Can I install this myself?

Yes. Installation requires basic comfort with electrical wiring at your furnace or boiler. Our online guide creates custom instructions for your exact setup with 11 different wiring diagrams. If you're uncomfortable working with HVAC wiring, hire a qualified technician—typically $75–150.

Can I reuse this adapter with a different thermostat?

Only with Mysa Smart Thermostat. Does not work with other Mysa products (Baseboard, In-Floor) or other smart thermostat brands.

Do I need the C-Wire Power Adapter?

Over 55% of compatibility checker submissions need the adapter. Homes built before 2000 and hydronic heating systems are most common.

Does this work with boilers and hydronic systems?

Yes. Works with hot water boilers, hydronic in-floor heating, and zone valve configurations. For zoned systems, install the adapter at each zone valve—not at the boiler aquastat.

Does this work with Mysa for Baseboard or In-Floor?

No. The C-Wire Power Adapter works exclusively with Mysa for Central HVAC. Baseboard and in-floor thermostats use line voltage and don't require a C-wire.

Mysa C-Wire Power Adapter

Name: Mysa C-Wire Power Adapter
Brand: Mysa
SKU: CWA.2.0.01.SV
Price: 25.00 USD
Availability: InStock

Provides reliable 24V power to your Mysa thermostat when no C-wire is available. Installs at your furnace, boiler, zone equipment or air handler.

$25.00

Model

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Pricing details

Mysa C-Wire Power Adapter × 1 $25.00

$25.00

Description

Many homes don't have a C-wire at the thermostat, and running new wire through walls is a hassle. The Mysa C-Wire Power Adapter provides continuous 24 VAC power to your Mysa Smart Thermostat by repurposing your existing wiring. Designed to handle the trickiest installations, including two-wire heat-only and cool-only systems where you have just R and W (or R and Y) at the thermostat.

Check Gas and oil furnaces

Check Air conditioners and heat pumps

Check Hot water boilers with hydronic systems

Check 24V zone valves and zone valve control boards

Check 24V relay configurations

Check Millivolt/dry contact configurations (many fireplaces)

Compatibility

Works with Mysa Smart Thermostat only

Installation happens at your furnace, boiler, air handler, or zone valve panel. Our online guide creates custom instructions based on your exact wiring setup—with 11 different diagrams covering most configurations.

Standard installation (furnace/air handler):

Turn OFF power at the circuit breaker
Locate control board
Label existing thermostat wires using included stickers
Photo your wiring for reference
Reroute wires through adapter following your custom guide
Mount adapter using included adhesive pad
Restore power and verify thermostat displays

Boiler and zone valve systems: For hydronic systems with zone valves, install the adapter at the zone valve—not the boiler aquastat. Multi-zone setups need one adapter per thermostat.

External transformer option: Older boilers or systems without adequate 24V power can use the Rext terminal with a standard 24 VAC transformer (sold separately, ~$15–20 at hardware stores). One transformer powers up to three Mysa + adapter combinations.

Specifications

Model: MYSA CWA V2-0

Input Voltage: 20–30 VAC

Current Rating: 8A (2A max on W/Y/OB)

Operating Temperature: 0°C to 50°C (32°F to 122°F)

Relay Type: Isolated dry contact

External Power: Rext terminal for 24 VAC transformer

Wire Harness Length: ~12" (30 cm)

Ingress Protection: IPX0

Dimensions: [placeholder - to be added]

Colour: White

Warranty + Returns

Our return policy is simple. High utility bills will never return. But if you do need to send your Mysa back, that's simple too - free shipping both ways and expert support at every step.

You expect a smart thermostat to last. After a million units and years of engineering refinement, we know ours do. That's why every Mysa comes with 5-year coverage - more than double the 2-year industry standard.

What's in the box

Features

Bolt Reliable 24V Power

Build No New Wiring

House Two-Wire Ready

Quick_Reference Custom Install Guide

Package_2 Hardware Included

Eco Less E-Waste

Control from Anywhere

"The 4 best smart thermostats of 2025"

~ Wirecutter / New York Times

"Works as expected…finally got rid of the junky 1980’s thermostat that only heated to the max temp"

~ Derek F.

"Does a better job than the other smart thermostats I've used and the app gives you all the information you need to make the best use of your home heating dollars."

~ Ian V.