above don't isolate one because if you don't have proper pressure release valving, you will have major repairs. Oh you may also have to add an additional pump to get this system to flow.

I would also put in a bypass loop at your pellet stove so that if you ever wish to remove it, you simply close two valves and open the bypass valve and you are still running.

Something else I would do since you are breaking into your lines is to put in valves and unions on your main boiler. There will come a time to remove the old and put in a new one and this will allow you to easily remove it and replace it without all the hassel. (I hate chasing dry felts).

Hope this helps.

 

[pelletz]

I've done this a number of times in both parallel and in series...

The series is much more fire out fault tolerant because if you are away and the pellet stove goes out, your regular furnace can take over. You might want to look at flow control devices so that you can get proper circulation.

If you do this in parallel you will have to put in check valves so that you don't get weird circulation patterns in your system. Also like mentioned above don't isolate one because if you don't have proper pressure release valving, you will have major repairs. Oh you may also have to add an additional pump to get this system to flow.

I would also put in a bypass loop at your pellet stove so that if you ever wish to remove it, you simply close two valves and open the bypass valve and you are still running.

Something else I would do since you are breaking into your lines is to put in valves and unions on your main boiler. There will come a time to remove the old and put in a new one and this will allow you to easily remove it and replace it without all the hassel. (I hate chasing dry felts).

Hope this helps.

Now that i think of it i think my set up is going to be series since Im tying into an existing zone and circulating the h20 back in to the oil burner. At the same time if the h20 temp drops because the pellet stove is not heating the oil burner will act as usual.
If im tying into the zone at the pellet location i dont anticipate making any changes at the boiler end aside from running low voltage wire to it to tie in the aquastat. Im trying to make this setup as simple as possible for obvious reasons.
Basically I want to use an existing zone to circulate the heated up h20 (by the pellet stove) back into the boiler.
I would use an aquastat at the pellet stove to trigger the pump and valve related to that zone.
This would in effect provide 180 degree temperature water in the boiler which would in effect heat the domestic hot water.
When a different zone calls for heat there would already be 180 degree water in the boiler ready to circulate into that zone.
This is all hypothetical of course.

 

[David Oliver]

Now that i think of it i think my set up is going to be series since Im tying into an existing zone and circulating the h20 back in to the oil burner. At the same time if the h20 temp drops because the pellet stove is not heating the oil burner will act as usual.
If im tying into the zone at the pellet location i dont anticipate making any changes at the boiler end aside from running low voltage wire to it to tie in the aquastat. Im trying to make this setup as simple as possible for obvious reasons.
Basically I want to use an existing zone to circulate the heated up h20 (by the pellet stove) back into the boiler.
I would use an aquastat at the pellet stove to trigger the pump and valve related to that zone.
This would in effect provide 180 degree temperature water in the boiler which would in effect heat the domestic hot water.
When a different zone calls for heat there would already be 180 degree water in the boiler ready to circulate into that zone.
This is all hypothetical of course.

Something else to remember...your control voltages may be different. I ran into this between my thermostat and a flew assist unit I wired up (one was 24V the other 12V).

Another item to think about looking into is perhaps some electric louvers for your furnace stack. This will stop the chimney from sucking all your heat out of the basement if you are circulating hot water through the boiler when heating with the pellet stove...but make certain that there are limit switches on it so that it's open before the furnace will fire.

 

[pelletz]

Something else to remember...your control voltages may be different. I ran into this between my thermostat and a flew assist unit I wired up (one was 24V the other 12V).

Another item to think about looking into is perhaps some electric louvers for your furnace stack. This will stop the chimney from sucking all your heat out of the basement if you are circulating hot water through the boiler when heating with the pellet stove...but make certain that there are limit switches on it so that it's open before the furnace will fire.

I actually have a direct/power vent for the furnace so i dont think draft will be an issue...
My background is electrical so im pretty confident in that aspect. I dont have much plumbing experience aside from soldering and running copper therefore i want to make sure i have all the correct fiitings/equipment installed to prevent accidents.

 

[SmokeyTheBear]

I dont believe it would "snap crackle pop" if there is water in it that is not past boiling temp. It would always have water in it but it would not be flowing unless the aquastat temp setting triggers the pump and valve.

If it is a closed system it had better have water flowing through thaa heat exchanger on the pellet unit or it will

I dont believe it would "snap crackle pop" if there is water in it that is not past boiling temp. It would always have water in it but it would not be flowing unless the aquastat temp setting triggers the pump and valve.

You will need a pressure relief on that setup, it makes no difference if there is air or no air in the line or if the fluid is moving or not the pellet stove will provide heat to the water or whatever fluid (gases including air are considered a fluid) is in the jacket attached to the stove as long as the stove is fired which at the very least will cause both whatever is in that line to expand causing a rise in pressure. It is the pressure rise that provides any possible boomy.

 

[pelletz]

If it is a closed system it had better have water flowing through thaa heat exchanger on the pellet unit or it will


You will need a pressure relief on that setup, it makes no difference if there is air or no air in the line or if the fluid is moving or not the pellet stove will provide heat to the water or whatever fluid (gases including air are considered a fluid) is in the jacket attached to the stove as long as the stove is fired which at the very least will cause both whatever is in that line to expand causing a rise in pressure. It is the pressure rise that provides any possible boomy.

If i have an aqua stat set at 180 on the pellet side wont it (in theory) circulate the water well before the pressure raises to an unsafe level?

 

[ScotL]

I can't say I know much about plumbing, but what I do know about steam (1600 to 1700 times the volume of the water it came from) is enough to make me nervous. I'd definitely follow Smokey's advice and make sure there was a steam rated pressure relief on the system.

Myth Busters:
Real explosion:

 

[Bioburner]

If i have an aqua stat set at 180 on the pellet side wont it (in theory) circulate the water well before the pressure raises to an unsafe level?

But the exchanger tubes can be dry and hence warped when the water changes to a nearly non conductive vapor.

 

[David Oliver]

I actually have a direct/power vent for the furnace so i dont think draft will be an issue...
My background is electrical so im pretty confident in that aspect. I dont have much plumbing experience aside from soldering and running copper therefore i want to make sure i have all the correct fiitings/equipment installed to prevent accidents.

I found that if the draft is strong enough the power vent fan will free wheel spin when off (no brake on the motor)...a convection break will be needed of one sort or another. This is only from my observations as to how my systems function. Having degrees in electrical and hydraulic engineering and I have designed many a makeup air system for kitchens, the math is the same in both, in fact all they do is change the names for the equations (Newton rules and all)...and in truth I think that plumbing came first then they only changed the names when the electrical science was found to follow the same math modeling of processes...same for kinematics (it's all a sum of forces).

As a test use an ammeter and see what your actual air flows are when the furnace is off vs on and you may be surprised about how much does go up the flue.

Good luck and have fun with this...It's a great project and you will learn a lot about your machines and their environment with so few going the extra mile (like you) and trying to improve/augment what others have done before.

 

[David Oliver]

But the exchanger tubes can be dry and hence warped when the water changes to a nearly non conductive vapor.

not only warp, but when steam goes dry the pressure goes up exponentially...and your boiler becomes an containment vessel not designed for a few thousand pounds of pressure.

 

[David Oliver]

If i have an aqua stat set at 180 on the pellet side wont it (in theory) circulate the water well before the pressure raises to an unsafe level?

an Aquastat is a temperature actuated relay...that then controls a circulation pump of some sort...a pressure relief valve in the system will protect it but you should also use this in conjunction with a Low Water Cut‑Off type device for further protection.

 

[David Oliver]

I intend to use an aquastat by the pellet stove which would turn the pump on and open the valve to circulate the hot water from the stove to the boiler.
It would not be triggered by the thermostat calling for heat. Ofcourse i would install a pressure relief valve at the pellet stove as a safety measure.

don't forget to include a drain for when the pressure relief blows (good planning)...the scope of the pic of the basement setup doesn't show that part... but I've seen lots of nasty water come out of those things and ruin lots of treasures when they do go. (They don't always actuate due to over pressure...)

If the new appliance is in your main living quarters, a flood up there does little for a happy household...just saying ;o)

 

[SmokeyTheBear]

If i have an aqua stat set at 180 on the pellet side wont it (in theory) circulate the water well before the pressure raises to an unsafe level?

Pellet stoves do not turn off on a dime and all closed systems need a pressure relief system. Your aquastat controls only the signal to a device and not the actual device, devices do not always:

1. Act upon a signal.
2. or when they do act may not shut a solid fuel device down fast enough. That pellet stove ain't a digital device, it can take a good deal of time to shut down.

My boiler like yours has both an aquastat and a pressure relief system, as does an electric hot water heater, or an indirect hot water system like what I have attached to my boiler.

There is a water jacket for attachment to a pellet stove that uses a passive open safety system, I believe but can't stay for certain that the crosslink system uses a pressure relief valve.

Take bioburner up on his offer to chat via private communication.

I'm going to add the standard disclaimer so everyone who reads this thread will understand the concerns and possible issues of adding any third party device to a pellet stove.

Unless the pellet stove you hook any third party device to has been certified to use that device you will no longer have a certified device and any representation to another party such as your insurance company is void.

This can result in various things happening that you might not want to have to deal with.

 

[Bioburner]

My crosslink has 2 PRVs., not including the electric boiler systems.