Editorial Note & Last-Updated: 2025-08-08
Estimated reading time: 15–16 min
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Why this guide exists

HVAC call-backs drain profit. A smart thermostat that flags problems before a crew rolls can protect schedules and customer trust. The Google Nest Learning Thermostat (4th Gen) adds pro diagnostics, adaptive scheduling, and simple commissioning your team can repeat on every job. This guide shows you how to spec, install, and service it without hunting through PDFs. You can price and pick up the Nest Learning Thermostat (4th Gen) and other thermostats at Revco.

Definition / fundamentals

A learning thermostat replaces a wall stat on a 24-volt control circuit. It senses occupancy, learns set-point habits, and sends heating, cooling, and fan calls to the air handler, furnace, or heat pump. The 4th Gen model is built for fast commissioning, stable low-voltage control, and clear at-a-glance data for homeowners and techs.

What the 4th Gen Nest does in the circuit

• Accepts standard R, C, W, Y, and G conductors.

• Drives low-voltage control inputs to stage heat, cool, and fan.

• Supports a single-wire humidifier or ERV on a dedicated control terminal.

• Connects to Wi-Fi for remote access, scheduling, and alerts.

Where it fits

• Packaged units and split systems with 24 V control.

• Gas furnaces with single or two-stage heat.

• Heat pumps with auxiliary or emergency heat.

• Fan coil and air handler applications that need dependable low-voltage calls.

If you need new cable for a C-wire or a fresh pull, stock up on wire, cord, and cable. For alternate Nest models or bundles, skim Nest at Revco.

External reference: The National Electrical Code (NFPA 70) covers low-voltage thermostat wiring in Article 725. See the NFPA 70 overview.

Why it matters in the field (risk–cost table)

For availability and variants, see the thermostats category or the specific 4th Gen Nest page.

Taxonomy / product types

Compare current inventory on Nest at Revco, and spec jobs from the broader thermostats category.

Step-by-step selection workflow

• Confirm system compatibility. Check the control board and nameplate. The Nest Learning Thermostat (4th Gen) supports most 24 V single or two-stage systems with auxiliary heat.

• Plan power early. If the existing cable lacks a common conductor, pull new cable. A dedicated C-wire gives the most stable performance. Pull from stock: wire, cord, and cable.

• Check accessory load. If you will drive a humidifier, dehumidifier, or ERV, verify control current and transformer VA. Add a relay if the accessory exceeds the thermostat’s output rating.

• Decide on remote sensing. In large or multi-level homes, a remote temperature sensor reduces hot-spot complaints.

• Document the install. Record conductor labels, equipment type, accessory wiring, and Wi-Fi details in your job notes.

• Register your install. Capture the install date and configuration in your installer account for clean records.

ENERGY STAR summarizes typical smart thermostat savings and remote management benefits here: ENERGY STAR Smart Thermostats.

Installation & commissioning best practices

Follow NEC Article 725 for Class 2 thermostat wiring. Keep Class 2 conductors separate from Class 1 circuits or use listed barriers in shared enclosures. Support cable at proper intervals. Avoid long parallel runs next to high-voltage feeders to reduce induced noise. Review the NEC overview if you need a refresher.

Pre-power checklist

• De-energize the air handler or furnace and lock out the disconnect.

• Verify 24 VAC at the control board with a meter.

• Confirm transformer VA covers the thermostat plus accessories.

• Inspect cable for damage or loose terminations; replace with new cable if needed.

Mounting and landing

1. Level and mount the base to a stable surface.

2. Pull slack in the thermostat cable and strip clean conductors.

3. Land R and C first.

4. Land W, Y, and G according to staging and equipment type.

5. Land accessory control on the dedicated terminal and route conductors clear of sharp edges.

6. Torque terminal screws to spec and tug test each conductor.

Commissioning workflow

• Power the system and open the installer test menu.

• Verify fan, heat, cool, and accessory calls.

• Connect to Wi-Fi and confirm the app sees the device.

• Set initial schedules or choose adaptive start.

• Enable alerts and service reminders.

• Share a one-page quick-start with the homeowner so critical settings stay intact.

If you need a second device or a backup unit on the truck, grab another from the Nest page.

Troubleshooting cheat-sheet

For replacements or alternates while you diagnose, browse thermostats.

Contractor-focused FAQ

• Do I need a common wire?
  Many jobs run, but a C-wire gives the most stable performance, especially with heat pumps and IAQ accessories. Plan ahead and carry extra thermostat cable.

• Can the thermostat control a humidifier or ERV?
  Yes. Use the accessory terminal, verify control current, and add a relay if needed.

• What if the install has only four conductors?
  Pull new cable so you can land a common. This prevents resets and voltage dropouts.

• How do I reduce call-backs in large homes?
  Add a remote sensor to smooth temperature in occupied rooms and tune staging.

• How do I document the job so any tech can service it later?
  Label conductors, snap photos of the board and stat landings, and store Wi-Fi and schedule basics in the work order.

• What code rules matter most for the stat wiring?
  Follow NEC Article 725 for Class 2. Keep Class 2 and Class 1 conductors separated or barriered in shared enclosures. Support cable and protect it from damage. See the NEC overview.

• Can I set conservative staging to protect compressors?
  Yes. Use wider deadbands and time-to-temp settings to avoid rapid cycling.

• Where can I compare Nest options and stock today?
  Start at Nest at Revco or go straight to the 4th Gen Nest page.

Mini case study

Project: Two-story, 2,600-sq-ft residence with an oil furnace, AC coil, and single-stage condenser
Problem: Occupants reported uneven temperatures and nightly short cycling. Old mechanical stat in a hallway near a return grille.
Solution: Installed the Nest Learning Thermostat (4th Gen) with a new C-wire pulled from Revco cable. Added a remote temperature sensor in the primary bedroom. Widened the deadband and tuned the schedule.
Result: Fewer temperature swings, stable overnight operation, and no call-backs after the first month. The homeowner reported better comfort and easier control.

Code & compliance quick-reference

To stage parts for inspection or day-of swaps, browse thermostats.

Procurement checklist

• Nest Learning Thermostat (4th Gen) — confirm finish and quantity: Add to cart

• Thermostat cable (18/5 or 18/8) for C-wire pulls or new runs: Shop wire and cable

• Inline 3 A fuse for the control board if none is present

• External relay for humidifier or ERV control when current exceeds stat output

• Remote temperature sensor for large or multi-level homes

• Screws, anchors, and wall plate for clean swaps

• Cable labels for conductor identification at the air handler and stat

• Job notes template to record Wi-Fi, schedule basics, and equipment configuration

If the exact finish is out of stock, check Nest at Revco for alternates.

Key takeaways

• The 4th Gen Nest Learning Thermostat reduces call-backs with stronger scheduling, sensing, and diagnostics.

• Plan for a C-wire on older homes so voltage stays stable under load. Carry spare thermostat cable.

• Use a relay for humidifiers or ERVs that draw more control current than the thermostat allows.

• Keep Class 2 wiring compliant with NEC Article 725 and follow the installation instructions on every job.

• Stock common parts so crews can finish in one trip. Start with thermostats.

Need it today?

Call Revco’s HVAC control desk at 631-283-3600 or visit any of our six Suffolk County branches. We will pull your Nest kit, load your truck, and register the warranty before you leave.

About Revco Lighting & Electrical Supply

Since 1978, Revco Lighting & Electrical Supply has been helping professionals bring their projects to light—literally. As a go-to source for lighting and electrical products across Long Island, NY and nearby areas, we specialize in supporting contractors, builders, and industry experts with practical solutions and dependable service. Whether it’s a complex commercial build or a simple residential upgrade, we’re here to make sure you have what you need, when you need it.