Three Way Mix Valve Location

[JMann]

I've been talking to several installers for my Seton 90 boiler. Most have not heard of using a three-way mixing valve. Even the engineers at Bethel Engineering (Where they make the Seton) state that it is not needed, however from reading these posts, I'm pretty sure that I should use one (to reduce creosote issues by increasing return temps).
Where should I have the installer place the 3-way?

Here is my setup:

Oil boiler in basement (backup heat)
Radiator heat (water)
30 Plate Heat Exchanger to boiler (basement)
Make up water / expansion tanks (basement)
Side arm Heat Exchanger for DHW w/ Honeywell anti-scald mix valve (basement)
Two Pumps (basement)

Seton is in outbuilding (former garage)
Approx 50ft of exposed pex running in garage
80ft run of Thermopex running to the house
Seton has two aquastats (on the boiler)

Thanks in advance for feedback - I see the light at the end of the tunnel, and I don't want it to be a train!

 

[steam man]

A mixing valve is normally on the return leg close to the boiler. Pipe the outlet of the boiler to one inlet and the returns from the system to the other. Now you can recirc some low temp boiler water until the boiler is up to temp. It seems to me with the way the seton is designed with the exhaust gas exit being heated by the incoming "cooler" water some means of keeping the temperatures up should eliminate some of the creosote, especially on startup and shutdown when most of it occurs. Being a water tube design thermal shock is probably is not as much an issue.

Mike

 

[Tony H]

Could it be the description ? Maybe instead of mixing they would call it a tempering or Thermostatic valve because it is set at fixed level where a mixing is adjustable ? I always call the one on the boiler return a termovar and the one on the output of the water heater a mixing valve. Then again maybe that design has no need to have the return water at a given temp.