Need advice on SIMPLE wood boiler integration

[lukem]

I'm very seriously considering a wood fired boiler before next winter. Boiler make/model is TBD.

Right now I'm trying to conceptualize how I can easily integrate it with my current propane fired radiant heat system. The current boiler has iron pipe. It is either 1.25 or 1.5" pipe into and out of the boiler. Single zone with one circ pump. I have circa 1960 radiant panels throughout. The house has received numerous insulation improvements over the years so I probably have way more baseboard than is currently required.

Could it be as simple as adding a plate exchanger to the cold side of the propane boiler? And somehow control the existing pump with another thermostat?

 

[b33p3r]

Lukem, Depends on your needs mostly. My wood boiler circulates directly through my oil boiler. Just teed off the black pipe before and after oil boiler. As long as the wood boiler is pumping hot water through the oil boiler the oil boiler never fires. I don't run glycol in my system and both boilers are pressurized so I didn't need a heat exchanger. Your current thermostat/circ pump setup will still be active as long as you don't turn the propane boiler off.
My setup is a very basic one. Stick around. There are alot of very intelligent people in here that can give you more efficient options than my simple setup.

 

[Nofossil]

I did the 'simplest pressurized storage' sticky a few years back for situations like yours. Ignore the storage and drop the load circulator. You'll need a circ for each heat source, and zone valves if you have more than one zone. You can use a snap switch on the wood boiler outlet to disable the demand signal to the propane boiler.

 

[peakbagger]

I ran my wood boiler for several years with it just circulating through the exisitng oil boiler and using the original controls with a lockout relay on the oil gun. It worked but was real inefficient in shoulder seasons. Basically the wood boiler is on/off and it takes hours to cycle so what would happen is everthing would be up to temp and then the wood boiler would shut its damper which lead to inefficent combustion and lots of smoke. I switched to running a wood stove for the shoulder seasons and then when it got real cold, I would run the wood boiler. With storage, I run the wood boiler once a day and then run off storage. Its a lot more efficient as the boiler rarely closes its damper due to lack of demand.

 

[lukem]

Thoughts on this?

Basically I would have a continuous, always-on loop running from the wood-fired heat-source (boiler and/or storage) through a plate exchanger for DHW and my current baseboard heat zone. I would circulate the baseboard heat zone using the existing circulation pump. Still don't know if I could make the same pump run from two different thermostats?

I would also have some valving in there for various bypasses and shut-offs for the plate exchangers (not shown)...just trying to see if this concept is feasible before getting too detailed.

Thanks for any input.

 

[b33p3r]

Lukem, The existing thermostat/circ pump would not be affected as long as you keep the propane boiler powered on. The aquastat in the propane boiler would be satisfied by the wood boiler loop. But the WB(wood boiler) will need to get heat "through" the PB(propane boiler). If a heat exchanger is necessary then you must add a circulator to move water through PB or add controls so circulator can be controlled by WB.
My setup left all control to the Oil Boiler(OB) aquastat. I did add a relay controlled by my WB that will not allow the OB to fire if the WB is up to temp. I also have another relay which allows the WB to turn the circulator on should their be an over temp situation in the WB.
Again, my system was set up with $$$m in mind. There are much better ways to do this. NoFossil as well as others on this forum are invaluable resources. I'll bow out at this point because I know you are in much better hands.

 

[Clarkbug]

You could tie into the supply pipe leaving your propane boiler with a set of closely spaced Tees (or a Taco Twin Tee) and use that for the supply/return from the wood boiler/storage. Nice and easy. Interrupt the signal to the propane gun with an aquastat placed on the supply line from the WB or in the top of the storage tank. When it gets cold, have it fire up the propane and kick off the wood boiler circ.

Just another option to think about as you plan.... Good luck!

 

[lukem]

Sounds like I'm being steered away from the design i posted, and that's fine, but would like to understand the downsides to what i have posted and why it should be changed. Not that i dont trust you...just want to learn. Great advice...keep it coming.

 

[maineDIY]

Sounds like I'm being steered away from the design i posted, and that's fine, but would like to understand the downsides to what i have posted and why it should be changed. Not that i dont trust you...just want to learn. Great advice...keep it coming.

I first started my wood boiler last season hooked up to my existing oil fired boiler in series. It reportedly is better for the oil boiler to remain hot. What I don't like about a "series" hookup is that the oil boiler is actually a pretty efficient radiator and sends heat going thru it up the chimney. I spent some time this summer re-plumbing the wood boiler to be in "parallel" to the oil boiler. I think it is already showing signs of increased efficiency--ie. less wood use---- although the real cold days are yet to come this season. The oil boiler needs replacement anyways so if this strategy ruins it (by letting it be cold) then it really won't be much lost.

GG

 

[lukem]

I first started my wood boiler last season hooked up to my existing oil fired boiler in series. It reportedly is better for the oil boiler to remain hot. What I don't like about a "series" hookup is that the oil boiler is actually a pretty efficient radiator and sends heat going thru it up the chimney. I spent some time this summer re-plumbing the wood boiler to be in "parallel" to the oil boiler. I think it is already showing signs of increased efficiency--ie. less wood use---- although the real cold days are yet to come this season. The oil boiler needs replacement anyways so if this strategy ruins it (by letting it be cold) then it really won't be much lost.

GG

I have considered the "radiator" effect and heat loss up the flue, but I figure I'm going to loose a lot of that heat with my current flue setup anyway (it is a "hood" type flue connection). Point taken, but wood consumption isn't a huge concern for me right now. Like you, I need to replace the propane boiler someday, so I want to keep it pretty simple and I can re-pipe later, if needed, when if/when I replace the PB.

 

[Gasifier]

I had my install guys pipe my WB in parallel to my OB. I use an indirect hot water heater to heat all my DHW. I believe these indirects are the best way to go, along with a pressurized system. But that is just my opinion. Mine is a triangle tube smart series. The indirect is insulated fairly well and provides endless hot water. And there is not much that can go wrong with them. They are kinda pricey though. You would have no need for a heat exchanger. Are you planning on putting storage in?

Weather or not you put storage in now or later, or go with an indirect hot water heater, you can pipe your new boiler in parallel to your existing boiler just as easy as you can in series. And your system will be better. Your gassification WB system will make you happy. Take your time and plan. Get your wood for next year now. Split it a little smaller than you would for a wood stove. This will keep gassification better by creating a good coal bed. Whatever boiler you choose will want nice dry wood. Keep the questions coming to these folks.

 

[lukem]

I had my install guys pipe my WB in parallel to my OB. I use an indirect hot water heater to heat all my DHW. I believe these indirects are the best way to go, along with a pressurized system. But that is just my opinion. Mine is a triangle tube smart series. The indirect is insulated fairly well and provides endless hot water. And there is not much that can go wrong with them. They are kinda pricey though. You would have no need for a heat exchanger. Are you planning on putting storage in?

Weather or not you put storage in now or later, or go with an indirect hot water heater, you can pipe your new boiler in parallel to your existing boiler just as easy as you can in series. And your system will be better. Your gassification WB system will make you happy. Take your time and plan. Get your wood for next year now. Split it a little smaller than you would for a wood stove. This will keep gassification better by creating a good coal bed. Whatever boiler you choose will want nice dry wood. Keep the questions coming to these folks.

I have 20 cord of wood c/s/s...some is now 3 years old. All set there.

Anyone have a drawing of a parallel installation...I can't picture it in my mind.

What is an indirect heater?

 

[Gasifier]

I have 20 cord of wood c/s/s...some is now 3 years old. All set there.

Anyone have a drawing of a parallel installation...I can't picture it in my mind.

What is an indirect heater?

This is a triangletube indirect heater. It is basically a thin walled tank inside of another tank. The hot water from your boiler system goes into the exterior tank and heats the interior tank. So your boiler water never mixes with your potable water. The interior tank is thin wall S.S. Works fantastic. Expensive, but worth it. I have had mine for about 8 years now and have had no issues. Like I said, there is not much that can go wrong with them. It was suggested to me because I live in the country where there is more of a chance of plugging up a heater that has a coil in them. Same as with a heat exchanger I would think. Although I do not know what the i.d. of the heat exchanger material is. ?

(broken link removed to http://www.triangletube.com/TriangleTubeProduct.aspx?CatID=6&PID=2)

Basically we installed a long primary loop. When the primary loop goes "by" your OB you simply install a "T" there and then when it begins it's return you install a "T" at the appropriate place to allow return water to go back to the bottom of your oil boiler. So when your oil boiler is running it is sending energy through your existing lines to your zones and returning it to the bottom of your oil boiler. When your WB is running it is sending energy past your oil boiler and to the same existing lines and zones and returning it to the bottom of your WB.

 

[Gasifier]

Lukem. I do not know if you know this already. But when you click on the boiler room, up at the top above the threads are several permanent threads or "stickies". Take a look at the last one by nofossil. Here is a picture of a parallel system from his.

 

[Gasifier]

As you can see his system uses on circ pump for each boiler, and then uses zone valves for each zone. I used a circ pump for each boiler and a circ pump for each zone, including a pump for the indirect heater which is like a zone itself. Works great.

 

[lukem]

As you can see his system uses on circ pump for each boiler, and then uses zone valves for each zone. I used a circ pump for each boiler and a circ pump for each zone, including a pump for the indirect heater which is like a zone itself. Works great.

I saw that, but with having only a single heating zone, I'm not sure if I could just get by with the existing pump and one additional pump for the boiler loop. (Wood Boiler will be located, most likely, in my workshop...I'll sub-divide off a boiler-room for it and run pex to the house).

 

[Gasifier]

Lukem. I do not know why I did not post the picture of a system without storage. I probably didn't do that because like b33p3r said above. "There are a lot of very intelligent people........ " I am not one of them! You are probably looking at just adding a wood boiler in to existing system and keep it lower cost for now. At least that is what I gathered from your post. Here is the one without storage.

OOOOhhhh. And definetly read the theory of operation part of that sticky!

And Nofossil. Thanks for posting that stuff man. I used that to show my boys exactly what I wanted and ended up with a saweeet system. You da man!

 

[Nofossil]

Glad that it helped. I posted it out of sheer laziness - a picture saves posting a thousand words of explanation.

 

[Gasifier]

I saw that, but with having only a single heating zone, I'm not sure if I could just get by with the existing pump and one additional pump for the boiler loop. (Wood Boiler will be located, most likely, in my workshop...I'll sub-divide off a boiler-room for it and run pex to the house).

Yes you can. The additional pump will just pump its hot water from WB past PB and to zones. Cooler water will go from zones back to WB. When wood boiler goes cool, reaches a certain low temperature, set on aquastat, your PB will turn on and its circulator will work as normal. With hot water to zone and return to PB. Remember that you want a return protection valve before water reenters your wood boiler. As in Nofossils drawing.

 

[lukem]

I think I have finally wrapped my head around these drawings and primary/secondary...but I think I have a problem. All of these drawings feature zone valves. I have no zone valves in my entire setup...so if I had a circulator running constantly keeping the PB hot, wouldn't it also circulate water throughout the zone potentially overheating the house?

 

[lukem]

I was able to verify that the aqua-stat on the boiler could be set back and the main circulation pump would still continue to run based on demand from the thermostat. The aqua-stat on the boiler was set to 180. I had never seen them run independently before, mostly because the house would warm before it got to full temp...that and the PB hasn't seen much use over the past couple years so I might have just forgotten.

 

[lukem]

I think I have finally wrapped my head around these drawings and primary/secondary...but I think I have a problem. All of these drawings feature zone valves. I have no zone valves in my entire setup...so if I had a circulator running constantly keeping the PB hot, wouldn't it also circulate water throughout the zone potentially overheating the house?

Any thoughts on what to do here, folks?

 

[ewdudley]

Any thoughts on what to do here, folks?

Simplest is usually the 'figure eight' configuration. Connect new boiler supply to old boiler supply and new boiler return to old boiler return. New boiler keeps old boiler hot and all the plumbing and controls for the old boiler heat the house same as ever. You may need some extra insulation and a flue damper on the old boiler if heat loss from the old boiler is a problem. Note this is not boilers in series, the new boiler flows backwards through old boiler. We've seen a few guys do it this way with good results apparently.

 

[lukem]

Simplest is usually the 'figure eight' configuration. Connect new boiler supply to old boiler supply and new boiler return to old boiler return. New boiler keeps old boiler hot and all the plumbing and controls for the old boiler heat the house same as ever. You may need some extra insulation and a flue damper on the old boiler if heat loss from the old boiler is a problem. Note this is not boilers in series, the new boiler flows backwards through old boiler. We've seen a few guys do it this way with good results apparently.

OK...now let me ask you this. Is it still necessary to keep the PB "hot" all the time if it is not making my DHW? I have a stand-alone propane fired 40 gallon water heater for that. I've read some old posts that alluded to that being the reason to keep it hot all the time. I guess thermal shock of dumping 180ish degree water into a cooler, but still not cold boiler, cold be a concern. Is that valid?

 

[ewdudley]

OK...now let me ask you this. Is it still necessary to keep the PB "hot" all the time if it is not making my DHW? I have a stand-alone propane fired 40 gallon water heater for that. I've read some old posts that alluded to that being the reason to keep it hot all the time. I guess thermal shock of dumping 180ish degree water into a cooler, but still not cold boiler, cold be a concern. Is that valid?

If there was a tankless coil in the existing boiler then that would definitely weigh in favor of using a figure-eight configuration, but normally keeping the PB hot all the time is not something you would want to do.

Keeping the existing boiler hot is the price you have to pay to take advantage of the ease and simplicity of a figure-eight setup. But for many boilers that don't waste a lot of heat up the flue -- like a direct-vent natural gas or propane boiler for instance, or a well-dampered oil boiler, or a modern low-standby-loss oil boiler -- the price of keeping the existing boiler hot can be quite low.

This all assumes you're planning on running without storage. If you are planning on putting in storage or a buffer then the figure-eight might not make as much sense in the long run.