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[Belknap]

I am getting ready to install an OWB this summer.  I got my grapple load of wood and got that all cut.  I am trying to get ready for the plumbing part of the install.  This is for my barn.  I have six zones of radiant heat and domestic hot water.  I have attached a sketch showing my current heating system with a gas wall hung boiler.  I am just wondering if I can just extend off the manifold to a plate exchanger and run the system pump that is currently there 24/7 through the wall hung boiler or do I need to be able to bypass the wall hung boiler when not in use?  That boiler is 225,000 BTU wondering what size plate exchanger I should use?

The barn is new construction with 2x6 walls and good insualtion.  The size is 60 x 44 two floors.  I have radiant in the slab on the first floor and under the wood floor on the second floor.

I would greatly apprciate any help with this.  If I am leaving out any information let me know.


Thanks

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[Scott7m]

Woodmaster and others recommend going with a plate nearly double what your rating is, I would probably be looking at an 80 plate or bigger perhaps..

As far as the other unit, not sure about it by the diagram

[RSI]

For in floor heat you can use a much smaller heat exchanger because of the delta t you are working with. A 30 or 40 plate is probably plenty. If you were heating baseboard or radiators you would need it to be much larger.
I would use at least 1-1/4" pex to the building if you intend to draw 225k btu off the system, otherwise your return temp will probably be really low.

I can't see the diagram very good on my laptop. I will try to remember to take a look at it at the office tomorrow.

[RSI]

Just put the plat in series with the wall hung boiler. If the pump is running 24/7 it will keep it working like it is currently. If you intent to leave the wall hung boiler running as auto backup, you will either need to turn the temperature way down or use an aquastat to disable it to make sure the gas doesn't fire when you don't need it.

[Belknap]

Thanks Scott and RSI for the response.  I will probably just turn the temp on the wall hung boiler down and use it as emergency back-up.  When you say put the plate exchanger in series you just mean to extended the supply and return manifolds and install the plate exhanger there correct.

[RSI]

I would cut into the return pipe to the wall boiler and put it in series with that pipe. You will want the hottest water to always circulate through the boiler so it doesn't come on and reheat ever. From there, the ot water will go through the system as it always has.

[Belknap]

That makes sense.  Thanks.  In the house I have a conventional boiler and I am planning to do the same thing but I have baseboard heat there.  That boiler is 115,000 BTU?  What size plate would I need for that and I was planning to use 1" pvc.  The run from the boiler to the house is 180 ft.

[RSI]

PVC all the way to the boiler?
Regular PVC won't take the heat. CPVC will but unless you have a reason for using it, I would use pex instead. It is a lot stronger. CPVC is much more brittle and can get broken a lot easier.

The size you will need depends on the total length and the size pump you intend to use. Going with larger pipe will allow you to use a smaller pump.

[Belknap]

Sorry.  I meant pex.  I am an electrician not a plumber.

[Belknap]

I think I will use logstor underground piping.  Is the 1" big enough.  I have read that the 1" is pretty close to 1 1/4" pex.

[Scott7m]

The 1" logstor is true 1" inside.  It should work well

[Belknap]

I just had a few questions.

My  gas boiler is on demand so the temp in the boiler can get down to say 40 if nothing calls. There is freeze protection so it won't freeze but if I hava a heat exchanger close to the boiler the temp in the heat exchanger will be say 175 because the pump on the owb will run 24/7.  When a zone calls the temp in the gas boiler can be below the firing temp of 150 so the gas boiler will fire.  Will the heat exchanger keep the gas boiler temp warm enough just from radiation in the water so when a zone calls the gas boiler won't fire?

I have to keep the gas boiler on because the system pump and the DHW pump are controlled by the gas boiler.  When the DHW or any other zone calls the gas boiler fires and it powers the system pump and the DWH zone pump.

Thanks