Connecting Wood Boiler To Oil Boiler

[mattd860]

Hi everyone. I just purchased a Harman SF-160 wood/coal boiler to supplement the oil boiler ((broken link removed to http://www.harmanstoves.com/products/details.asp?cat=central-heating&prd=boilers&f=BLRSF160)). The Wood Boiler will be placed into my attached garage, about 25 feet away from my oil boiler located in the basement. I'm having trouble figuring out the best method for connecting the two boilers because my goal is to keep my oil boiler 'hot' since my oil boiler has the domestic hot water coil. Otherwise, I would just bypass the oil boiler altogether like many of the diagrams show on this forum.

The directions (posted below) instruct me to run a pipe from the oil boiler return to the wood boiler return and then run another pipe from the wood boiler supply to the oil boiler supply. This should create a constant loop between the two boilers keeping the oil boiler hot for the three heating zones plus the domestic hot water.
This is option #2 that I've posted a picture of below.

However, will it be better to run a pipe from the wood boiler supply to the oil boiler return and then run another pipe from the wood boiler return to the oil boiler supply? With this option, the full amount of hot water from the wood boiler will always run through the entire boiler. With option #2, SOME of the heated water from the wood boiler will bypass the oil boiler. I'm concerned that this will prevent the domestic coil in the oil boiler from staying heated during a long shower on a cold day (when all zone circulates are on).

Here are some diagrams:


From Boiler Manual:

Option #1:

Option #2:

 

[Dune]

When I started to design my system I had similar intensions even though I had a stand alone DHW heater.
The problem is that the oil burner acts as an outdoor radiator, wasting your heat up the flue. Change your system so you don't need the coil in the oil burner, hook the two units in paralel and you will be much more efficient.

 

[mattd860]

Wow very good idea! I will certainly look into this. Thanks!

 

[b33p3r]

This has been my first year with my wood boiler and I piped it the way you are proposing. The flow is supply from wood boiler goes into return of oil boiler, the supply from the oil boiler goes to the return of wood boiler. The wood boiler to and through oil boiler circulates as long as wood boiler supply temp is > 150*. I also included some relay control to prevent oil boiler from ever firing if wood boiler is circulating to oil boiler. It has served me well. Does this get me the most out of the wood boiler? Probably not from what I read but it was definately the cheapest way to get me heating my house with the DHW coil in my boiler. I have no complaints but will look to improve in years to come.

 

[NYEDGE]

I also piped mine as you have in option one with a an additional circulator pump at the return line of the oil boiler that has the supply from the wood boiler.
While you can argue that you do have heat loss in the oil boiler from acting as a radiator, any such heat loss is inside your living space.
Piping this way also helps your oil boiler from being in a constant idle state, which means low temperatures. It has been explained to me that the low
temperature in a cast iron boiler jacket can cause condensation on the casting surface that leads to rust. A good quality/high efficiency oil boiler will have
plenty of internal insulation that will lessen the heat loss as well.

 

[mattd860]

I'm just curious to know why my boiler manual suggests Option #2. My father has had his Harman boiler installed like Option #2 for 20 years and it's working ver well.

 

[NYEDGE]

I'm just curious to know why my boiler manual suggests Option #2. My father has had his Harman boiler installed like Option #2 for 20 years and it's working ver well.

I will work either way just fine, but I went with option 1 because I wired my system so that if the temperature in the storage tanks drop below 140 degrees, the oil boiler will automatically start working when there is a demand. With option #2 you will have to manually start you oil boiler when it is needed. This may not be a problem for most of the time, but you may have some mornings that your storage temps have been depleted. I have only had one morning so far that the oil boiler kicked in because it was a snow day and I slept a little later.

 

[mattd860]

I'm just curious to know why my boiler manual suggests Option #2. My father has had his Harman boiler installed like Option #2 for 20 years and it's working ver well.

I will work either way just fine, but I went with option 1 because I wired my system so that if the temperature in the storage tanks drop below 140 degrees, the oil boiler will automatically start working when there is a demand. With option #2 you will have to manually start you oil boiler when it is needed. This may not be a problem for most of the time, but you may have some mornings that your storage temps have been depleted. I have only had one morning so far that the oil boiler kicked in because it was a snow day and I slept a little later.

I don't think I will have that problem since I currently have no hot water storage (not yet anyways). I plan on connecting the Oil boiler to a relay that will completely it off when the Wood boiler circulator starts pumping (when the wood boiler reaches 160°F). If I let the wood boiler die out and drop below 160°F, the oil boiler will be free to take over - I hope .

 

[Dune]

While you can argue that you do have heat loss in the oil boiler from acting as a radiator, any such heat loss is inside your living space.

Not really. Anytime the wood boiler is entirely supplied demand, the oil boiler is venting heat right out it's flue, NOTinside your living space.

 

[Dune]

I'm just curious to know why my boiler manual suggests Option #2. My father has had his Harman boiler installed like Option #2 for 20 years and it's working ver well.

I will work either way just fine, but I went with option 1 because I wired my system so that if the temperature in the storage tanks drop below 140 degrees, the oil boiler will automatically start working when there is a demand. With option #2 you will have to manually start you oil boiler when it is needed. This may not be a problem for most of the time, but you may have some mornings that your storage temps have been depleted. I have only had one morning so far that the oil boiler kicked in because it was a snow day and I slept a little later.

Why would you have to manualy start the boiler?

 

[NYEDGE]

I'm just curious to know why my boiler manual suggests Option #2. My father has had his Harman boiler installed like Option #2 for 20 years and it's working ver well.

I will work either way just fine, but I went with option 1 because I wired my system so that if the temperature in the storage tanks drop below 140 degrees, the oil boiler will automatically start working when there is a demand. With option #2 you will have to manually start you oil boiler when it is needed. This may not be a problem for most of the time, but you may have some mornings that your storage temps have been depleted. I have only had one morning so far that the oil boiler kicked in because it was a snow day and I slept a little later.

Why would you have to manualy start the boiler?

Option 2 diagram says "boiler manual"

 

[mattd860]

Option 2 diagram says "boiler manual"

When I wrote "boiler manual" I was just noting that Option 2 was directly copied from the boiler "instructional/install manual". The only "manual" part of my system will be to load the wood or coal and to pick up the phone and cancel my automatic oil delivery

 

[b33p3r]

The biggest reason I went with option 1 is because my DHW is through the oil boiler. By always circulating the wood boiler through the oil boiler, it maintained the DHW. I'm not sure how option 2 would maintain the DHW if the oil boiler was shut down.
Also as far as heat up the OB flue, there is no more heat lost up the flue as when the oil boiler was primary heat and was sitting idle.

 

[Dune]

The biggest reason I went with option 1 is because my DHW is through the oil boiler. By always circulating the wood boiler through the oil boiler, it maintained the DHW. I'm not sure how option 2 would maintain the DHW if the oil boiler was shut down.
Also as far as heat up the OB flue, there is no more heat lost up the flue as when the oil boiler was primary heat and was sitting idle.

True, except if you bypass the oil burner by installing in paralell rather than series, then no heat is lost up the flue.

 

[mattd860]

The biggest reason I went with option 1 is because my DHW is through the oil boiler. By always circulating the wood boiler through the oil boiler, it maintained the DHW. I'm not sure how option 2 would maintain the DHW if the oil boiler was shut down.
Also as far as heat up the OB flue, there is no more heat lost up the flue as when the oil boiler was primary heat and was sitting idle.

My father has his boiler setup using Option #2 and his DHW coil in the oil boiler never gets cold. However, I think instructional manual suggests option #2 so the hot water from the wood boiler can actually bypass the oil boiler in case there was a mega demand from all the zones. I only have 3 heating zones, no boiler mate, no hot tub, and no storage tank so even if all my zones (circulator pumps) are on, the hot water from the wood boiler should never completely bypass the oil boiler.

I still haven't decided which route to take yet. I would like to follow the install manual as well as replicate my fathers' setup but that little voice inside my head is telling me to go with option #1............

 

[EffectaBoilerUser (USA)]

I have recently helped 2 different people with the installation of 2 different brands of gasification boilers (eko 40 and effecta lambda 35) and both are very happy with how the boilers automatically switch between wood heated water or propane heated water. We are doing this WITHOUT going through the gas boiler BUT are using all of the existing gas boiler zone valve controls.
I have attached a drawing which shows how this is done.

Let me know if you have any questions.

EBU

 

[mattd860]

I have recently helped 2 different people with the installation of 2 different brands of gasification boilers (eko 40 and effecta lambda 35) and both are very happy with how the boilers automatically switch between wood heated water or propane heated water. We are doing this WITHOUT going through the gas boiler BUT are using all of the existing gas boiler zone valve controls.
I have attached a drawing which shows how this is done.

Let me know if you have any questions.

EBU

Ok that is essentially the same setup as option #2 as shown in the install manual. I've settled on going with the option #2 hookup and I will post some pictures of the setup once it's complete. Thanks!

 

[b33p3r]

My 2 biggest questions with option #2 was and still is, 1. If there is no heat zone turned on, does the water from wood boiler flow backwards through oil boiler to return to wood boiler?
2. If I'm getting set for a nice hot shower, and suddenly all 3 heat zones turn on, is there any flow through oil boiler to maintain DHW or are all the zones taking heated water from wood boiler leaving no flow through oil boiler? Typically an oil boiler will shut down all heat circs if temp dips too low. Leaving the oil boiler to recover while still supplying DHW.
Either way, if you do not have a indirect water tank for DHW, you must have flow through oil boiler. Thus standby losses up the flue although I doubt they are that great. But I agree they are there none the same. But even with option #2, hot goes to cold so what prevents you from losing heat back towards the oil boiler at the supply/return T's.
The lack of answers to these 2 questions is what prompted me to run directly through oil boiler.

 

[mattd860]

My 2 biggest questions with option #2 was and still is, 1. If there is no heat zone turned on, does the water from wood boiler flow backwards through oil boiler to return to wood boiler?
2. If I'm getting set for a nice hot shower, and suddenly all 3 heat zones turn on, is there any flow through oil boiler to maintain DHW or are all the zones taking heated water from wood boiler leaving no flow through oil boiler? Typically an oil boiler will shut down all heat circs if temp dips too low. Leaving the oil boiler to recover while still supplying DHW.
Either way, if you do not have a indirect water tank for DHW, you must have flow through oil boiler. Thus standby losses up the flue although I doubt they are that great. But I agree they are there none the same. But even with option #2, hot goes to cold so what prevents you from losing heat back towards the oil boiler at the supply/return T's.
The lack of answers to these 2 questions is what prompted me to run directly through oil boiler.

1. Yes - if no heat zone is turned on, water does flow backwards as indicated in Option 2.

2. With correct pump and pipe sizing, there should always be enough water to flow through the boiler even when all 3 heat zones are turned on.

 

[coal boiler]

my slant fin the circulator is on out let this goes to all my radiators then when return back goes through zone valves .then into bottom of my coal boiler out top then into return of oil boiler .series circuit.on return pipe before oil boiler i have three valves one directs return water into wood boiler this is the center valve two outer are for shutting wood out complete when burning wood coal outer valves open and center closed.when not in use opposite.i had originally hooked up tandem tee on bottom tee on top did not work well one boiler was diff temp all time.then i have separate zone just for cool down when goes over 200 half capacity of my boiler 40 gall dump zone.stainless steel chimney makes hugh diff for draft and high limit temp staying down.system has been in use 2 years now no problem works great.when i shut stove down close outer valves open center for return back to oil fired boiler

 

[DogDoc]

I am dealing with this very issue in another thread. See https://www.hearth.com/talk/threads/help-with-northland-boiler-w-1010.102556/. My DHW coil is within my oil boiler.

Perhaps some of you (Dune, Matt, NYEDGE) could tell me if there is something I can change in the plumbing of my system.

 

[91LMS]

when i installed my boiler i did option 1 where my domestic coil was in my oil boiler. to move towards a more efficient set-up i have since installed a boilermate. if i had it to do all over again (which i will in the spring) i will go with option 2 and also add storage. with a high heat demand my boiler works hard to overcome the heat loss from the oiler boiler to feed heat loads when dumping into the return water of the fossil boiler. not to mention when i look out my second story window over at the chimney used for the oil boiler i see a constant stream of heat venting outside.....

 

[Ldl0431usmc]

I have done quite a few installs and I'm fussy about efficiency and automation. Attached is a sample drawing of how I would pipe it (option 3?)

 

[Paso]

Glad to see this piping debate still rolls on

I have change my piping a few times looking for the "best" way.

I then realized i had to create what was best for me and how I wanted to operate and when I wanted to operate.

Some of you guys are Happily Married to your wood boiler as was I, then I wanted to divorce myself from spending so much time feeding the wood boiler, and never wanting the oil boiler to drink that high priced oil.

My system operates in extremely cold part of the country and there can't be any room for error or you have a block of ice.

I ended up piping from the wood boiler supply to the oil boiler supply thru to my zones then returning to the wood boiler.

This allowed the OWB to be the main source of heat production then if i was away or late and the system water cooled enough to cause the otherwise idle oil boiler to fire up and be the main source of heat ( read freeze protection )

My next project is to have the OWB heated by an WMO converted boiler piped to the HHO oil boiler then to a gas powered boiler to the zones then back to the OWB.

Then I can go away knowing ( read vacation) that the WMO boiler would have to quit the HHO boiler would have to quit and the natural gas boiler would have to quite before my building was to freeze.

Yes if the Hydro power goes down it will all freeze ( if it wasn't for my 12 volt powered oil burner ) That I have to rig up to automatically know to fire when the power is out.

I no longer concern myself with what piping will work better, think out what works best for you

 

[R Mannino]

I have done quite a few installs and I'm fussy about efficiency and automation. Attached is a sample drawing of how I would pipe it (option 3?)

What does your wiring and control strategy look like? That is true primary secondary piping and probably the best way to do it, storage is the only thing missing.