Zone Valve Wiring

Zone Valve Information

Zone valve wiring varies with different manufacturers and different models. There are multiple ways you can wire zone valves, but I suggest adding an external 24v transformer or a multi-zone relay for zone valves. Do not wire zone valves to the boilers existing 24v transformer unless their installation manual shows a way to incorporate the wiring into the boiler transformer. When adding external transformers, you must have a transformer rated at 24v and the proper VA (volt Amps).

Before we dive to deep into sizing transformers you can use a multi-zone relay. Purchase the zone relay for the amount of zone valves you have on your system. The zone valve panels will interconnect to accommodate a larger number of zone valves. This will make wiring much easier.

If you decide to tackle zone valve wiring, you will need the following information.
Some model zone valves you can only have 3 on a 24v 40VA (most common transformer) and others is 12 zone valves per 24v 40VA transformer. You can buy a higher VA transformer to handle more zone valves if you decide not to use a zone valve panel. Sizing the transformer VA, you need to get the amp draw off the zone valve power heads you will be wiring. To determine how many amps a transformer can supply or what size transformer is required for the amount of zone valves you are trying to operate is simple.

What does Volt Amps mean?

Volt Amps is the amount of amps that can be drawn from the secondary windings of a transformer
To determine the amount of amps available for zone valves divide VA rating by transformer secondary voltage.

The formula would look like this

Where AA = Available Amps
VA = Volt Amps
TS = Transformer Secondary voltage


A 24v 40VA transformer you would use the following formula:
40VA divided by 24V = 1.6 amps
A 24v 72VA transformer would be;
72VA divided by 24v = 3 Amps for zone valves

To determine required transformer volt-amps, with known amp draw multiply amps x secondary voltage (24v).

The formula would look like this;
VA = A x TS
VA = Volt Amps
A = Amp load
TS = Transformer secondary voltage


Add together the zone valve amperage. Let’s assume the combined load is 3 amps.
3 amps x 24V = 72 VA transformer

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