If you want to know how to heat a sunroom, start with one fact: glass loses heat fast. The windows that make the room bright at noon pull warmth out of it at night and on cloudy days. The right heater depends on how you use the room, how much glass it has, and what wiring you already have. This guide compares the main options, gives you a sizing rule of thumb, and covers voltage, mounting and safety.
How to heat a sunroom: why glass rooms are hard
A sunroom flips the usual ratio of insulated wall to window: most of the wall area, and sometimes the roof, is glass. Even good double pane glass insulates far less than an insulated wall.
The U.S. Department of Energy’s Energy Saver guidance on sunspaces notes that sloped glazing collects more heat in winter but also loses more heat at night, and it calls glazed sidewalls “net heat losers.” A sunroom can feel warm on a sunny afternoon and cold an hour after sunset.
Three other things make it harder:
- No ductwork. Many sunrooms were added later and never tied into the main heating system.
- Tile or concrete floors feel cold and soak up heat.
- Air leaks around sliding doors, screen panels and roof joints.
That is why radiant spot heat often works better in a sunroom than trying to warm all the air.
Best heater for a sunroom: options compared
| Option | Best for | Power or install | Watch out for |
|---|---|---|---|
| Ductless mini split | Four season rooms used daily, heating and cooling | Installed by an HVAC contractor | Highest upfront cost |
| Wall or ceiling infrared panel | Seating areas in rooms with lots of glass | 120V plug in or 240V hardwired | Heats people and surfaces, not all the air |
| Electric fireplace | Ambiance plus supplemental heat | Plug in or hardwire, built in or freestanding | Modest heat output for a glass room |
| Portable space heater | Occasional use, small rooms | Standard 120V outlet | Cords, tip over risk, clearances |
| Extending ductwork | Rooms next to an existing duct run | HVAC contractor adds a supply run | One register may not keep up; can unbalance the house |
ENERGY STAR describes ductless mini splits as designed for spaces without ductwork, including additions where extending ducts is difficult, and notes that many certified models heat well even in very cold climates. If you use the room year round and want cooling too, get a quote. Otherwise, read on for the electric options we carry.
Infrared heater for a sunroom
Infrared panels warm people and objects in their path rather than the air between. In a glass room where warm air keeps escaping, you still feel warm in your chair.
The RADtec Design Series panels give off no orange glow, and the listings describe them as rated for indoor and covered outdoor use, useful in a damp three season room:
- Design Series 43 inch 1500W 110V: about 50 sq. ft. of indoor space.
- Design Series 47 inch 1500W 110V Indoor/Outdoor: about 50 sq. ft., IPX5 water resistance.
- Design Series 62 inch 2400W 220V: about 80 sq. ft.
- Design Series 82 inch 3200W 220V: about 110 sq. ft.
- Genesis Series 25 inch 1500W 110V: a lower cost medium wave option, about 50 sq. ft. indoors, IP65.
Those coverage numbers describe the zone a panel keeps comfortable, so a larger sunroom usually needs two or more panels aimed at where you sit. Heating a workshop instead? See our infrared garage heater guide.
Electric fireplace in a sunroom
An electric fireplace adds a focal point and a fan-forced heater, and the flames can run without heat in summer. The models below list about 4,800 BTU, roughly 1,400 watts, so treat them as supplemental heat in a glass room.
- Amantii Panorama Series 30 inch Extra Slim: recesses about 4 inches into a wall and is rated for indoor or covered outdoor use.
- Amantii Symmetry 42 inch: an indoor built in unit that plugs in or hardwires, for a four season room with an interior wall.
- Sierra Flame Lynwood E50: a cast iron freestanding electric stove described for home use, so keep it in a fully enclosed, dry sunroom.
Compare more models in our electric fireplace buying guide, or read electric fireplace vs space heater.
Patio heaters such as the Napoleon Phantom are described as outdoor heaters, so we would not use one in a sunroom. For an open porch or deck, start with our patio heater buying guide.
Sunroom heater size: a rule of thumb
Dimplex, a major electric heater maker, gives a general rule of 10 watts per square foot: a 1,000 watt heater warms about 100 sq. ft. in a standard insulated room. Dimplex recommends a heat loss calculator for an accurate figure.
A sunroom is not a standard insulated room, so plan for more than 10 watts per square foot, and more again for a glass roof, single pane windows or a cold climate.
- Multiply floor area by 10. A 12 by 14 foot room (168 sq. ft.) gives about 1,700 watts.
- Increase that for heavy glass or drafts. Many sunrooms need two heaters.
- For infrared panels, size by seating zone using each listing’s coverage figure.
How to heat a three season room: 120V vs 240V
Portable heaters and small infrared panels run on 120V. A 1,500 watt heater draws about 12.5 amps at 120 volts, most of a typical 15 amp circuit, so do not share that circuit with other heating appliances.
240V heaters such as the 2400W and 3200W panels put out more heat but need a dedicated circuit, usually hardwired by a licensed electrician. Dimplex advises checking local building codes before choosing a breaker size. For spring and fall use, one or two 120V units are often enough. For January, budget for 240V wiring or a mini split.
Mounting clearances and safety
Every wall or ceiling heater lists minimum clearances in its installation manual. Follow those exact numbers; Dimplex notes clearances are part of a heater’s CSA or UL approval. The RADtec Design Series brackets mount on a wall or ceiling with 90 degrees of adjustment, so you can angle a panel at seating.
From the Chicago Fire Department’s space heater safety tips:
- Keep all sides of a space heater at least 3 feet from curtains, sofas and anything that can burn.
- Never use an extension cord or power strip, and never run the cord under a rug.
- Plug only one heat producing appliance into a wall outlet at a time.
- Do not leave a heater running unattended or while you sleep.
Also look for a UL, ETL or CSA certification mark, and confirm the unit is rated for damp locations if needed.
Frequently asked questions
What is the best heater for a sunroom?
For daily, year round use, a ductless mini split. For seating areas in a glassy room, infrared panels. For ambiance, an electric fireplace as a second heat source.
What size heater do I need for my sunroom?
Start with about 10 watts per square foot, then go higher because glass loses heat faster. Large rooms often need two heaters.
Is an infrared heater good for a sunroom?
Usually, yes. It warms you directly even when air near the windows stays cool. Pick one rated for covered outdoor use if the room gets damp.
Can I put an electric fireplace in a three season room?
Yes, if the listing allows that location. The Amantii Panorama Extra Slim is rated for indoor or covered outdoor use.
Do I need an electrician to heat a sunroom?
Not for a 120V plug in heater on a suitable outlet. You do for 240V heaters, hardwired fireplaces and mini splits. Questions? Call 866-777-2590, Monday to Friday, 9AM to 6PM PST.
