Off Grid Propane Fired Radiant Heat

26 Posts
Dec 29, 2010 10:07 am
Off Grid Propane Fired Radiant Heat

Hello All,
I'm in the process of hooking up my radiant heat system for my off grid home and had a couple of questions.
A quick run down of my system:
1.2k array
900 amp hour battery bank wired @ 24v
4000k inverter

I am installing a closed loop system. One zone with two 200' loops (in slab) to be fired by a propane on-demand unit (Tagaki jr2 or a Navien 180, havn't decided yet).
Does anyone know what type of circulator pump would work best for this system? I was thinking of a 24v dc pump. Anyone have preferences over brand and/or type?

I also thought hooking up the thermostat to the circulator pump would be the best way to run the system since the on-demand unit is activated by flow. Any suggestions/ recommendations/specs, etc. on that would be helpful especially a link to a diagram.

Thanks for any input.
Dave C
99 Posts
Dec 29, 2010 11:06 pm
Re: Off Grid Propane Fired Radiant Heat

I use a Takagi TK-Jr and it works great.  I have an open system so that the TK-Jr heats both the radiant floors and DHW at the same time.  I have 10 zones, each with their own DC pump (El-Sid 20W).  I built a custom control panel with 12V relays in order to use millivolt programmable thermostats. 

My only issue has been that a single zone pump is on the very edge of enough flow to turn on the TK-Jr.  Currently, it comes on only if two zones are asking for heat, which usually works out fine.  An alternative is to add a booster pump that comes on when any zone turns on.  I actually just finished doing just that today -- the booster pump recirculates hot water to the fixtures (I'm going to also put this pump on a motion sensor in the bathrooms). 

Although the propane has been working out great, this is actually my back-up heat source.  I'm working on putting in a solar thermal system which will be the primary hot water source.  The TK-Jr will only come on when the hot water tank isn't hot enough.
26 Posts
Jan 5, 2011 08:44 am
Re: Off Grid Propane Fired Radiant Heat

Thanks for the input. I have decided to use one larger on-demand unit to do both my radiant and domestic hot water and incorporate a heat exchanger in the loop. This would require two pumps (grundfos alpha series) controlled by one thermostat/ relay.
My radiant system is also backup heat but will be the main source for the remained of construction. We'll build a masonry heater in the spring/ summer.
The Takagi H2 seems to fit the bill nicely and with it's condensing feature I can run PVC pipe instead of stainless class 3 for the vent.
What are the components of your custom 12v relays/ thermostats?
99 Posts
Jan 5, 2011 12:34 pm
Re: Off Grid Propane Fired Radiant Heat

Unless you have very significant demands, a larger unit should not be necessary.  I have a 3200 sqft house and the TK-Jr can easily heat many zones simultaneously while still providing hot water.  I do this by setting the thermostat on the unit at 167 degrees.  Each of my 10 zone pumps pushes about 0.5 - 0.8 GPM.  The TK-Jr can handle up to 5 GPM.  The low flow is sufficient at the high temperature and is actually more effective.  Hotter PEX gives up its heat more easily and it sits in the pipes longer this way.  A high-flow pump at low temperature would take a long time to deliver heat to the floors.  And on the DHW side, I have a mixing valve to bring the temp down to 115 to prevent scalding.  The additional cold water mixing in lowers the flow required through the hot water heater for each fixture.  So a shower calling for 2 GPM (at 115 degrees) might only need 1 GPM through the TK-Jr (at 167 degrees).

I would highly suggest going with the TK-Jr and see if it meets your needs.  You can T off your plumbing for a future 2nd TK-Jr side-by-side if you really need more flow.  Since the TK-Jr costs about $500 vs $1500+ for the H2, this would be the more economical method.  Also, if you do need the additional unit (which I doubt you will), then it'll be a nice redundancy to have two in case one fails.

I used 12VDC automotive relays to trigger my pumps via the millivolt programmable thermostat signals.  For each zone, I added an LED to indicate power on / heat not called for, another LED to indicate heat being called for, and then a toggle switch with another LED to indicate the pump is actually running and as an emergency cut-off.  I put these in a wooden box with the LEDs and switches coming through the front face and added a couple of fuse blocks so that each thermostat is protected by a 1A automotive fuse (I'm powering the thermostats off my house batteries so I don't have to change out AAAs) and each pump by a 3A fuse.
1 Posts
Feb 21, 2012 10:34 pm
Re: Off Grid Propane Fired Radiant Heat

I'm looking to discuss some questions with Thomas Anderson....anyone know how to reach out to him?


thank you.
99 Posts
Feb 22, 2012 08:30 am
Re: Off Grid Propane Fired Radiant Heat

I'm looking to discuss some questions with Thomas Anderson....anyone know how to reach out to him?

You can message me here or email me: altestore {at}

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