Upgrade: 2 Trol-a-temp Model MABS-2 to 1 HZ432 and Nests (hydroair, 1 boiler, 2 handlers, 4 zones)

Donahue1187

Objective:
Replace the 4 thermostats with 4 Nest Learning Thermostats. I bought the HZ432 control board thinking I could also replace the two control boards and wire both air handler/compressors to one HZ432 and have the 4 Nests control the 4 zones. Set up is below, Is there a better way to do this? Do I need to buy a second control board and just replace the two I have like-for-like and wire the 2 Nests to each? At some point in the future I would like variable fan control, so likely would replace the compressors. Really appreciate any advice here!!!

Current set up:

Hydro air system. Single stage heating and cooling.

Boiler 1 (Burnham Low Pressure Boiler RS113C-TB)

***1st floor, 2 zones, 2 thermostats***
Control board 1 (Honeywell Trol-a-temp Model MABS-2 422041-2)
Air handler 1 (Basement, MagicAire 036-DUX-A-4-3HW)
A/C compressor 1 (Guardian GAW14L36C22SA)

***2nd floor, 2 zones, 2 thermostats***
Control board 2 (Honeywell Trol-a-temp Model MABS-2 422041-1)
Air handler 2 (Attic, MagicAire 036-DUX-A-4-3HW)
A/C compressor 2 (Bryant 561CJX036000ADAA)

By the way, I acknowledge this equipment is very outdated, but it has all been very well maintained and inspector claims they'll last several years, if not a decade with good maintenance.

Ironman

How how about posting some pics?

One problem right off of the bat is the Nest. They are the absolute worst stat to use with hydronics.

Jamie Hall

Indeed. Step one -- don't use a Nest. in fact, don't use any power stealing thermostat. If you really need the world to know when you are home and all that, there are other battery or independently powered temperature control devices (I refuse to call them thermostats) which can be used.

And then -- you just swap the new whizbang in for the old thermostats.

Donahue1187

Control 1 basement

Control 2 attic

Boiler

Big picture

Donahue1187

Control 1, Zone 1, faceplate

Control 1, Zone 1, backplate

Control 1, Zone 2, faceplate

Control 1, Zone 2, backplate

Control 2, Zone 1, faceplate

Control 2, Zone 1, backplate

Control 2, Zone 2, faceplate

Control 2, Zone 2, backplate

Donahue1187

@Jamie Hall @Ironman Thank you both for responding here, especially on Xmas Eve (happy holidays btw!). Totally hear you, Nest presents challenges. After lots of research, I decided to go with Google as my smart home platform despite drawbacks of some individual components. So, unless it's actually impossible, Nest is my default for now. Plus who doesn't love a challenge. :-)

Jamie Hall

The challenge is making sure that the Nest is always powered, and that you set its options to play well with your system. I would very much suggest that you look in the manuals first, to figure out independent power supplies for the various Nests you have (I know, wall warts are ugly -- but figuring out how to wire a power source off almost any control board without letting the smoke out can be really challenging!). Then, go through all their settings, and make sure that what you have chosen will work properly with your system. They are splendidly set up for forced air -- but they can be made to work with both hot water and steam, but it's not their preferred approach, so you have to take a pretty deep dive into the settings.

Donahue1187

@Jamie Hall thank you for the feedback!
@Ironman I’m set on using the Nest so hoping to make this work. Would greatly appreciate your perspective based on the photos if you’re willing!!

pecmsg

Donahue1187 said:

@Jamie Hall thank you for the feedback!
@Ironman I’m set on using the Nest so hoping to make this work. Would greatly appreciate your perspective based on the photos if you’re willing!!

Get back up T-stats for WHEN the NEST disappoint you

ratio

With two separate air handlers, you'll need two separate control panels. IIRC HZ311 is a (n up to) 3 zone single stage panel, the HZ4321 is their flagship. It'll work, but it's got a lot more than you need. The panels have common terminals for each thermostat, as long as you use all 5 wires & use a large-enough xfrmr you shouldn't have any power issues.

I don't see any pics of your zone actuators. You may have some creative wiring ahead to reuse them, but I found a schematic on the internets a few years ago—search my old posts for "trol-a-temp" to see how to do it.