Do I need a mixing valve?

[NewBoiler]

I am installing a Kerr TW 2000 wood boiler into my existing system (oil boiler- baseboard-cast iron rads). There is currently no mixing valve used with the oil boiler (Slant/Fin). The wood boiler will be plumbed per Kerr specs, plumbing the wood supply to the oil return and wood return from the oil supply, essientually cycling hot water between the two boilers. The wood boiler needs at least 140 degree return temp to stop condensing issues (manual).

I was under the impression that mixing valves are only used with infloor heating where lower temperatures are used but the manual mentions that they may need to be used with cast iron rads. I currently do not have any mixing valve with the oil boiler.

Do you think I should be using a mixing valve with this setup? Should I use one between the wood boiler supply and return to increase the return temp?

 

[NewBoiler]

I'm thinking I do need a mixing valve. I was thinking of installing the mixing valve in the return line with a ball valve to the supply as shown in the attached pic. Should the mixing valve be installed before or after the circulating pump in the return line?

 

[stee6043]

I think the most common arrangement is to have the mixing valve before your circ pump. My primary circ is 6-8" away from my boiler return and my Danfoss valve is prolly another 12" further upstream.

 

[NewBoiler]

That makes sense because the pump will circulate through the boiler while the mixing valve is closed to the system. Thanks