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Author Topic: outdoor wood boiler?  (Read 9440 times)

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Offline stumper

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outdoor wood boiler?
« on: July 12, 2008, 10:02:10 AM »
I have an oil fired, water base board system and am confused as to the best conection method.  Some say de-pressurize the base board and connect direct.  Other say keep them seperat and install a heat exchanger.

Which is better and why?

Thanks

Offline beenthere

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Re: outdoor wood boiler?
« Reply #1 on: July 12, 2008, 10:58:58 AM »
Can you get your present base-board system to work properly with it open (de-pressurized)? 

Mine won't move the water around unless it is completely free of air trapped in the system, so believe it needs to be pressurized and the boiler water degassed, with a tank to trap air.

I'd suspect that would be why the heat exchanger is suggested.
I added the wood boiler, and kept the pressurized system. Not sure that is possible with the outdoor setup.

I can operate both in series, or separately on only wood or only gas (originally was oil-fired and thankful those days are in the past).
south central Wisconsin
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Offline woodmills1

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Re: outdoor wood boiler?
« Reply #2 on: July 13, 2008, 07:28:55 AM »
My system is hot air, but would think that an exchanger would allow you to continue to use your existing system as is on the times when you are not burning wood.  That is if you depressurize will your existing oil fire work if needed?

I like the fact that I can still use my oil burner and existing hot water when I am not home.
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

Offline treenail

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Re: outdoor wood boiler?
« Reply #3 on: July 13, 2008, 03:05:36 PM »
Installed an outdoor boiler three years ago, and used a heat exchanger to separate the pressurized oil boiler and baseboard system from the non pressurized wood boiler . This was intended so that the oil burner would kick in and keep things from feezing if for some reason one was not home to refill the wood boiler.  Works great and still get the convenience of the baseboards/thermostat.
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Offline JSNH

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Re: outdoor wood boiler?
« Reply #4 on: July 13, 2008, 08:49:28 PM »
I put one in last year and run unpressurized. It works great. For my barn/workshop I have a 70 plate flat plate heat exchanger in line one side unpressurized from boiler the other pressurized antifreeze. I like the unpressurized due to it is a bit more simple but the experience with the heat exchanger has been positive. Either will work.

Offline jackpine

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Re: outdoor wood boiler?
« Reply #5 on: July 13, 2008, 10:09:33 PM »
There is also at least one manufacturer of pressureized outdoor boilers ( Aqua-Therm ). This would allow you to connect directly to your existing baseboard system but has been mentioned above going thru a heat exchanger allows you to isolate each system which has many advantages.
I have an Aqua-Therm boiler and have been happy with it except it could use shaker grates  as the slots in the grates are too narrow and the ashes do not fall thru like they should. I have to rake them back and forth until they do. There is an auger to remove them from under the grates.

Bill

Offline stumper

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Re: outdoor wood boiler?
« Reply #6 on: July 14, 2008, 06:48:26 PM »
I wish I could use the Aquatherm but they do not have a model legal in the State of Maine

Offline splitter

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Re: outdoor wood boiler?
« Reply #7 on: July 14, 2008, 07:50:04 PM »
stumper, I put in a Heatmor three years ago, put a heat exchanger in my A/C (forced air) unit this allows me to have two seperate systems can change back to hot water (oil) and cut off the forced air with a switch and two ball valves in case I get sick and can't get wood. Good Luck------Splitter

Offline jokers

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Re: outdoor wood boiler?
« Reply #8 on: July 16, 2008, 02:29:16 PM »
I`ve got a Heatmor, been using it for ten seasons now if my figurin' is right. Mine is piped directly into the return pipe on my pressurized propane boiler with an isolation valave on both the inlet and return to the Heatmor and another between the legs so that I can zone the wood fired boiler in or out, as I have in summers past.

My system becomes a non-pressurized system when the Heatmor and gas boiler are coupled but both are still functional, the only thing that I have to do differently is close the auto make up valve(water) on the gas boiler and I set the aquastat as low as it will go, which I believe is around 95 degrees. My propane boiler will and has fired normally in the event that I can`t get home to keep the Heatmor going, the downside is that efficiency takes a hit because the gas boiler circulates and heats the water in the Heatmor as well as it`s own water if the fire is allowed to go out.

The upside is that I have freeze protection without the use of any expensive and potentially toxic antifreeze, which also significantly reduces thermal transfer efficiency, by as much as 60% by some accounts. I also saved the few hundred dollars that a heat exchanger would cost. I do have two circulating pumps, the original with the gas boiler and another to circulate the water in from the Heatmor. I simply tapped into the pump relay on the gas boiler which in turn controls a cheap 120v relay for the Heatmor pump. Works pretty well.

Offline Engineer

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Re: outdoor wood boiler?
« Reply #9 on: July 18, 2008, 04:07:33 PM »
I have a Central Boiler which is unpressurized.  I have mine running through one side of a plate heat exchanger, and the other side of the loop, in the basement, is pressurized.   Not sure there's any other way I'd want to do that; if I had problems with my boiler I could just shut that loop off and pipe a different heat source into the heat exchanger.

Offline WH_Conley

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Re: outdoor wood boiler?
« Reply #10 on: July 18, 2008, 09:13:12 PM »
How much pressure are we talking? After a point we are talking about something above the average homeowners ability to handle. I know that I am not qualified on pressure vessels.
Bill

Offline jackpine

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Re: outdoor wood boiler?
« Reply #11 on: July 18, 2008, 10:25:46 PM »
WH, The Aqua-Therm boiler runs at 10 to 12 psi, which is about the same as a home hydronic system if I remember correctly. Pressure relief is set to blow at 30 psi and over temp relief is set to blow at 210 so there is little danger of a boiler explosion. In my experience the main problem with a pressurized system is the swing in pressure at startup due to air trapped in the system as the water cooled on shutdown. You have to bring the temp up very slowly so that the entrapped air has a chance to bleed off, otherwise the pressure will spike high enough to open the pressure relief. You don't have this problem in a home system which has less water and is not heated to the same high temp as the outside boiler.

Bill

Offline jokers

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Re: outdoor wood boiler?
« Reply #12 on: July 20, 2008, 12:57:19 PM »
Jackpine, don`t you run an air scoop with an auto vent on your system? They`re pretty much standard fare on any systems that I`ve seen or dealt with.

What temperature are you running your Aqua Therm versus the original boiler that I`m assuming you have in your house? Hydronic baseboard systems are normally sized based on a specific gallon per minute flow at 180-190 fluid temperature, if your outside boiler runs hotter than this, just how hot is it?

BTW, a thermal expansion tank is used in typical hydronic systems to prevent the relief valve lifting pressure surge that you speak of. The relief valve lifting on system heat up is indicative of a water logged expansion tank or an oxide buildup in the pipe to the expansion tank.

Offline jokers

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Re: outdoor wood boiler?
« Reply #13 on: July 20, 2008, 01:01:51 PM »
I have a Central Boiler which is unpressurized.  I have mine running through one side of a plate heat exchanger, and the other side of the loop, in the basement, is pressurized.   Not sure there's any other way I'd want to do that; if I had problems with my boiler I could just shut that loop off and pipe a different heat source into the heat exchanger.
Why couldn`t I do the same thing in regard to piping in a different heat source, I provided for isolation? I can also run my outside boiler at a lower temperature because I have no Hx efficiency issues to overcome.

Offline jackpine

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Re: outdoor wood boiler?
« Reply #14 on: July 22, 2008, 09:37:02 PM »
Jokers, Notice I said bring the temp up slowly to prevent opening the pressure relief. IAqua-Therm provides an automatic air bleed and a small expansion tank but the volume of water in the boiler is much greater than that in a gas fired hydronic system and if you have a good fire going you bring the water temp up faster than the air bleed can handle. With a small fire the system heats up fine.

Bill

Offline rowerwet

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Re: outdoor wood boiler?
« Reply #15 on: October 21, 2008, 12:20:40 PM »
I went with a HX on my CB Maxim pellet boiler so I could keep the baseboards pressurized as non of them have bleeders, my system uses a taco airscoop and works just fine. if I had bleeders on all my baseboards I would have gone without the HX.
   My brother in law in PA didn't want do deal with any connections to his house system so he just put radiators in his basement and heat vents up into his house, not the most efficient but he own 15 acres and doesn't have to pay for his wood. He has a CB OWB.
josh.
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