Short definition
A mixer faucet is any faucet that combines hot and cold water inside the body and delivers them through a single spout. In British English it’s called a mixer tap. In US homes it’s just “the faucet” — virtually every modern kitchen and bath faucet qualifies. The opposite is two separate pillar taps, each delivering one temperature (rare in modern US homes).
What it is
Inside the mixer body, hot and cold supplies meet at a control mechanism — a cartridge, a ball, two ceramic discs, or a pair of compression stems — that proportions them based on handle position. The blended water exits the spout. The same principle covers single-handle and two-handle designs as long as both temperatures share one spout.
In the UK, plumbers distinguish two sub-types: bi-flow mixers (hot and cold ride separate channels until they meet at the spout exit, used where a vented hot-water cylinder feeds at lower pressure than mains cold) and true mixers (full mixing inside the body, requiring equal-pressure feeds). In the US, all residential mixer faucets assume balanced supply pressure, so the distinction rarely matters.
Why it matters to a homeowner
The term is most useful as vocabulary clarity when reading mixed UK and US plumbing literature, or when shopping internationally. If a product page calls something a “mixer tap,” it’s a regular faucet.
The one place the distinction matters in the US: a faucet that connects two water sources — say, a tankless heater and a recirculating loop — needs check valves to prevent cross-feed, where pressure differential pushes hot back into the cold trunk or vice versa. Most off-the-shelf mixer faucets have this protection built in; oddball multi-source plumbing situations may need it added.
Common variants and what it isn’t
- Mixer faucet vs. two pillar taps. Pillar taps are separate hot and cold faucets each with their own spout. Common in pre-1960s UK and very old US installations.
- Mixer faucet vs. mixer valve. Mixer faucet is deck-mounted on a sink. Mixer valve is in-wall, behind a tub or shower. Same principle, different mounting.
- Mixer faucet vs. tempering valve. A tempering valve is a mechanical pre-mixer at the water-heater outlet (ASSE 1017) — it conditions water before it reaches the faucet, not at the faucet itself.