Wood Boiler Plumbing

[Mark M]

I am in the process of installing a wood boiler. It will go in the garage and hook in to my existing gas boiler system with cast iron radiators. I am a little stumped right now and thinking about some different options. I want to use antifreeze in the wood boiler but am reluctant to add it to the current system because I am concerned about developing leaks, pumping problems, heat transfer efficiency, etc. What I would like to do is use a heat exchanger and put antifreeze in the wood system and use water in the existing system. Problem is I am not sure of the best way to go about doing this. I've looked at the Central Boiler site and they have some good information but it is a little different than my system. I'm also concerned about thermal shock from putting cold water to gas boiler.

Any suggestions?

How did you plumb your system?

What about controls?

If you are using antifreeze what type and brand?

Thanks

Mark

[Den Socling]

Mark,

Look at brazed plate heat exchangers. They make a huge transfer in a small space and they are relatively cheap.

Den

[Mark M]

HI Den

I have been looking at some of those by FlatPlate Co. I am a little confused about the sizing. The existing boiler is rated at 164,000 BTU and the wood boiler at 150,000 BTU. At the FlatPlate site they talk about "Close Approach" ratings which is a new term for me. From what I can understand it refers to the temperature drop from one side of the exchanger to the other. Problem is I don't know what is a reasonable drop. Any ideas on what size I would need?

Mark

[beenthere]

I operate a wood 'boiler' and gas 'boiler' in combination or individually depending on my time to fire the wood boiler.
There is an 'antifreeze' called Cryo-tek and I looked it up at this site
http://www.herchem.com/Products/Cryotek-100Al.htm

Also, I add water manually to my boiler system, and in 35 years have not had a problem with 'cold shock' but always heat the water when added to drive off the oxygen so the boiler cast will not rust (its why I prefer the non-automatic system of adding water if low).

I have valves to switch the water flow from the gas to the wood boilers, and as well have a switch to run gas alone, wood alone, or both in series. In series, I sense the water temp coming from the wood boiler, and if it drops below 100 F, then the gas will kick in to bring it up at least to that temp. That is in case I am not able to put wood in, and don't get the systems manually switched over to gas.

The system is closed, and there are three thermostats operating three pumps. It works well.

[Mark M]

Hi Beenthere

Any chance you could draw me a picture?

Mark

[beenthere]

Now that drawing thing IS a challenge!  But, in the interim, I took a picture and will see if that helps, and will try to draw in the flow along the pipes from (and to) the wood (left) and gas (right) boilers. The three red pumps are in the middle of the picture. Also included in the pic (just to confuse) are a stainless steel 30 gal tank in the center that has a coil in it to pre-heat water (using the wood heated water) going to the domestic hot water heater (white - in back).
 Let me know if this helps a bit.
If I was just a bit more adept at the Turbo-Cad program, I should be able to turn out a pretty good drawing. I'll see what I can do.
In the meantime, here is a pic:
 

drawing (old Windows Draw program, not TurboCad):

[Mark M]

Thanks, that helps.

[Den Socling]

Mark,

When trying to guesstimate a size, go by connection size. If your system is 1-1/4, get a brazed plate with 1-1/4 connection.

Den

[Mark M]

Den, can you recommend a source? I just checked with our local dealer and the price they wanted was from about $500 to over $800!  

[Den Socling]

Mark,

Maybe your local guy is selling units that are certified for steam. I've been told that doubles the price. I have to buy them when steam is involved. Ask him if he has water to water.

I wouldn't expect McMaster-Carr to have the best price but I checked there. And DanG it if they aren't going by gpm rather than pipe size. A little 5 gpm is $250 and a really big 100 gpm is $1600.

Den

[Typhoon]

I'm building a log home next year. I am contemplating putting in a wood boiler to compliment the gas boiler. Man it is so confusing. I have been studying and studying and still have no idea what I am going to do yet. Didnt even think about putting antifreeze in!! Opens a whole new angle!! Yikes..
 

[karl]

If you get hold of Central Boiler propaganda there are some helpful diagrams.
The salesman found a more economical brand of flat plate exchanger  than the one Central carries. It is made by Energy Kinetics- Lebanon, NJ. the one I have is rated 160,000 btu for around $265.
Controls are- aquastat turns on circulator for wood boiler when water reaches temp.
         aquastat on return line operates circulator through my oil boiler.
       Domestic HW is heated with oil boiler so as long as exchanged heat is above 165 burner won't start, wood is set to maintain 170-185.
    currently no antifreeze, have in the past used No- Burst from heating wholesalers.
  If you are creating a closed system(pressurized) make sure you have pressure and temperature release valves and a "dump zone" or you could have a bomb on your hands!!!!!
Bon Chance

karl