Oil boiler and outdoor Wood Boiler

Kkane97

I recently bought a Hawkin HE1100 225,000 btu wood stove and want to install it and feed my oil unit of the house. And primarily heat my garage

I want to use the owb to heat my garage, 54x36, fully insulated 12ft ceiling. And feed my indoor oil boiler through a heat exchanger on the return with two closely spaced tees 1 1/4 " pipe. When the zones inside aren't calling for heat, I was thinking I could use a zone valve and direct the owb source to the garage primarily and run it through two 50,000 BTU units I found locally. I don't mind if the indoor unit kicks on when the garage is heating as I work on the side from home in the shop. So just leaving my indoor unit set to 165 or so and just have a little longer zone run times when not heating with the owb. Or is there a better way to control the indoor oil boiler with a temperature differential to the owb if the outdoor stove cools down like the fire went low I want the oil to fire it it's core temp gets low.

On another post I believe we have identified a issue with the circulator location in my radiant zone so I will be changing some of the piping around and was wondering if using a water storage tank inside would be a good idea as well so I could have some buffer 

hot_rod

This Idronics issue shows piping and wiring concepts
most all the wiring schematics show a differential controller. It watches two temperatures to better control the different heat sources


https://www.caleffi.com/sites/default/files/media/external-file/Idronics_10_NA_Hydronics%20for%20wood-fired%20heat%20sources.pdf

leonz

If you want to save more fuel for your forest eater and do less work you should fill it half full of standard firebrick up to the flue breech which will absorb the heat from the wood fire and at the same time shed heat back into the fire box to make the fire hotter and burn the wood and smoke more effectively.

I did this with my old hand fed wood and coal boiler and I cut my wood and coal use by half.
By increasing the amount of thermal mass in your forest eater you will create a huge amount of useable energy by storing the heat in the firebrick.

GroundUp

Typically speaking, that exchanger just gets cut into the existing return line prior to re-entering the indoor boiler with no need for closely spaced tees. The circulator on the OWB runs 24/7 so that exchanger is always hot, and when any indoor zone is running, it will essentially preheat the return water entering the oil boiler via the aforementioned heat exchanger.

Is this garage attached or detached? If the former, maybe add it as a zone to your oil boiler so you also have backup? Otherwise just make a series or parallel loop out of it and hit all 3 exchangers at all times. If the latter, you'll want to run a separate loop from the OWB to that building also with its own circulator located on the OWB and just circulate 24/7 while controlling the fans with a thermostat. As for controlling the oil boiler, I would add an aquastat or Ranco type controller on the incoming OWB supply line at the heat exchanger and interrupt your oil boiler's TT signal with it, so that any time the OWB is above say 150*, the oil boiler will not fire. Whenever the OWB temp drops, the oil boiler will fire to make up the difference. If the OWB is something you don't intend to keep hot all the time during heating season, you may wish to have some sort of thermostatic bypass to prevent keeping the water jacket at oil boiler temp due to the 24/7 circulation of the OWB circ.

Regarding leonz, please disregard everything he/she said. It's 100% false.

hot_rod

Any time the OWF has energy to give, may as well use it

This piping allows both boilers to contribute to the load  until the delta T control senses the OWF is no longer able to add energy

Piping could be with closely spaced tees, the HydroLink is an option 

Kkane97

hot_rod said:

Any time the OWF has energy to give, may as well use it

This piping allows both boilers to contribute to the load  until the delta T control senses the OWF is no longer able to add energy

Piping could be with closely spaced tees, the HydroLink is an option 

What would I use to control the indoor circulators in relation to the OWB temp? The small shunt circulator in the diagram would be used only when the outdoor is up to temp?

Kkane97

GroundUp said:

Typically speaking, that exchanger just gets cut into the existing return line prior to re-entering the indoor boiler with no need for closely spaced tees. The circulator on the OWB runs 24/7 so that exchanger is always hot, and when any indoor zone is running, it will essentially preheat the return water entering the oil boiler via the aforementioned heat exchanger. Is this garage attached or detached? If the former, maybe add it as a zone to your oil boiler so you also have backup? Otherwise just make a series or parallel loop out of it and hit all 3 exchangers at all times. If the latter, you'll want to run a separate loop from the OWB to that building also with its own circulator located on the OWB and just circulate 24/7 while controlling the fans with a thermostat. As for controlling the oil boiler, I would add an aquastat or Ranco type controller on the incoming OWB supply line at the heat exchanger and interrupt your oil boiler's TT signal with it, so that any time the OWB is above say 150*, the oil boiler will not fire. Whenever the OWB temp drops, the oil boiler will fire to make up the difference. If the OWB is something you don't intend to keep hot all the time during heating season, you may wish to have some sort of thermostatic bypass to prevent keeping the water jacket at oil boiler temp due to the 24/7 circulation of the OWB circ. Regarding leonz, please disregard everything he/she said. It's 100% false.

The garage is detached, I will be feeding it with it's own piping in second outlet and return off it's tank was my plan and to wire a zone valve to switch between house and garage? Possibly set a way to choose one as a priority automatic switching

Would the owb side of the heat exchanger cause a significant loss of heat if the owb was cold but circulator was not running? With a check valve to prevent temperature caused flow through it?

hot_rod

Kkane97 said:

hot_rod said:

Any time the OWF has energy to give, may as well use it

This piping allows both boilers to contribute to the load  until the delta T control senses the OWF is no longer able to add energy

Piping could be with closely spaced tees, the HydroLink is an option 

What would I use to control the indoor circulators in relation to the OWB temp? The small shunt circulator in the diagram would be used only when the outdoor is up to temp?

The shunt circ is another way to do freeze protection. A thermostat on the supply from the OWF controls it so the indoor boiler could warm the OWF to 38 F or some  temperature adequate for freeze protection

The OWF would need to run 24/7 of course

This logic assures you use the least amount of the indoor boiler heat to prevent freezing, and also lessens loss from the OWF piping by keeping the temperature as low as possible for freeze protection 

hot_rod

Kkane97 said:

GroundUp said:

Typically speaking, that exchanger just gets cut into the existing return line prior to re-entering the indoor boiler with no need for closely spaced tees. The circulator on the OWB runs 24/7 so that exchanger is always hot, and when any indoor zone is running, it will essentially preheat the return water entering the oil boiler via the aforementioned heat exchanger. Is this garage attached or detached? If the former, maybe add it as a zone to your oil boiler so you also have backup? Otherwise just make a series or parallel loop out of it and hit all 3 exchangers at all times. If the latter, you'll want to run a separate loop from the OWB to that building also with its own circulator located on the OWB and just circulate 24/7 while controlling the fans with a thermostat. As for controlling the oil boiler, I would add an aquastat or Ranco type controller on the incoming OWB supply line at the heat exchanger and interrupt your oil boiler's TT signal with it, so that any time the OWB is above say 150*, the oil boiler will not fire. Whenever the OWB temp drops, the oil boiler will fire to make up the difference. If the OWB is something you don't intend to keep hot all the time during heating season, you may wish to have some sort of thermostatic bypass to prevent keeping the water jacket at oil boiler temp due to the 24/7 circulation of the OWB circ. Regarding leonz, please disregard everything he/she said. It's 100% false.

The garage is detached, I will be feeding it with it's own piping in second outlet and return off it's tank was my plan and to wire a zone valve to switch between house and garage? Possibly set a way to choose one as a priority automatic switching

Would the owb side of the heat exchanger cause a significant loss of heat if the owb was cold but circulator was not running? With a check valve to prevent temperature caused flow through it?

Kkane97 said:

GroundUp said:

Typically speaking, that exchanger just gets cut into the existing return line prior to re-entering the indoor boiler with no need for closely spaced tees. The circulator on the OWB runs 24/7 so that exchanger is always hot, and when any indoor zone is running, it will essentially preheat the return water entering the oil boiler via the aforementioned heat exchanger. Is this garage attached or detached? If the former, maybe add it as a zone to your oil boiler so you also have backup? Otherwise just make a series or parallel loop out of it and hit all 3 exchangers at all times. If the latter, you'll want to run a separate loop from the OWB to that building also with its own circulator located on the OWB and just circulate 24/7 while controlling the fans with a thermostat. As for controlling the oil boiler, I would add an aquastat or Ranco type controller on the incoming OWB supply line at the heat exchanger and interrupt your oil boiler's TT signal with it, so that any time the OWB is above say 150*, the oil boiler will not fire. Whenever the OWB temp drops, the oil boiler will fire to make up the difference. If the OWB is something you don't intend to keep hot all the time during heating season, you may wish to have some sort of thermostatic bypass to prevent keeping the water jacket at oil boiler temp due to the 24/7 circulation of the OWB circ. Regarding leonz, please disregard everything he/she said. It's 100% false.

The garage is detached, I will be feeding it with it's own piping in second outlet and return off it's tank was my plan and to wire a zone valve to switch between house and garage? Possibly set a way to choose one as a priority automatic switching

Would the owb side of the heat exchanger cause a significant loss of heat if the owb was cold but circulator was not running? With a check valve to prevent temperature caused flow through it?

How will you keep the garage tube from freezing if you use a zone valve to choose either house or garage, from the OWF?

GroundUp

You don't ever shut off flow to the garage. Both loops from the OWB must be flowing 24/7 and that is not negotiable. Each loop has its own circulator that runs continuously all winter.

Kkane97

Is it not worth the cost of glycol in the system? 

Kkane97

Would this be feasible break the return as shown below, reducing from 1 1/2 to 1" , 175000 btu heat exchanger, adding a circulator pump to run continuous through the heat exchanger from on the supply, or put it lower on the return side only? The line from supply with the circulator as the small shunt circulator in the posts above  and possibly a mixing valve to act as a boiler protection loop to prevent condensating?, or the other location without a tee from the supply?

hot_rod

A heat exchanger for the garage? If so that loop could be glycol, instead of glycol in the entire system. Then no need to run 24-7 on the garage zone.

Kkane97

Noah heat exchanger in the basement for the house, and the garage loop running through two hanging unit heaters . Two separate lines coming out the back of the boiler. Two separate circulator pumps

hot_rod

You mentioned taking the garage off the connections at the back of the boiler. Are the unit heaters above the level of the water in the boiler? It is an unpressurized boiler?

Kkane97

Yes the outdoor would be unpressurized, I was under the impression I could do the following

Glycol in the system for the OWB, two supply and returns, one feeding the house through a heat exchanger to the indoor oil boiler. And the other to two unit heaters mounted in the ceiling of the shop. Being there is glycol in the system I could leave the house side off if the garage was calling for heat and the oil would kick on as normal. If the garage is not calling for heat the OWB would circulate through the exchanger in the house.

hot_rod

You really don’t want glycol in an 
open system. It needs to be sealed away from oxygen or it will be compromised in a few months time

how many gallons does the system hold? Have you priced hydronic glycol?

Kkane97

That's makes sense, thank you. I know the price my tractor tires are full lol. I figured if I wanted to be able to turn the garage off it would just be an expense I had to put into the system. I did not mind because Don't always use it there will be several days during the week that is not used. So if I didn't have to burn I wouldnt

Kkane97

Basically this is what I have in my head, I drew it out can you help  me change this to a proper setup ? I forgot to add a pump and check for the heat exchanger line off the OWB

GroundUp

You could pipe it like that, but leave the check valves out of the OWB side- they're worthless. Also skip that wraparound pump on the indoor side unless you have a domestic coil in the oil boiler. Just let both OWB loops circulate 24/7 and control the fans on the unit heaters with a thermostat. No glycol, no BS. There is no need to shut the house off when the shop is running- they are designed to run both at the same time.

Kkane97

My thought was if I shut one zone off on the owb, I would need a check valve to prevent thermostatic flow.

Say I go away for a week and I don't want to run owb, the pumps just continuously running by themselves be enough to prevent freezing. It would be warming the owb through the heat exchanger all the time then by the oil boiler

GroundUp

But you don't shut off one zone/loop, ever. They both run 24/7 as required by the OWB. The pumps running does not always prevent freezing, but the backfeed from the oil boiler will- assuming everything stays running. If you're gone for a week it may cost you an extra $20-30 in oil, compared to thousands in glycol that needs to be replaced every few years due to breakdown in an atmospheric system.

hot_rod

If you had a hx in the shop you could use a shunt pump there also
The shunt and  control assures the least amount of oil will be used to keep the systems from freezing

You could run some numbers based on the volume of your owf  and expected temperatures, I suspect it will take more than a gallon of oil per day to just let the oil boiler heat the owf to some unknown high temperature
Plus it needs the capacity to keep the house warm also while it heats the ground and owf

Running the owf through the oil boiler all the time wastes energy up the flue also. It becomes a cooling tower for the owf🫢, when it is off cycle

So you spend wood $$ to keep the oil boiler hot, and oil to keep the owf hot?

A few basic piping changes make all those wasteful issues go away, or at least minimize them

I guess its your $$ to spend

Kkane97

GroundUp said:

But you don't shut off one zone/loop, ever. They both run 24/7 as required by the OWB. The pumps running does not always prevent freezing, but the backfeed from the oil boiler will- assuming everything stays running. If you're gone for a week it may cost you an extra $20-30 in oil, compared to thousands in glycol that needs to be replaced every few years due to breakdown in an atmospheric system.

Makes sense to me. 

Besides my crude drawing, is there something I should change before figuring out fittings to order?

I am planning on using this heat exchanger with 1 1/4 " ports

https://www.outdoorfurnacesupply.com/5-x12-brazed-40-plate-heat-exchanger-outdoor-wood-furnace-1-1-4-mpt.html

I need to add boiler drains for bleeding at the OWB side, flex connections for expansion in the underground pipe to the heat exchanger. The OWB will be feeding the house through roughly 75 ft of 1". 

Kkane97

hot_rod said:

If you had a hx in the shop you could use a shunt pump there also
The shunt and  control assures the least amount of oil will be used to keep the systems from freezing

You could run some numbers based on the volume of your owf  and expected temperatures, I suspect it will take more than a gallon of oil per day to just let the oil boiler heat the owf to some unknown high temperature
Plus it needs the capacity to keep the house warm also while it heats the ground and owf

Running the owf through the oil boiler all the time wastes energy up the flue also. It becomes a cooling tower for the owf🫢, when it is off cycle

So you spend wood $$ to keep the oil boiler hot, and oil to keep the owf hot?

A few basic piping changes make all those wasteful issues go away, or at least minimize them

I guess its your $$ to spend

So if it's better to use a shunt pump, which if I understand correctly, is a small circulator pump strictly for slightly warming the water returning to the OWB? Would my original design work for that? And doing the same thing in the shop side with a heat exchanger there as well

Kkane97

GroundUp

Why are we trying to reinvent the wheel? OWB loop through plate HX, and OWB loop through W2A HX in shop. 2 circulators. All done. Nothing else, unless you want a 3 way to bypass the plate to prevent backfeeding. Boiler drains are nothing but a potential leak point if the OWB side is properly installed. The HX size is completely dependent upon the heat load, but unless you can get away with 140* SWT to your radiation, 40 plates is not enough.

Kkane97

Just trying to figure the best way to set this up  is all.  The indoor boiler is 110,000 BTU and is slightly oversized for the heat load of the house. 

GroundUp

And I am offering you the proper way to install it, but we don't have all the details. If your radiation cannot heat sufficiently with 140 degree water on a design day, that heat exchanger is too small. Assuming 160 degree supply, I usually cut the BTU load in half. So if the load is 100k, you should have a 50 plate 5x12 at minimum.

Kkane97

GroundUp said:

And I am offering you the proper way to install it, but we don't have all the details. If your radiation cannot heat sufficiently with 140 degree water on a design day, that heat exchanger is too small. Assuming 160 degree supply

where have you gotten that from ? 

hot_rod

Kkane97 said:

Just trying to figure the best way to set this up  is all.  The indoor boiler is 110,000 BTU and is slightly oversized for the heat load of the house. 

As you have experienced, there is no one “correct” answer to your question.
When we wrote Idronics 12 we wanted to show piping and control options that went beyond the KISS method that manufactures and salespeople promote in the OWF industry.

This Idronics was used to present training to one of the largest OWF manufacturers in MN years ago. They wanted to learn other piping and control options. Not sure where they went with that information😗

Understand that the typical wood burner is looking for the least expensive method to get the job done. I get that, they are thinking to lower heating costs. I ran two wood burners on my farm for years for this very reason. It is a young man’s sport IMO.

The example I proposed hydraulically disconnects the loads and boilers. Flow only moves through the devices that are needed.
The extra shunt pump and control is to minimize the amount of flow and heat energy from the gas or oil appliance to get the freeze protection covered. Yes it is more $$ and more complicated to assemble.


Some owners appreciate the extra design, others still go with KISS.
The parts and pieces to do your system should be based on good industry design. What is the size of the load in the two buildings? What are the piping distances? What size underground tube? Is the boiler even adequate to cover one or both loads? Do you want automatic controls, or manual ball valves to shuffle loads?

It is harder to jump into the middle of a system and determine the best outcome without enough data for us to steer you

GroundUp

Kkane97 said:

GroundUp said:

And I am offering you the proper way to install it, but we don't have all the details. If your radiation cannot heat sufficiently with 140 degree water on a design day, that heat exchanger is too small. Assuming 160 degree supply

where have you gotten that from ? 


Decades of experience installing, and thousands of hours troubleshooting underperforming OWB systems.

Kkane97

Calculating the heat load of the shop  I'm not 100% on its 54x36, 12ft ceilings ,r21 walls r30 ceilings. 

The shop I have a 25 ft run from the OWB to the wall entrance and then roughly 50 ft of pipe I was planning between the two unit heaters. 

The house to the OWB is going to be roughly 75ft 

I have 4.5" case 1" diameter pex pipe, foam insulation. 

If  I were to go the complicated method, which would allow possibly to shut down the OWBfor extended periods of time I would like it to automatically switch pumps on as loads call for heat. 

Kkane97

GroundUp said:

GroundUp said:

And I am offering you the proper way to install it, but we don't have all the details. If your radiation cannot heat sufficiently with 140 degree water on a design day, that heat exchanger is too small. Assuming 160 degree supply

where have you gotten that from ? 

Decades of experience installing, and thousands of hours troubleshooting underperforming OWB systems.

Oh okay I understand. Thought you were referring to another post that I had where I thought my radiance system was not working as well as  it should. I recently converted one son of my house to staple up radiant. I was confused because I had not mentioned of a heat exchanger being present in my system already 

hot_rod

It depends on how cold it gets in your location. I doubt you could completely shut down the system in freezing conditions without draining it. @GroundUp may have an opinion on just circulating for freeze protection. The back of the heater and where the pipes come up from the ground is where I saw the most freeze up in power outage conditions in Missouri and Arkansas where I worked on wood burning systems. I suspect Minnesota would be much different.

What is the btu rating on the heater? How well is the fire controlled in that unit? A damper? Inducer fan? Some units ideal and ramp up better. Some burn out during extended no load conditions.

Kkane97

It is a model HE 1100 Hawkins 275,000 BTU has a blower fan  

hot_rod

A WAG in the shop load 40,000 btu/ hr, calling it 25 btu/ sq ft. I don’t know what the house load is, but you should have plenty of boiler capacity. Too much boiler and they tend to shut down often, possibly smolder much of the season. Oxygen starved conditions tend to create more emissions and smoke. Any neighbors close by, downwind?

At the very least consider my suggestion about primary secondary piping. It is this simple. Come off the HX with a short piece of 1-1/4 or 1-1/2” copper. That creates a hydraulic separation.
Then tee in your existing circulators to those branches and the oil boiler.
This piping gives you options for controls also. On off aquastat, or try a differential controller for a bit more control efficiency

I don’t think that mix valve is piped correctly, change that in the repipe. You need a circ on the H port of the mix valve. It pulls some hot and some return to blend accurately. Piping example below.

Kkane97

hot_rod said:

A WAG in the shop load 40,000 btu/ hr, calling it 25 btu/ sq ft. I don’t know what the house load is, but you should have plenty of boiler capacity. Too much boiler and they tend to shut down often, possibly smolder much of the season. Oxygen starved conditions tend to create more emissions and smoke. Any neighbors close by, downwind? At the very least consider my suggestion about primary secondary piping. It is this simple. Come off the HX with a short piece of 1-1/4 or 1-1/2” copper. That creates a hydraulic separation. Then tee in your existing circulators to those branches and the oil boiler. This piping gives you options for controls also. On off aquastat, or try a differential controller for a bit more control efficiency I don’t think that mix valve is piped correctly, change that in the repipe. You need a circ on the H port of the mix valve. It pulls some hot and some return to blend accurately. Piping example below.

We went over the mix valve in place in my other post with the staple up radiant, I am planning on changing it around during this modification. 

I don't follow the purpose of the copper off the HX

I went with a smaller boiler that should be able to manage the shop or house solely with a little extra I was figuring. 

What does WAG stand for?

hot_rod

The large pipe coming off the HX creates a hydraulic separation, primary secondary piping. This allows the multiple flow rates from the oil boiler and distribution circulators to all get along so to speak
Idronics 15 exp,sins the concept of hydraulic separation.

WAG wild a— guess

Kkane97

hot_rod said:

A WAG in the shop load 40,000 btu/ hr, calling it 25 btu/ sq ft. I don’t know what the house load is, but you should have plenty of boiler capacity. Too much boiler and they tend to shut down often, possibly smolder much of the season. Oxygen starved conditions tend to create more emissions and smoke. Any neighbors close by, downwind? At the very least consider my suggestion about primary secondary piping. It is this simple. Come off the HX with a short piece of 1-1/4 or 1-1/2” copper. That creates a hydraulic separation. Then tee in your existing circulators to those branches and the oil boiler. This piping gives you options for controls also. On off aquastat, or try a differential controller for a bit more control efficiency I don’t think that mix valve is piped correctly, change that in the repipe. You need a circ on the H port of the mix valve. It pulls some hot and some return to blend accurately. Piping example below.

In that example I would use the shop as the first zone off the OWB?


I don't know what that symbol is bottom right 

hot_rod

Your drawing showed 4 connections on the wood boiler. So you have two different independent systems

sounds like the boiler us large enough to handle both buildings at the same time?

do each building has its own piping Hx a
and controls

The pic if the manifold with pumos I assume is in the house? In a basement?