Outdoor wood boiler and tankless back up plumbing

[Xavier Eastway]

Hello! New to hydronic heating greatly looking forward to your advice to do this effectively. Wondering how you would pipe this setup and if configuration is well ordered, a diagram would be greatly appreciated, trying to keep it simple and tight:

Outdoor wood boiler providing primary heat runs through heat exchanger in utility room, primary loop runs through heat exchanger into a NRCB199 tankess boiler return line (which also contains the primary loop pump and a heat exchanger for DHW). Out boiler supply to a close spaced Tee on the secondary loop then back to heat exchanger with a y-strainer on the way. The idea is for the OWB to heat the radiant and the DHW and the Noritz kicks on when water temp is too low.

Secondary loop has 4 zones, 2 high temp and 2 lower temp for in floor heat. Have alpha2s for each zone.

Need a bypass for summer on primary when not running OWB so the combi boiler can heat DHW by itself without heating the OWB HX. Also need a mixing valve after OWB HX to tapper the temp down to 165-170 so it can go into the combi boiler not to hot, it has max temp of 180, figured to have OWB at 185 but maybe that can be turned down to 175 and still be efficient.

OWB tubing comes in from upper left corner of mounting wall. Combi Boiler supply port is on bottom left, return is on bottom right, zones go out to the right. OWB is 1-1/4" PEX. OWB HX is 5x12 with 1-1/4" NPT. Noritz boiler is 1" NPT. Presuming on using 1-1/4" copper for primary and secondary loops. Have Amtrol Radiant Extrol - 4.4 Gal exp tank.

1) What would this piping diagram look like?

2) Am I missing anything?

3) Any suggestions on how to prevent the Nortiz boiler from short cycling from the moment demand hot water is needed until the heat from the OWB HX gets cycled through the boiler and it turns the burns off? Called manufacturer, they were not particularly helpful in suggestions.

4) Do I need a mixing valve to place after the OWB HX to protect boiler? If so what would be some recommendations. Also type of mixing valve for the 3rd and 4th zones? Do I need an actuator or just use the mixing valve?

5) Where to put the purge valves/drains? Thought about using Purge & Fill Ball Valve w/ Hose Drains but not sure if that's necessary.

Thanks in advance!

 

[Dana]

Is your wood boiler system even pressurized? (The minimum operating pressure of the NRCB199 is 15psi.)

Can you draw a schematic of what the system looks like right now? It's a bit hard to grasp from the written word alone.

 

[Sponsor]

 

[Xavier Eastway]

Dana, no the outdoor wood boiler is not pressurized. It is separate from the primary propane boiler loop by heat exchanger.

Here's a drawing.

I didn't draw it in but the domestic runs through the propane boiler as there is a heat exchanger inside there to transfer from the radiant heating loop to the domestic.