In Wall Heater: Complete Guide for Homeowners

A 40-year-old resistance coil behind a rusted grille is still working in houses I walked through last week, which says something about the category. An in wall heater is the most space-efficient way to add supplemental heat to a bathroom, garage office, basement, or addition where extending ductwork makes no financial sense. The trick is matching wattage, voltage, and heat style to the room, not grabbing the first unit at the big-box store.

Main Types of Wall Heaters

Manufacturers lump four distinct technologies under the wall heater umbrella, and they perform very differently in real rooms. Pick the wrong one and you either freeze or listen to a fan roar for six hours straight.

• Fan-forced electric — quick warm-up, most common, 750 to 4,000 watts
• Radiant convection — silent operation, heats objects and bodies
• Hydronic — electric element heats fluid for even, lasting warmth
• Gas-fired — vented or ventless natural gas or propane models

Sizing Wattage to Room Square Footage

The rough rule is 10 watts per square foot for a well-insulated modern home. A 150 square foot bathroom needs 1,500 watts. Bump to 12 watts per foot for poorly insulated rooms, older homes, or spaces with large windows facing north.

Do not oversize. A 4,000-watt unit in a 200 square foot room cycles on and off constantly, burns out elements faster, and creates hot-cold swings. Matching wattage to load is more important than brand loyalty.

Voltage: 120V vs 240V Circuits

Smaller heaters up to 1,500 watts run on standard 120V circuits. Anything larger typically requires a 240V line. Running a dedicated 240V circuit in new construction is cheap, roughly $200 to $400 with an electrician. Adding one to a finished wall with no attic access easily doubles that.

The 240V advantage is efficiency and faster heat-up. A 2,000-watt 240V unit moves twice the heat of a 1,000-watt 120V unit but pulls the same 8.3 amps, keeping you within typical breaker ratings.

Top Brands Worth Considering

Cadet

Cadet Com-Pak Twin and Com-Pak Max are the industry workhorses at $130 to $220. They mount in a standard stud bay, accept field-installed thermostats, and last 15 to 20 years in normal use.

King Electric

King PAW and W series run slightly quieter than Cadet and include smart-limit temperature sensors. Expect to pay $180 to $290 depending on wattage.

Stiebel Eltron

A German-built CK Trend unit costs $350 to $450 but runs nearly silent and uses a better thermostat with degree-accurate calibration. Worth it for bedrooms and bathrooms.

Installation Walkthrough

1. Kill the breaker and confirm with a non-contact tester
2. Cut the rough opening between studs per manufacturer spec, usually 14.5 by 12 inches
3. Pull 12/2 or 10/2 Romex through the stud bay to the main panel
4. Install the mounting can, squaring to the drywall face
5. Wire the heater following the color-coded diagram inside the can
6. Attach the grille and thermostat
7. Restore power and test on low, medium, and high settings

Budget 3 to 4 hours for a first-time install if the circuit exists, plus another 2 to 6 hours for circuit extension.

Operating Costs and Efficiency

A 1,500-watt in wall heater running 6 hours a day at $0.15 per kWh costs about $1.35 daily or $40 monthly during heating season. That is competitive with baseboard electric but more expensive than a heat pump at equivalent output.

Hydronic electric models cycle less and feel warmer at lower thermostat settings, trimming 10 to 15 percent off operating costs despite identical rated wattage. They cost roughly $100 more upfront and take 20 minutes longer to warm a cold room.

Safety and Code Considerations

Most jurisdictions require a permit and inspection for any new circuit serving a fixed heater. NEC 424.19 requires a disconnect in sight of the unit or a lockable breaker. In bathrooms, the heater must be at least 3 feet horizontally from the edge of a tub or shower unless explicitly rated for bathroom use.

Keep drapes, bedding, and furniture at least 12 inches from the grille face. Built-in tip-over and overheat sensors are now standard but should not be treated as insurance against blocking airflow.

When a Wall Heater Makes Financial Sense

Adding ductwork to an addition often costs $3,000 to $7,000. A pair of quality wall heaters, wiring, and thermostats total well under $1,000 installed. For rarely used rooms like guest bedrooms, workshops, or three-season sunrooms, the math strongly favors wall-mounted electric.

Skip this option if your electric utility rate exceeds $0.22 per kWh. At that point, a ductless mini-split pays back the price difference within 4 to 6 winters.

Common Installation Mistakes to Avoid

Five errors account for roughly 80 percent of the call-backs I see after a DIY install. Each is easy to prevent once you know about it.

1. Undersized wire — running 14/2 on a 2,000-watt 240V circuit when 12/2 is required pushes the wire past 80 percent of rated capacity
2. Stud bay too shallow — old 2×3 framing in walls built before 1950 will not accept a standard 4-inch deep can
3. Thermostat wired backwards — line and load terminals reversed means the heater runs full bore until the breaker trips
4. No high-temp cutoff — field-installed thermostats missing the fusible link violate NEC 424.20
5. Grille blocked by drapes — airflow restricted by 25 percent drops output by half and trips the overtemp switch constantly

Every one of these is a five-minute fix during install and a two-hour service call later.

Replacing an Old Wall Heater

Swapping out a 30-year-old Cadet for a modern equivalent is usually straightforward if the existing circuit is appropriately sized. The mounting can from the older unit often matches the replacement opening exactly, though many builders standardize on 14.5 by 12 inches now.

• Match voltage first — 120V replacement into a 240V can damages the new element instantly
• Inspect the wiring — aluminum branch wiring from the 1960s and 1970s needs anti-oxidant and AL-rated terminals
• Replace the thermostat — old bimetal stats drift 8 to 12 degrees; a modern electronic one costs $40 and holds within 1 degree
• Check the breaker — a 2-pole 20A breaker for 240V should show no heat discoloration at the bus

Budget $180 to $350 for a direct swap with like-for-like wattage. Upgrading to higher wattage usually requires pulling a permit and a bigger breaker.

When to Call an Electrician

Any new circuit, any aluminum wiring, any three-way tie into existing HVAC thermostats, or any unit in a damp location should route through a licensed electrician. Expect $200 to $600 for a dedicated new circuit in an accessible basement or crawlspace, and $500 to $1,200 if the run crosses finished walls. That is small money compared to a fire in a poorly grounded in wall heater install five winters from now.