Adding backup automatic heat source to OWB setup

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Burning Hunk
Feb 24, 2014
I built my house starting in 2004, over a period of a couple years; we moved in during December of 2007. The house is a 2-story timber frame raised-post cape with full finished basement. About 4300 sf of finished space.

Just after I started construction, I installed a 2004-vintage Central Boiler CL5648, bought new as a Dual-Fuel propane and wood setup. I use the OWB as my only source for both heat and domestic hot water, so it runs more-or-less 365 days per year. I would estimate I use the propane, either as a backup or on purpose, about 20 days of the year. The rest of the time I have wood in it. I have no other backup heating source, the only thing that is in my house is a 40-gallon indirect-fired hot water storage tank with a circ pump, for DHW. All of my flow from the OWB goes through a flat-plate exchanger and is split up into several zones for the house and one zone for DHW.

I have come to realize that I cannot work with this situation forever, for several reasons. If I get hurt or somehow incapacitated; if the boiler breaks down or needs extensive maintenance and I can't use it for more than a day or two; or if I am on vacation and can't feed the system, etc.

I would like to find a way to install some kind of backup system in the basement of my house, so that I can eliminate (or abandon in place) the duel-fuel gas burner on my OWB (it's horribly inefficient anyway) and use the backup when I cannot feed the OWB with wood. I have also realized that my OWB won't last forever (it's already developed a minor leak) and if I replace it, I won't have the duel-fuel option. It will most likely be a gasifier unit and much more efficient.

I am looking for opinions on what might be a good backup system for me, without costing a huge amount of money (my budget is around $2000 max) and how I would configure it to my system. I have considered using the following so far:
  1. Tankless-style electric heater, hooked up to the indirect tank supply line, so that when the incoming water temperature gets below a certain setpoint, the heater kicks on and heats the water going into the tank. This would obviously have no effect when the OWB is running, as the water temperature would already be high enough.
  2. Replace the indirect tank with an air-source heat-pump style system (GE Geospring hybrid-electric or similar) and program the heat-pump to kick on if the supply temp is below a certain point. I really like this idea because it would normally be used the most during the summer months, when I'd like to shut the boiler down, and the cooling and dehumidification features come into play.
  3. Install a full blown backup gas boiler in the basement and plumb it in to the main loop. This is not really viable for both cost and space concerns.
Obviously I'm going to need an experienced plumber/HVAC guy for this - I do not have the expertise. I'm looking for ideas and suggestions right now.
You will need much more money than that for an upgrade.

But saying that I have a used Buderus Logana G205 boiler for $1,000.00
that was used only as a backup heat could be converted to gas
that I would sell you as long as you pay for the shipping.
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