Aftermarket Outdoor reset wiring and return bypass questions

dmxart

I am thinking about getting single stage outdoor reset to add to my home gas boiler hydronic system. I am very familiar with low voltage and electrical wiring, but relatively new to boilers since moving to this house. Looking for some confirmation this will work ok with my setup

Background:

Peerless Boiler MI.05.SV.WPC-05 boiler. Non-condensing 115,000 DOE BTUs Natural Gas. Installed 2004

Cast iron radiators all in one zone with a circulator. Circulator is on the hot side, just after the expansion tank and automatic air bleeder

130degree recommended min return temp per boiler manual

Bypass with ball valve installed from just before return input to just after heater water output, before the expansion tank and circulator

There is no heated water storage tank

1925 foursquare 2-1/2 story, approx 2200 sf heated space. Stone foundation and first floor walls, wood frame upper floors. typically layout. Living room, dining room, kitchen foyer and power room on first floor 2 bedroom/2 bathroom and office on second floor. single bedroom/bathroom on 3rd floor. Partially finished basement with no radiators

New(er) everywhere windows. Decent roof insulation, plaster over lathe walls with no insulation

Climate Zone3 in suburban Philadelphia. Average low temp January is 26F

We keep the house chilly indoors in winter by choice, around 63F

Existing Controls:

Honeywell Aquastat L8148E with Honeywell Home RTH6360D1002 thermostat

B1 output is connected to electric damper which actuates when thermostat calls for heat, then when damper fully open, triggers the gas valve which fires the pilot light and burners

Max temp cutout set to 180F

we generally keep the thermostat at single setpoint all the time, although sometimes will do a slight 1 or 2 degree setback overnight when it isn't really cold out so the radiators kick on in the morning to warm things up a bit getting out of bed.

A few questions

1. Considering this outdoor reset unit, Tekmar 256 (https://www.watts.com/products/hvac-hot-water-solutions/controls/boiler-and-mixing-controls/256) single stage looks like an affordable option. Installing the outdoor temp sensor and output hot water temp sensor is simple enough However, the installation manual doesn’t have a typical connection and ladder diagram to show where it fits into a system. https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/81348-source/639223626220000000/256-d-09.pdf
   
   How should the boiler demand input on the Tekmar be wired into the existing aquastat setup? Do I tee the existing thermostat call for heat T terminal to the Tekmar Boiler demand, and insert the Tekmar boiler contact closure between B1 output on the aquastat and the blue wire to the electronic damper? See diagram.

• Thinking about how the control signals would flow, this seems to make sense
  

if the T-stat calls for heat, T goes low and the aquastat will trigger the circulator relay.

When the outdoor reset sees the boiler demand signal from T go low, it will evaluate the outdoor temp and boiler output water temp sensor inputs and decide whether to fire the boiler or just circulate the hot water.

When the outdoor reset boiler relay closes, connecting B1’s 24vac to the damper, the actuator will open, then provide 24v to the gas valve to light the pilot then the burners

When the boiler water satisfies the Outdoor reset sensor, the boiler relay will open stopping the burners and closing the damper. And the circulator will run until the thermostat is satisfied or until the Outdoor reset demands the boiler again

• If instead I wired the thermostat T wire only to the Tekmar demand, the circulator wouldn’t run unless the tekmar demanded the boiler, so no hot water would be delivered to the radiators when the Outdoor reset is satisfied with the boiler water temp. which doesn’t make sense.

2. For 24vac power for the tekmar, I’d pick up 24V at terminal Z and Common at Tv or B2. The transformer on the aquastat looks pretty hefty so thinking no concern with a 2VA load per the Tekmar spec sheet

3. I am not sure when/how to adjust the bypass ball valve. If I run the system now with the bypass valve closed, the bypass piping just before the T where it joins back to the hot water output from the boiler (green arrow) is warm/hot. However as soon as I open the bypass a little, that point gets cold, which indicates to me that cold return water is flowing around the boiler input and cooling the output water. But I thought the idea is that hot water from the boiler output should be pulled the other way to warm the input side of the boiler? There is no check valve so water can flow either way.

I have a good DVM meter with a temperature sensor that I could tape the black iron boiler input pipe and experiment to see how to get to steady state > 130F. is that the best approach? How long do I let the system run before measuring and adjusting?

Also since this is a manual valve, I suspect I will need to adjust the valve to different settings for the shoulder heating season vs the coldest part of winter? What would be practical, to find one shoulder season valve position and one cold weather position, and just switch at some point when it get cold enough? or will I be able to find one setting to work all the time?

Thanks for any assistance. some pics below for reference.

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