Backup for Outdoor Wood Furnace

Scott-Schradle · December 2014

I recently purchased a place with a Taylor T450 outdoor wood stove. It works great but sometimes I have to be gone for a few days and I hate asking someone else to feed it for me. So I'm looking at options for when I'm away. Here's a little info on the layout;

The stove has two zones plus a domestic hot water coil.
Zone 1 goes to the house. The house also has a LP furnace so even if the stove goes out the house is fine.
Zone 2 goes to the shop. This is also where the well, pressure tank, and water softener are. There is no other heat source for this area. This is my primary source of concern.

I've considered getting a small electric heater for the shop. The room with the well is only 200 sq ft or so, so it wouldn't take much. The problem then is worrying about the water in the stove/lines/domestic coil freezing. I considered glycol, but that wouldn't fix the domestic coil issue, is expensive, etc.

So, my thought was to add a small gas boiler in the shop tied into that zone to keep all the water in the Taylor from freezing and heat the shop. I could rewire the aqua-stat with a switch so that when I leave I change from controlling the draft blower to controlling the gas boiler. I just need to keep things from freezing so I shouldn't need to match the 115,000 btu that the Taylor is rated for.

First question; does this sound reasonable? Any major concerns?
Second question; Can you tie a normal gas boiler (closed system) into the open system that is the Taylor? I think not, but could someone sort of explain why? Laymen's terms....or just say, no...too complicated.

If no, could I just use a heat exchanger?
Third question: Someone suggested I use a 50 or 80 gallon gas hot water heater instead of a boiler. The Taylor has ~400 gallons of water in it, so I'm not sure if a hot water heater would handle that....

Any thoughts or suggestions would be awesome.

Thanks,
Scott

Ironman · December 2014

Where are you located? The chances of an ODWB freezing are usually far less than folks imagine. Most Taylor installs are setup to bring the circulator on only during a heat call. It could be re-configured to keep the circ on constant circulation.

If there is a freezing possibility, it's gonna be in the lines, not the boiler. Taylor's leave the lines exposed where they exit the stove. Get them insulated and heat taped there and most of the chances of freezing will be eliminated.

As far as installing a boiler goes, it can be done, but requires a heat exchanger to isolate the open loop from the closed loop. I don't think that trying to use the boiler to back heat the ODWB is necessary or a particularly great idea.

I do ODWB installs as part of our offerings (headed to one now) and I've seen all kinds of ideas both from the manufacturers as well customers. Sticking to basic hydronic principles always works best.

Look on line for issue 10 of Caleffi's Idronics and read it. Lots of great info on ODWBs from some reall knowledgeable pros.

Scott-Schradle · December 2014

I live in southern MN. Worst temps I've seen are -20 with a -50 windchill, but that's really rare. Below zero is pretty common though, especially overnight. The pipes in the back are insulated, but no heat tape. I can add that easy enough. The circ pump on zone 1 has a switch to always run and I could add another one to zone 2. What about the domestic hot water loop? Do I need to worry about that?

Thanks for the info on tying in a boiler. I appreciate it.

Ironman · December 2014

Same thing: insulate and heat tape it. Get the good heat tape that's self regulating and doesn't require a stat. It's braided on the outside.

I think if you do the above things and add something as simple as a propane wall heater in the garage, you should be okay. Build a box around the pipes with lots of insulation in it.

The only caution is power failures. If your subject to lengthy ones, then a standby generator or glycol would be prudent.

In MN, your temps are colder than here in Shenandoah Valley, so more caution is always good.

Scott-Schradle · January 2015

Thanks Ironman! I'm reading through Caleffi's Idronics now. Very interesting. It's a cold one here today. I had windchill of -37 this morning. It's a good think I have a decent pile of hardwood...

Jbshadow01 · December 2016

hi Scott, im guessing you have figured this out already but, with your system both of the pumps should run all the time, like when you turn the switch on the wood boiler on, both of the pumps start, the way the system is piped when the wood boiler goes out, the gas furnace in the house will warm the water in the piping enough to not freeze the wood boiler or the water in your shop, your water coil is on the outlet side of the furnace correct? The down side is now the water going to the woodstove and the shop now has to be heated by your gas furnace. That being said your house wont get heated until the water in your system is warm enough so the residual heat gets to the house. Your plan of putting a gas boiler in your shop is great, the normal setup would be to set your gas boiler at 120 to 140 degrees then when the wood boiler goes out the gas boiler provides the heat to your house and shop, also protecting your wood stove. my setup has an electric boiler set up at 140, my wood stove is adjustable so i run it at 150 when its moderate outside and 180 when its cold out. if im gone the electric boiler automatically kicks in, that way my house gas furnace isnt taxed with heating everything. btw my electric boiler is set up on off peak, so the electric rate is lower. in my case if they did shut my power off due to a high demand then the gas furnace protects my system.

hot_rod · December 2016

I'd look for a method to pipe the boilers parallel. If you use the gas or electric boiler to keep the outdoor boiler warm, you essentially have a cooling tower

Protect the OWF with a back up generator to run the pump if necessary, or antifreeze if possible, heating it with electricity or fossil fuel will offset any savings from the wood burning.

Backup for Outdoor Wood Furnace

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