YDDECW Thermostat Wire - 18/2 20FT Solid Copper 18AWG 2 Conductor Power Circuit Cable for Heating & air Conditioning Equipment, doorbells and Other Indoor/Outdoor Low Voltage Applications Use

What this wire is for—and where it fits

For small HVAC and low‑voltage jobs, I like keeping a 20‑foot coil of 18/2 thermostat wire on hand. This one from YDDECW has been my go‑to lately for heat‑only thermostat runs, doorbell circuits, and quick pickups to outdoor condensing units where only two conductors are needed. It’s a solid‑copper, CL2‑rated, ETL‑listed cable with a brown PVC jacket and two color‑coded 18 AWG conductors inside. On paper it’s rated to 150 V and -20°C to +60°C, which covers typical low‑voltage control circuits comfortably. In use, it behaves like a proper in‑wall, low‑voltage cable: predictable to strip, stiff enough for neat routing, and robust enough to survive fishing through studs and joist bays without scuffing or splitting.

Build quality and materials

The construction is straightforward in a good way. The outer jacket is a smooth, medium‑durometer PVC that resists scuffs and staples without feeling plasticky or brittle. Print legend along the jacket includes the gauge, CL2 rating, and listing mark, which is helpful for inspections or just for your own documentation. Inside are two solid 18 AWG copper conductors with their own PVC insulation. On my coil the inner colors were red and white—easy to identify for an R/W heat‑only setup.

The headline feature here is that the conductors are pure copper, not copper‑clad aluminum. For low‑voltage control runs, solid copper matters less for raw current capacity than it does for long‑term reliability at screw terminals and push‑in blocks. Solid copper holds shape under terminal pressure, and I haven’t seen cold flow or loosening after seasonal temperature swings.

Installation experience

I used this cable to replace a short run from a first‑floor thermostat to a basement furnace control board. The old cable had kinked jacket and nicked insulation near the staples; this was a good test for abrasion and staple resistance. A few notes from the install:

• Pulling and fishing: The jacket slides well over wood and through stud bores. It has just enough stiffness to push across short cavities without a fish tape, but it’s not so rigid that it wants to spring out of your hand.
• Stripping: Using an 18 AWG notch on a manual stripper, the outer jacket scores cleanly with a light ring cut. The inner conductor insulation also strips without tearing or lifting. I didn’t see any tendency to nick copper with normal care.
• Terminations: The solid core seats neatly under screw plates on furnace boards and old‑style doorbell screws. For splices, Wago‑style lever connectors and small wirenuts both grab well on 18 solid.
• Staples and bends: Low‑voltage staples set flush without biting through the jacket. Minimum bend radius is generous; tight 90s around studs didn’t kink the jacket.

Overall, it’s a no‑drama cable to work with, which is exactly what you want for in‑wall control wiring.

Performance and electrical characteristics

For typical thermostat and doorbell loads, 18 AWG is the right balance of size and resistance. DC resistance for 18 AWG is about 6.4 Ω per 1,000 ft; over a 20‑ft run (40‑ft loop), you’re talking well under an ohm, which is negligible for 24 VAC control circuits. On a heat‑only thermostat (R/W), the furnace responded crisply with no chatter, and coil actuation on a doorbell transformer/chime was strong and consistent.

The 150 V rating isn’t about running this at high voltage; it’s a safety envelope that speaks to insulation thickness and dielectrics. For Class 2 circuitry, this is exactly what I expect to see on the jacket. The -20°C to +60°C temperature range covers unconditioned basements and mild outdoor exposures without drama.

Indoor/outdoor considerations

The listing and jacket make this appropriate for in‑wall indoor use and protected outdoor runs. I’ve used short lengths outside between a disconnect and an AC condenser control panel. The jacket shrugged off light rain and dew; the fit and finish inspire confidence for damp locations.

That said, any PVC jacket can be vulnerable to long‑term UV exposure. If you’re routing this along an exterior wall or across a roofline, I recommend running it in conduit or at least using UV‑resistant raceway or paint for protection. “Waterproof” in the marketing sense here means water‑resistant; it’s not submersible cable. Keep splices in proper junction boxes, and don’t bury it directly.

Suitability for modern thermostats

A practical note: this is a 2‑conductor cable. It’s perfect for heat‑only systems (R/W), simple doorbells, and some control applications, but many modern smart thermostats need more conductors (C, G, Y, etc.). If you’re future‑proofing a wall run, an 18/5 cable is often the smarter play. I still keep this 20‑foot 18/2 around for repairs, add‑ons, and situations where pulling extra conductors isn’t necessary or possible.

If you’re running to an outdoor condenser that only requires a simple contact closure, two conductors are all you need, and this cable is a neat, tidy solution.

Handling in the cold

I staged part of the installation in an unheated crawl space just above freezing. The jacket stayed pliable, not glassy, and didn’t crack when bent around joists. Coils do retain a bit of memory out of the bag—as most thermostat wire does—but a quick reverse wrap straightened it without a fight.

Value and packaging

At 20 feet, this coil hits a sweet spot for small jobs: longer than the token 10‑ft “repair” packs, but not enough to leave you storing a bulky spool for months. The coil arrived neatly wound with twist ties and a clean cut on the end. If you routinely run longer distances or are rough‑in wiring a remodel, a 50‑ or 100‑ft spool is more economical; for a furnace jump, doorbell replacement, or condenser hookup, 20 feet is just right.

What could be better

• Sunlight resistance disclosure: I’d like to see explicit “sunlight resistant” labeling if it’s applicable, or a clear note to use conduit for UV exposure. The cable holds up outdoors in protected runs, but UV guidance would help DIYers.
• Conductor count options: This 18/2 is well executed, but many users end up needing 18/5 for a C wire later. Offering a clear path to multi‑conductor variants under the same line would reduce the chance of buying twice.
• Spool option: A mini‑reel would make payoff cleaner. The coil dispenses fine, but a small core would reduce memory in tight cabinets.

None of these are deal‑breakers for the intended use; they’re quality‑of‑life tweaks.

Practical tips from the install

• Leave a service loop at both ends. An extra 6–8 inches behind the thermostat and furnace makes future swaps a lot easier.
• Use low‑voltage staples, not standard cable staples. The former have a wider crown and won’t crush the jacket.
• Label the conductors before you terminate. Even with only two wires, a quick tag on red/white avoids mix‑ups during future service.
• If running outdoors, use UV‑rated conduit or paint the jacket where exposed to sunlight.

The bottom line

This 18/2 thermostat wire does exactly what it should: it’s solid copper, CL2 and ETL compliant, easy to strip and terminate, and tough enough for in‑wall pulls and protected outdoor hops. I’ve had clean installs with reliable operation on both furnace control circuits and doorbell chimes, and the jacket and insulation have held up well to staples, bends, and a bit of cold‑weather handling.

Recommendation: I recommend this cable for any small low‑voltage control job that only needs two conductors—heat‑only thermostats, doorbells, simple condenser control, annunciators, or sensor loops. It’s a dependable, code‑friendly choice with thoughtful construction. If you’re wiring a new thermostat run and anticipate adding cooling or a smart stat later, step up to an 18/5 version; otherwise, this 20‑foot 18/2 is a tidy, reliable solution that installs without fuss and performs as expected.