Outdoor wood-fired boilers

D Dreyer

I have been having some requests lately on adding open loop outdoor wood fired boilers to existing indoor gas fired closed loop boiler systems. The perfered method would use the gas fired boiler as a back up system when the wood fired boiler will not keep up. I am thinking of using a plate heat exchanger to tie the two systems together, but am worried about keeping the plate heat exchanger clean when running with a open loop system. I would circulate the outdoor pump continulously using a three way valve to modulate flow through the plate heat exchanger. The heat exchanger would be located in the retun to the indoor boiler. On a call for heat the primiary pump will operate enabling the three way valve to control flow to the heat exchanger on the outdoor side. Any suggestions, am I on the right path or does someone have a better way? I would rather do it right or not do it at all.

kevin

Hi Dwane...

I am having a similar situation, although the outdoor wood boiler that the HO is providing is not an open system type.I still want to isolate the outdoor glycolled boiler from my Buderus boiler. I am piping the boiler primary/ secondary and am going to suggest a stainless steel pool heat exchanger, Weil-Mclain makes a real nice one in a few different sizes.Lots of room and a good flow rate/ low head loss. kpc

hr

You are right

to be concerned about corrosion and the effect on the small HX spaces in a flat plate. You really need to maintain the corrosion inhibitors in those open systems. Sometimes the dealers include a starter bottle for inital fill. Get a test kit and extra chemical.

For the life of the of the outdoor furnace and all the other "A" side components, keep up the inhibitor levels. A tube and shell type exchanger would be another option, keep in mind scale formation will reduce the efficiency, regardless of the type of exchanger surfaces.

Here is an idea for easy descaling of HXs that I use on the DHW side. Get a couple of these Watts valves (available in FIP also). This allows you to circulate a coil clean solution through the hx. Use a five gallon bucket with a small "Little Giant" submersible plastic pump and a couple wash machine hoses to connect and circulate in and out of the bucket, and through the HX.

Also keep the firebox clean, if the ash is allowed to get wet during unused periods it can start to eat away at the thin metal surfaces from the fire side. Happy heating

hot rod

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hr

With open system

outdoor units, be sure to keep up the corrosion inhibitors. This is your best protection for the unit itself, and all the "A" side components. Generally you get a start up bottle with the unit. Get a test kit and additional inhibitor.

Regardless of the type of HX you choose, even a thin scale coating will drop efficiencies considerably. Same with tube and shell type HXs. Same HX surface area, really, just in a bigger enclosure

When I install FP's in domestic water applications, I install a couple of these Watts valves. Available in FIP also. This allows you to run a coil cleaner through the HX only. Use a small "Little Giant" plastic submersible pump in a 5 gallon plastic bucket. A couple of wash machine hoses allow you to circulate cleaner from the bucket through the HX.

Keep the firebox clean of ash also. If the ash gets damp during unused periods it will attack the thin metal firebox from the fireside also. Happy heating!

hot rod

Sorry if this double posts

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Boilerpro

Tekmar Control for this setup

I believe the tekmar 363 control provides a nice slick setup for this application. I've been getting calls for typing in outdoor boilers too here in Northerm Ill.

Boilerpro