Indoor wood boiler tied into current oil/hydronic system?

[bryankloos]

Guys,

Is it possible to have an indoor wood boiler supply the heat (hydronic baseboard) while maintaining the oil burner as backup or for when traveling?

I have a good oil furnace but would love to know if it's possible to add wood heat to the equation.

Sorry if this is a basic question...

 

[maple1]

Yes. Better get reading.

Even better to yank the oil all together & replace with something else for backup - depending on your total situation.

 

[KevinD]

This is a feasible option. Especially if your mechanical apt and can do the install yourself. Ive been using a parallel oil hot water with solid fuel for over twenty years. Super cost efficient especially if your wood supply is free (labor excluded). Today I would consider a high efficient gasification boiler as the biggest maintenance and heat transfer issue I experienced with a wood boiler is cleaning the heat exchange surfaces of creosote. Good luck and enjoy the research plenty of in this forum to help you make a decision.

 

[bryankloos]

Seems like a parallel wood/oil system with pressurized storage would fit the bill.

I have spent some time reading here, and know a little about wood boilers. My theoretical questions were more about having both units work in the same system and how this is accomplished.

For my purposes, I would need a wood boiler, storage, and appropriate plumbing/controls to tie the two systems together. If you had to estimate, what is the cost of entry for the above given the homeowner does the install?

Thanks,

Bryan

 

[maple1]

You'd also need expansion tank(s) if doing pressurized storage - or else unpressurized with heat exchangers.

I ripped out a wood/oil combo boiler, and put in a new gassifying wood boiler, 660 gallons of storage, expansion tank, new 80 gallon electric hot water heater, and electric boiler for backup heat. Me doing everything (except wiring the boiler & heater), I was at around $15k. But that included almost $2k getting the boiler freighted to me with brokerage fees & an exchange rate hit. Also includes boxing in & insulating my tanks - but they're not what I'd call 'finished' even yet. The thing I underestimated the most was cost of fittings & piping. I just moved all my existing controls over to the new setup so likely saved some there.

Make sure you fully evaluate your oil/backup situation: how much you will be away in the winter, how much would the backup heat actually be used, what other fuel choices would you have for that (propane in the house? natural gas in your area?), what do you have for an oil boiler now & how old is it & the tank, and how do you heat your DHW? In my case, our DHW was with the oil boiler tankless coil, our oil tank was due for replacement in two years, and we are only away for 2 days in the winter over Christmas. So we sent the oil man packing. Our total electric bill since then maxes out at around $130/mo in summer when heating DHW electrically - otherwise around $100. Oil bills went to zero - along with potential future oil-related liabilities, like the kind that come with leaks.

 

[henfruit]

With boiler, 1000 gallons of storage and the parts to build the system. $13,000.00

 

[bryankloos]

The current system is a Viessmann Boiler with a Reillo burner, feeding a 5 zone (4 heat, 1 DHW) hydronic system with baseboard. I have 2x275gal tanks which are inside the basement. The buried tank was removed by the previous owner. The system is complete, working very well (87% efficiency) and is only 6 years old.

This is our first year in the house. I installed an insert to offset the oil use which has been great. I'm only burning 10-15% of what the previous owner burned last year. That said, the insert is not good at heating distant rooms (kids rooms) and the home has hot and cold spots. This is my reason for searching here.

I don't have NG available. I do have propane (3 tanks, 125gal each) which we use for the pool heater and a future generator.

We travel frequently on weekends in the winter hence my need for backup. As the oil boiler is in great shape we would like to preserve it for backup heat in the event we leave town for any appreciable amount of time in the winter, which we will do...

Henfruit... I'm jealous of your view. I moved from MA to CT last year to be closer to family. I was frequently up in your area hiking in the summer and skiing in the winter. It is tops on my list of areas for the wife and I to retire (in about 25 years).

 

[henfruit]

Henfruit... I'm jealous of your view. I moved from MA to CT last year to be closer to family. I was frequently up in your area hiking in the summer and skiing in the winter. It is tops on my list of areas for the wife and I to retire (in about 25 years).

I lived in Mass for 47 years on the ocean. From one extreme view to the other.

 

[bryankloos]

You can see the original view from the top of your new view...
Used to love hiking up to Tucks in the winter to camp and ski.
The wife thought I was crazy.

 

[maple1]

The current system is a Viessmann Boiler with a Reillo burner, feeding a 5 zone (4 heat, 1 DHW) hydronic system with baseboard. I have 2x275gal tanks which are inside the basement. The buried tank was removed by the previous owner. The system is complete, working very well (87% efficiency) and is only 6 years old.

This is our first year in the house. I installed an insert to offset the oil use which has been great. I'm only burning 10-15% of what the previous owner burned last year. That said, the insert is not good at heating distant rooms (kids rooms) and the home has hot and cold spots. This is my reason for searching here.

I don't have NG available. I do have propane (3 tanks, 125gal each) which we use for the pool heater and a future generator.

We travel frequently on weekends in the winter hence my need for backup. As the oil boiler is in great shape we would like to preserve it for backup heat in the event we leave town for any appreciable amount of time in the winter, which we will do...

Henfruit... I'm jealous of your view. I moved from MA to CT last year to be closer to family. I was frequently up in your area hiking in the summer and skiing in the winter. It is tops on my list of areas for the wife and I to retire (in about 25 years).

OK, sounds like your oil side is pretty solid. I would likely also leave it in place in that situation - might consider summer DHW with a heat pump water heater if you're running a tankless coil, but if you're doing cold start with an indirect would likely leave that too. I also might consider freeing up some space by getting rid of one of the tanks. Beyond that, lots of possibilities - and budget considerations. BTW, it's also possible (and likely easier and maybe cheaper) to add on a pellet boiler - depending on your wood & pellet situation there. It would do away with a need for storage tanks at least.

 

[bryankloos]

I can get wood for free/cheap which would be the desired fuel of choice. I have room for storage, especially if I remove one of the 275s so that's not an issue.

Is there a place to view plumbing schematics so that I can see how a parallel system is plumbed? I'm very handy and probably capable of installing the system myself, given I have resources should problems arise during install.

Here's a quick question. Can you share a single flue with the existing oil boiler or do each devices require their own? I have two flues in the external chimney with cleanouts in the basement. One is used for the boiler while the other is used for a fireplace insert on the first floor.

 

[leon]

The fossil fuel boiler cannot share the same
flue with a wood or coal fired boiler per plumbing codes

I have the same set up Bryan, The idea is to have the circulators
tied into the existing thermostat and a separate pump to balance the
temperature between the two boilers. The high limit on the boiler will
protect the boilers if the wood coal unit overheats by dumping the
excess heat into the home.

You will be better off with a power exhaust on the wood and coal boiler with a
metal chimney above the peak of the roof.

You will need an external air supply as well to provide enough combustion air too.

It would be simple enough to add a dryer vent in reverse with a screen on the outside wall
to keep any animals out of the basement.


You may want to seriously think about a small building for your wood / coal boiler as you will keep the mess away from the house UNLESS, You could have a wood chute made as opening doors and closing them thirty plus times a day makes life less than interesting (speaking as a wood and coal burner for 32 years.

I would have had the the bloody thing put in single car garage and been done with it 32 years ago if I could have afforded it

Its better to start fresh and build a small insulated shed with fire resistant sheet rock and simply use the $15 per foot insulated PEX and leave the pumps inside to avoid freezing


You will have to do a considerable amount of work to provide the proper clearances in a basement installation.

The other issue is excess dryness in the basement ashes and the occasional smurf with a flame thrower shooting three foot fsolid blue flames out the ash pit air draft.

flying embers and and the smurf with a flame thrower are major concerns in a very dry home.

The use of an exterior building can also give you lots of room for water storage and if you can find a surplus bulk milk tank you will save a bundle of money.

 

[maple1]

Leon - coal is not on everyones list of possibilities, so why keep bringing it up. If you're burning wood, get a wood burner.

I had oil & wood into the same flue for 17 years. So check your local codes on that. You may be able to powervent your oil & vent your wood into the flue where your oil is now. I don't think I've read of anyone 'power exhausting' their wood boiler - what does that mean?

I also would have my setup nowhere but in my basement. Opening doors 30 times a day? What? I didn't have to install any new air intakes, and I certainly have no episodes that Leon speaks of and seems afraid of, and am not worried I ever will. But I certainly won't try to tell someone who is installing in an outbuilding that they're doing it wrong, as Leon seems to be saying about a basement install.

Just make like a sponge on here, and read everything you can find. It's all here (except for localized issues like wood supply & building codes). Assess all the choices & possibilities, and weigh all your priorities & preferences. Easy to say, right?

 

[flyingcow]

bryankloos- I did what you want to do about 6 yrs ago. Left my oil set up in place. When my storage gets down to a point I determine, oil system automatically takes over. Or i can throw a switch and the oil takes over. Works pretty good.

 

[bryankloos]

Ok. The way I see it the oil boiler jests the storage water which is then used to circulate through the baseboard and DHW tank when the zones call for heat. The boiler maintains storage temp and if the wood boiler goes out or the storage cools below a set point the oil furnace kicks in to heat the water fed to the zones.


How is each boiler isolated when not needed. That is when firing the wood boiler how does the circulation void traveling through the oil boiler?

Also how is the storage isolated when the wood boiler is running, as the heat should be shunted directly to the rads and not storage...?

I guess some flow diagrams would help here relative to tieing the two systems together in parallel.

 

[flyingcow]

My unit was installed per Tarm's diagrams. Right now I have a fire going.T-stats are calling for heat, a thermo valve is opening and sending heat(from the boiler) to my zones and whatever heat from the boiler isn't used it sends to storage. When T-stats are satisifed, the thermo valve puts all the energy into storage thru a HX in my tank. When boiler is out, the same HX pulls heat back out and sends to house. I am sure i just confused you, someone else can explain better.

Basically a zone valve will keep the flow thru the oil boiler when not in use. You need to look at Tarm's diagrams, thats what i have.

I'll see if i can find it. There are various ways to do this.

 

[henfruit]

My system is wood boiler to tank, tank to house system. When wood boiler is running and house is calling for heat, some of the hot water goes to the house and some to the tank. The pump in the house that circulates the water through the tank to the house system is controlled by a two stage ranco aquastat. The oil boiler is also powered through this aquastat. When the tank temp is above 140 degrees the oil can not run. When the temperature drops below 140 the aquastat flips power to the oil side and shuts off power to the circulator. I use pumps with flow checks so I do not back feed the storage tank.

 

[bryankloos]

While most likely under my nose, would anyone have a link to these diagrams.
This is fascinating research... My engineering mind is racing!

 

[peakbagger]

My system is set up with wood as primary and oil as backup. If the storage tank is above 140 degrees, then the oil burner is locked out. All the circulators are run by the oil boiler but instead of the oil burner running, it routes the hot water through the storage tank coil. I did it all in relay logic and if the power is turned off, the wood boiler all the relays and controls reset to a normal oil system. A PLC would be far more elegant and have some more capabilities but relays work for me.

 

[Rory]

I have a simple setup in which the oil boiler monitors the storage tank via a setpoint controller. It works, but my furnace seems to run pretty short cycles; my cousin has a heating background and suggested I might be able to up my furnace limit, but I haven't tried it. I'm surprised hiker88 hasn't weighed in yet, he was just telling me he has a controller from Tarm that can be set 3 different ways for wood, oil or both, and his oil furnace has a built in water coil, so it doesn't circulate to the tank.

 

[hiker88]

Go to woodboilers.com, select any of the three wood boilers on the left, then Scroll down and there are some tabs. Select documentation, and then download the plumbing schematics diagram.

Flying cow and I have slightly different boilers, but I think we both have set ups as provided by Tarm. My project was a DIY, so I wanted to be able to call Tarm for tech support and start off from a known constant.

I have unpressurized storage, or what Tarm calls the "square tank setup". Rory is correct, I have the Tarm "BLT" controller which will run in wood only, auto backup, or backup only modes The field wiring for the blt is in the schematics Tarm provides, if you are interested.

In wood only, the oil furnace ca't fire if it is a cold start boiler, if it is a tankless coil oil furnace like I have, you need to make a mod which Tarm helped me do over the phone. The blt controller is connected to your oil furnace tt terminals, and in wood only, they are always open.

When my wood boiler is going, heat is supplied directly to rads when there is a call for heat, storage is locked out. When demand is met, zone valves close, all but the boiler circ pump shut off, and all supply is routed to storage. I like it when the boiler is really rolling and there is a call for heat-I hear the thermostat click, and about 10 seconds later I can feel that 195f water hit the baseboard.

In auto backup, an open on rise aquastat monitors storage. When storage temp drops below my set point, the aqua stat closes and shorts the tt terminals on the oil furnace and allow it to start. My system with the oil furnace running works exactly the same as it did before I installed the wood furnace. The oil furnace does not heat storage, when there is a call for heat, heat goes directly to rads, and the oil burner aqua stat determines if the boiler needs to fire or not based on high/ low limits and differential.

Auto back up is interesting because you can have the oil furnace, and wood boiler going at the same time. If we get home late on one of these cold nights, I will put the controller in auto backup. The oil furnace will come on, and I have quick heat. I start a fire in the Froling, and when it gets to 149f, it will launch the circ pump and start heating storage. Once storage meets set point, the open on rise AQ opens, the oil furnace shuts off, and then depending on if there is demand, the wood boiler will either heat the house, or storage.

I have no clue what backup only mode is for, I've never used it. JK, but you can figure that out.

With my heat load and the amount of storage I have, the blt is almost always in wood only. Even with this weather lately, if I completely charge my storage at night, I can come home from work the next day and the house is at worst 66 or 67.

Let us know if you have any more questions. There are some very knowledgeable and friendly people on this forum.

 

[flyingcow]

Reading that hiker88, sounds like you've seen my set up.

I had the installer follow Tarms diagrams. Used Tarms parts, etc. For the same reason as hiker, if i have problems you can diagnose over the phone and there shouldn't be any second guessing. My installer is hours away. Had a minor problem and it was easy to figure out.


Bryankloos---,for me whether it was Tarm , AHONA, GARN, or whoever I would have had it installed per their diagrams. I'm not very adventurous with stuff like that. Not my level of comfort. Plus if there is problems, it's their problem, or at least you hope.

But anytime you want to go for a 500 mile ride in a milk truck, when a nor' easter is barreling up the coast, thats my comfort zone.

 

[velvetfoot]

Can I ask a quick question on how you guys charge your unpressurized storage tanks? Is there a coil involved? And does the storage water circulate through the baseboards (or whatever)? I'll take a look at those sites in your sigs. Thanks.

 

[maple1]

Can I ask a quick question on how you guys charge your unpressurized storage tanks? Is there a coil involved? And does the storage water circulate through the baseboards (or whatever)? I'll take a look at those sites in your sigs. Thanks.

Usually a coil for heat going in, and another for heat going out. Tank water stays in the tank.

 

[henfruit]

Just one coil. You tee off of the inlet and return to feed and return from the house system.