Plumbing an oil boiler and wood boiler stove - HELP PLEASE!

[smartcarfun]

So I bought a wood burning stove with a back boiler on it.
Gosh I thought that was a great idea... just pull out the old fireplace and bingo... a few pipes later and amazing heat throughout the house...

Well it hasn't quite worked out that way, when I looked online and saw the complexity I decided on a plumber but plumbers around where I live aren't too keen on trying to match these into existing systems, they like the new builds but not the rebuilds.

So I have pulled my plumbing apart, I've pulled the fireplace apart and its February and I have no heat.....!

Hoping you guys can help me out here... Ive taken what I have found on the net and come up with this schematic.

1" copper from the oil boiler to a junction of T's, Non Return Valve on the flow and pump on the return.
1" copper from the wood boiler jioning the T's on the opposite side to the oil with Non Return Valve on the flow and pump on the return. On the boiler side before the Non Return Valve on the flow and the pump on the return, 2 x T's take a gravity flow to the dual coil cylinder and expansion tank.
After the flow and return junctions of T's are 2 x motorised valves for ground and 1st floor radiators.
The flow and return to the dual coil cylinder is allways open.
Piping after the junction of T's is a mix of 3/4" copper and qual-pex.
Relays and switchs will mean only one system works at anyone time, ie when the wood boiler heats sufficently it kills the oil boiler and when it cools the oil boiler kicks in.

My question is will this work and have I missed anything? Injector T's where mentioned to me but I don't know if I need them?
Also a presure release valve, where should I put one?

Thanks for reading...

SCF

 

[joecool85]

Looks to me like it could work that way. Might make it easier if you just plumb it in series, leave all the rest of it alone.

The hot water out of the wood boiler would go to the return on the oil boiler, and the cold water return on the wood boiler would go to the hot supply on the oil boiler. Run a pump in that loop. Then any time the wood boiler is putting out heat, the oil kicks off. Any time the wood stops putting out heat, the oil kicks on.

Simple.

 

[stee6043]

Looks to me like it could work that way. Might make it easier if you just plumb it in series, leave all the rest of it alone.

The hot water out of the wood boiler would go to the return on the oil boiler, and the cold water return on the wood boiler would go to the hot supply on the oil boiler. Run a pump in that loop. Then any time the wood boiler is putting out heat, the oil kicks off. Any time the wood stops putting out heat, the oil kicks on.

Simple.

+1. I'd run exactly in this way as well. In doing so you really only need two (2) new connections to your existing system. One for supply and one for return. Vastly simplifies installation I would think. And you also have a built in fail safe as mentioned above. If your wood boiler is not heating the water, your oil boiler will.

 

[WoodNotOil]

Looks to me like it could work that way. Might make it easier if you just plumb it in series, leave all the rest of it alone.

The hot water out of the wood boiler would go to the return on the oil boiler, and the cold water return on the wood boiler would go to the hot supply on the oil boiler. Run a pump in that loop. Then any time the wood boiler is putting out heat, the oil kicks off. Any time the wood stops putting out heat, the oil kicks on.

Simple.

+1. I'd run exactly in this way as well. In doing so you really only need two (2) new connections to your existing system. One for supply and one for return. Vastly simplifies installation I would think. And you also have a built in fail safe as mentioned above. If your wood boiler is not heating the water, your oil boiler will.

The problem with a series hookup though is that the heated water from the wood stove will mix with returning zone water and lower the usuable temp, making the oil run even when the wood is good and hot.

I think your diagram would work. You will need to figure out how to stop the oil from staying hot when the wood is hot. I also don't understand what pumps water through the hot water tank from the wood system. There is no pump in that line. There is likely a pressure relief valve on your oil boiler. You can also put one on your wood unit similar to how it is plumbed on the oil one (same pressure rating and everything) just to be on the safe side.

 

[smartcarfun]

The problem with a series hookup though is that the heated water from the wood stove will mix with returning zone water and lower the usuable temp, making the oil run even when the wood is good and hot.

I think your diagram would work. You will need to figure out how to stop the oil from staying hot when the wood is hot. I also don't understand what pumps water through the hot water tank from the wood system. There is no pump in that line. There is likely a pressure relief valve on your oil boiler. You can also put one on your wood unit similar to how it is plumbed on the oil one (same pressure rating and everything) just to be on the safe side.

Joecool and stee
Thanks for your ideas, I take WoodNotOil's point about the cooler water mix, also there is the point that the wiring is such that if the oil boiler turns off so does the pump unless its forced on an in the case of going to bed and putting that last log in the fire to keep some hot water in the system, the oil boiler will kick in through the night. In my world oil is expensive so it tends to be kept for the waking hours.

WoodNotOil
Attached is the wiring diagram which in a nutshell "if Im correct!" when the pipe stat senses heat from the wood fire, it will interrupt the power from the main timer/advance oil boiler controler, sending instead power to a simple rotary switch which selects which zones to open at anytime... Im hoping this is simple enough to install and works in a stupid proof manner, comments appreciated....

About your question regarding the the wood flow to the hot water tank, its a gravity feed Im told you need in case of a power cut. It is not directly above but above and slightly horizontal by about 2-3 meters which Im a little concerned about????? Is this what you guys think is the way to go?

Question about the return to the wood boiler???? The gravity return to the wood boiler is meant to be unrestricted so it is between the pump and the boiler.... will this mean in operation that the pump may force return from the zones up the gravity return and basicly try to reverse/block the gravity system?????? any ideas what the work around is????

Cheers again, this is all very helpful, back to plumbing tonight....!

SCF

 

[WoodNotOil]

The problem with a series hookup though is that the heated water from the wood stove will mix with returning zone water and lower the usuable temp, making the oil run even when the wood is good and hot.

I think your diagram would work. You will need to figure out how to stop the oil from staying hot when the wood is hot. I also don't understand what pumps water through the hot water tank from the wood system. There is no pump in that line. There is likely a pressure relief valve on your oil boiler. You can also put one on your wood unit similar to how it is plumbed on the oil one (same pressure rating and everything) just to be on the safe side.

Joecool and stee
Thanks for your ideas, I take WoodNotOil's point about the cooler water mix, also there is the point that the wiring is such that if the oil boiler turns off so does the pump unless its forced on an in the case of going to bed and putting that last log in the fire to keep some hot water in the system, the oil boiler will kick in through the night. In my world oil is expensive so it tends to be kept for the waking hours.

WoodNotOil
Attached is the wiring diagram which in a nutshell "if Im correct!" when the pipe stat senses heat from the wood fire, it will interrupt the power from the main timer/advance oil boiler controler, sending instead power to a simple rotary switch which selects which zones to open at anytime... Im hoping this is simple enough to install and works in a stupid proof manner, comments appreciated....

About your question regarding the the wood flow to the hot water tank, its a gravity feed Im told you need in case of a power cut. It is not directly above but above and slightly horizontal by about 2-3 meters which Im a little concerned about????? Is this what you guys think is the way to go?

Question about the return to the wood boiler???? The gravity return to the wood boiler is meant to be unrestricted so it is between the pump and the boiler.... will this mean in operation that the pump may force return from the zones up the gravity return and basicly try to reverse/block the gravity system?????? any ideas what the work around is????

Cheers again, this is all very helpful, back to plumbing tonight....!

SCF

The gravity line should be fine, but you may want to put a check valve in it to insure it only flows in the desired direction. I am not sure if that would restrict the flow at all though?

The controls look good in theory. I am assuming you have everything rated for the correct voltage and amps etc. I think you are definitely on the right track here.

 

[Tony H]

I think your diagram would work. You will need to figure out how to stop the oil from staying hot when the wood is hot. I also don't understand what pumps water through the hot water tank from the wood system. There is no pump in that line. There is likely a pressure relief valve on your oil boiler. You can also put one on your wood unit similar to how it is plumbed on the oil one (same pressure rating and everything) just to be on the safe side.

Joecool and stee
Thanks for your ideas, I take WoodNotOil's point about the cooler water mix, also there is the point that the wiring is such that if the oil boiler turns off so does the pump unless its forced on an in the case of going to bed and putting that last log in the fire to keep some hot water in the system, the oil boiler will kick in through the night. In my world oil is expensive so it tends to be kept for the waking hours.


SCF

Can you run the simple setup and just adjust the thermo on the oil so the temp has to drop quite low before it kicks in.
Most if not all of my family in Ireland shut down the boiler or turn the temp way down low when they go to bed.

 

[smartcarfun]

Can you run the simple setup and just adjust the thermo on the oil so the temp has to drop quite low before it kicks in.
Most if not all of my family in Ireland shut down the boiler or turn the temp way down low when they go to bed.

I kind of dismissed this idea but maybe I should think a bit more about it, it sounds simple. i guess I still need a gravity line to an expansion tank and dual coil cylinder in case of a power cut?

Do you have a diagram of how it might work and where you branch out to the zones?

Cheers

SCF

 

[Gooserider]

My preference is for a parallel hookup so that you aren't sending heat to the unused burner, which is generally a more efficient way to do things, and is sort of what SCF is doing with his original post. I'm not sure about the gravity loop to the DHW heater, other than as an emergency power failure / overheat heat dump, controlled by an automag or equivalent... I'm also unclear on why he needs two expansion tanks. Lastly what is that "Radiator Heat Leak" over on the left above the wood unit?

My approach would mostly be simplification....

I would put a flow check on each of the two pumps so that you can't get reverse flow through which ever one is not running.

I would get rid of the extra expansion tank, and possibly that gravity loop to the DHW tank, replacing it with some other sort of emergency dump loop, like a run of baseboard on the ceiling or some such... If i did keep the gravity loop to the tank, I'd design it the same way I did any other emergency loop, with an automag valve hooked up to an aquastat on the wood boiler.

I would also put a pressure relief valve on the wood boiler that matched the one on the oil boiler, just as a safety measure.

Also on the subject of safety, if you don't have a "tempering" or "mix-down" valve on the output side of the DHW tank already, you probably will want to add one in order to avoid any scalding risk.

One side note that does somewhat concern me - at least here in the US, inserts and stoves are mostly designed as local area space heaters, and don't have any sort of water heating ability. The very few units that do have water heating ability, as well as most aftermarket and home built units don't have a lot of heating capacity, and often have a hard time making enough hot water just for DHW use - do you have any specs that can verify that this unit will actually put out enough heating power (KW or BTU/hr) to carry the entire house load?

Gooserider

 

[smartcarfun]

Gooserider,
Thanks very much for your input. I had to do some research into your comments as I was a little unfamiliar with your terms and some of the products you guys have. So this is what I now recon is the best way to go....

"the gravity loop to the DHW heater, other than as an emergency power failure / overheat heat dump, controlled by an automag or equivalent... "

The gravity loop is only in the case of power failure and supplies an escape for heat through the hot water tank to an expansion tank. This loop is constantly open so should not need an automag (motorised valve/open when off) however I will monitor the flow and if I’m losing too much heat up the gravity loop when in operation I may but an automag in place to keep the flow in the direction I desire, is this correct?

“... I'm also unclear on why he needs two expansion tanks”

I will use a single expansion tank but run the loop to it as opposed to cutting in to the current flow and return as it is in ¾ inch copper and my gravity loop is in 1 inch copper.

“Lastly what is that "Radiator Heat Leak" over on the left above the wood unit?”

There is one small radiator also attached to this gravity loop which will act to dissipate the heat if there is now power. It should also naturally give off heat when the system is working correctly. However if I put an automag on the gravity loop flow this would starve this radiator of heat in normal operation.

“My approach would mostly be simplification....
I would put a flow check on each of the two pumps so that you can't get reverse flow through which ever one is not running.”

Done, a flow check is a Non Return Valve (NRV) and I have two, one on each flow and in the case of the wood stove it is after the gravity loop to minimise obstruction.

“I would get rid of the extra expansion tank, and possibly that gravity loop to the DHW tank, replacing it with some other sort of emergency dump loop, like a run of baseboard on the ceiling or some such...”

Here is where I could not understand what you were referring to “a run of baseboard on the ceiling” I’m not familiar with baseboard or a product that could act as a heat dump in the attic, could you enlighten me a bit more on this area...

“I would also put a pressure relief valve on the wood boiler that matched the one on the oil boiler, just as a safety measure.”

Done, will add this as a precaution.

“Also on the subject of safety, if you don't have a "tempering" or "mix-down" valve on the output side of the DHW tank already, you probably will want to add one in order to avoid any scalding risk.”

I had a look at this and don’t think I need this as the tank I am using is indirect as opposed to direct thus the water should not reach scolding????

“One side note that does somewhat concern me - at least here in the US, inserts and stoves are mostly designed as local area space heaters, and don't have any sort of water heating ability. The very few units that do have water heating ability, as well as most aftermarket and home built units don't have a lot of heating capacity, and often have a hard time making enough hot water just for DHW use - do you have any specs that can verify that this unit will actually put out enough heating power (KW or BTU/hr) to carry the entire house load?”

The rating for this stove is 14KW to water and 6KW to room, thus the reason I need it to go through my motorised valves as I believe it will be sufficient to heat only one area at a time... Very similar too http://www.mulberrystoves.com/products-beckett.html


I have been told to put an injector tee on the return to the stove where the return from the system meets the return from the gravity loop so I am not pushing pumped return water back up the gravity return????

Thanks very much to all, this info has been of great help. Hope to start this in a week so if anyone has any comments please post, otherwise I will return with good or bad news

SCF

 

[Gooserider]

Gooserider,
Thanks very much for your input. I had to do some research into your comments as I was a little unfamiliar with your terms and some of the products you guys have. So this is what I now recon is the best way to go....

No problem, we aren't always familiar with what you have on your side of the pond either... :lol:

"the gravity loop to the DHW heater, other than as an emergency power failure / overheat heat dump, controlled by an automag or equivalent... "

The gravity loop is only in the case of power failure and supplies an escape for heat through the hot water tank to an expansion tank. This loop is constantly open so should not need an automag (motorised valve/open when off) however I will monitor the flow and if I’m losing too much heat up the gravity loop when in operation I may but an automag in place to keep the flow in the direction I desire, is this correct?

If you aren't losing a lot of heat up that loop, I'd be concerned that your gravity flow wasn't setup right for it to work in a power failure. (I strongly advise folks to test their system by turning off the power on a full burn fire, and make sure that nothing overheats while watching it, and being ready to turn power on if needed.) I would consider the automag valve to be pretty much of an absolute requirement, or you will lose a lot of heat in that loop. The automag would also solve your concern about backflow through the gravity loop when the pumps are running.

“... I'm also unclear on why he needs two expansion tanks”

I will use a single expansion tank but run the loop to it as opposed to cutting in to the current flow and return as it is in ¾ inch copper and my gravity loop is in 1 inch copper

. OK, but you shouldn't need an expansion tank on the gravity loop, as it would still be connected to the rest of the system, and you only need one point of expansion as long as it's properly sized (there are formulas for this), and you will probably need to make the existing tank larger to make up for the increased system volume from the new stove and plumbing. http://www.b2epc.com/software/tank.shtml is one site that will help you figure the size needed - sorry but it seems to be English units only.

“Lastly what is that "Radiator Heat Leak" over on the left above the wood unit?”

There is one small radiator also attached to this gravity loop which will act to dissipate the heat if there is now power. It should also naturally give off heat when the system is working correctly. However if I put an automag on the gravity loop flow this would starve this radiator of heat in normal operation.

True, but unless that radiator is needed for normal heat, why is it there? Can it be moved to a zone that gets heat from normal flow, not the emergency dump zone?

“My approach would mostly be simplification.... I would put a flow check on each of the two pumps so that you can't get reverse flow through which ever one is not running.”

Done, a flow check is a Non Return Valve (NRV) and I have two, one on each flow and in the case of the wood stove it is after the gravity loop to minimise obstruction.

- Agreed. Note that here in the US, we can get pumps with the NRV's built into the pump body, which is supposed to be more efficient, however there is nothing wrong w/ separate units.

“I would get rid of the extra expansion tank, and possibly that gravity loop to the DHW tank, replacing it with some other sort of emergency dump loop, like a run of baseboard on the ceiling or some such...”

Here is where I could not understand what you were referring to “a run of baseboard on the ceiling” I’m not familiar with baseboard or a product that could act as a heat dump in the attic, could you enlighten me a bit more on this area...

What we call baseboard in the US is a radiation system that consists of a pipe running around the outside walls of a house at the corner of the floor and wall, replacing the wooden molding - the most common versions are copper tubes with fins on them, enclosed in a metal housing. This site http://www.slantfin.com/product-baseboard.html shows one of the more common brands. A very common dump zone tactic, especially in a dedicated boiler room, is to run a length of baseboard (often purchased used at the junkyard, and with the pretty cover removed) around the ceiling of the boiler room, and control it with an automag. As long as it won't get cold enough to freeze, it could be in an attic just as easily, as long as you do the right gravity flow piping design. You wouldn't need all that much - the rule of thumb that we have is approximately 10% of boiler capacity, at 500BTU / foot for 3/4" baseboard. Your unit sounds like about 47.8kBTU capacity, call it 50,000BTU so 10% would be 5,000BTU or 10 feet. We have also seen people use cast iron radiators for dump zones. Pretty much anything will do as long as it gets rid of the heat.

“I would also put a pressure relief valve on the wood boiler that matched the one on the oil boiler, just as a safety measure.”

Done, will add this as a precaution.

Good... It may be overly cautious of me, but I like to see a pressure relief valve on any heat making part of a system. It shouldn't happen, but if the unit does get isolated by shutoff valves, it can prevent a disaster. It is also pretty much required by building codes here in the US. (I'm not sure what your code and inspection requirements are)

Continuing in next message...

Gooserider

 

[Gooserider]

“Also on the subject of safety, if you don't have a "tempering" or "mix-down" valve on the output side of the DHW tank already, you probably will want to add one in order to avoid any scalding risk.”

I had a look at this and don’t think I need this as the tank I am using is indirect as opposed to direct thus the water should not reach scolding????

Looking at the diagram, it appears to me that you will have water going through the indirect water heater tank any time the fossil or wood boiler pump is running - looks like you have a connection on the right side of both manifolds and I don't see any flow control valve. Given time, an indirect can definitely heat the water in a storage tank to within a degree or two of the water temp coming out of the boiler, which you MUST assume could get up close to boiling at times - Thus it is quite reasonable to expect that you might see the DHW tank reach well over 120°F (49°C) which is the maximum temperature that US codes allow at a hot water faucet (note that hotter than that can cause severe burns in seconds!) You don't have the same issue with a fossil boiler because the output of the boiler is much more controlled, and you have thermostats that will shut it off on demand, which you can't do with a wood fire.

I would say that it's a definite safety concern, and would want you to either have a mixing valve on the tank output, or a zone valve (what you are calling a motorized valve) on the water heater line to keep it from getting over heated.

Many of our users that have mixing valves actually heat their hot water tanks up as hot as they can, because this gives them the effect of having a bigger supply of hot water since they have to mix it back down with cold in order to get the right temperature.

“One side note that does somewhat concern me - at least here in the US, inserts and stoves are mostly designed as local area space heaters, and don't have any sort of water heating ability. The very few units that do have water heating ability, as well as most aftermarket and home built units don't have a lot of heating capacity, and often have a hard time making enough hot water just for DHW use - do you have any specs that can verify that this unit will actually put out enough heating power (KW or BTU/hr) to carry the entire house load?”

The rating for this stove is 14KW to water and 6KW to room, thus the reason I need it to go through my motorised valves as I believe it will be sufficient to heat only one area at a time... Very similar too http://www.mulberrystoves.com/products-beckett.html

OK, as I mentioned earlier, my favorite unit conversion site said 14 KW is a little less than 50,000 BTU/hr, which is on the small side by US standards, but it does sound like it should do the job. We don't seem to have any US equivalents to the unit you linked to, which is to bad in some ways, as they look like nice units, and we don't really have anything that matches the description of a boiler that is suitable to put in a living space. We have a lot of gasification boilers (many of them EU imports) but they are all the type of unit one would put in a dedicated boiler room, not as the centerpiece of your living area...

I have been told to put an injector tee on the return to the stove where the return from the system meets the return from the gravity loop so I am not pushing pumped return water back up the gravity return????

As drawn, that wouldn't be a bad idea, to possibly prevent back feeding (I'm not sure it would work), but it would make the problem of non-emergency flow through the dump loop even worse as it would pull water through it... If you did the automag, it wouldn't be needed.

Thanks very much to all, this info has been of great help. Hope to start this in a week so if anyone has any comments please post, otherwise I will return with good or bad news

SCF

Glad to help out - keep us posted on your progress, and remember that we love pictures... :cheese:

Gooserider