Mix valve and sensors - Boiler Scheme for comment

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Maine Way

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Hello All,

I plan to use mixing valves as opposed to injection to mix temperatures for radiant heat.

There is a lot of opinion out there about which is better, but one comment stuck with me that injection is more important for boiler protection for cast iron boilers and mixing valves are a good choice for Mod Con boilers with small systems.

The boiler I have chosen has a number of sensors and features which regulate water temperature in order to maximize condensation. Above this requirement, my system also needs to control water temperature for radiant floors. Most of my confusion revolves around how added sensors and controls will play with the existing ones on the boiler.

I’ve attached a file of the schematic I’ve developed to this point.

1. Lochenvar Knight has an outside reset and regulates water temperature, system pump, turndown ratio (10:1) in order to achieve condensation. And it has DHW priority zoning option. Would these controls be adequate to supply domestic hot water and CI baseboard zones? I don’t need any additional mixing to adjust water temperature for cast iron space heating?

2. For the radiant floor zones I plan to use a taco 1", 3 Way Setpoint I-Series Mixing Valve w/ Sensor or similar. I don’t need any extra controllers with this valve? There is also a valve available that has an outside sensor. Is this important for the system? The boiler already has that and my assumption is that the boiler is tasked with monitoring and adjusting water temperature to maximize efficiency (as cool as possible) and the mixing valve provides a constant, low temperature for the radiant floor. Will the boiler system get confused by the fact that some of the water in the system is mixed with return water sometimes? Or, since the boiler measures supply temp and outside temp and perhaps the length of the fire cycle to satisfy the thermostat, it does not care what happens on the return loop?


  • boiler schem.pdf
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Tuttles Revenge

In the Trades
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Maybe this should be posted in the dedicated Boiler Forum for better visibility. I'm not enough of an expert in boilers to give an opinion.
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