Short definition
A panel radiator is a pressed-steel hydronic emitter — typically two welded sheet-steel panels with internal water channels, mounted vertically on a wall. Available as single panel, double panel (with rear convector fins), or double-panel-double-convector for higher output per face area. Standard test rating per EN 442 at 75°C flow / 65°C return / 20°C ambient.
What it is
A panel radiator does the same job as a cast-iron column radiator but with a fraction of the weight and water content. Two stamped sheet-steel panels are pressed with vertical water channels, welded along the edges, and connected to inlet and outlet pipes at the bottom or side. Hot water flows through the channels; the steel face radiates heat into the room; convector fins (on double-panel and double-double-panel models) accelerate heat transfer by warming air drawn up through fin gaps.
Naming convention you’ll see on spec sheets:
- Single panel (Type 11): one panel, no convector. Lowest output for a given size.
- Double panel (Type 22): two panels stacked front-to-back, both with rear convector fins. Roughly double the output of a single.
- Double-double-convector (Type 33): three panels with two convector banks. Highest output per wall length.
EN 442 is the European test standard the source book references; US-market panel radiators built to similar standards typically publish ratings at the 75/65/20 (ΔT 50) condition. Output drops sharply at lower supply temperatures — important for heat-pump compatibility, same logic as for baseboard.
The connection options on the radiator body — TBOE (top-bottom-opposite-end), BBOE (bottom-bottom-opposite-end), and others — affect output by 5–10% depending on flow distribution within the panels. A specifier picks the connection pattern based on plumbing layout.
Why it matters to a homeowner
Most homeowners interact with panel radiators in three ways.
Sizing during a remodel or addition. A new room or a room that “feels cold despite the radiator” needs a properly sized panel rad — output rated for the design-day heat loss of the room at the system’s actual supply temperature. A contractor who quotes “another double-panel like the one in the next room” without doing a heat-loss calculation is guessing. For new emitters, ask for the heat-loss calculation and the radiator’s manufacturer-published output at your system’s supply temp.
Heat-pump compatibility. Same issue as baseboard: panel radiators sized for 180°F boiler supply produce roughly half their rated output at 130°F (the typical heat-pump supply temperature). A heat-pump retrofit on a panel-radiator home often needs upsizing — same wall length, but Type 33 instead of Type 11, or a longer Type 22 instead of a shorter Type 33.
Maintenance. The same hydronic-system maintenance applies — bleed when air-locked, check for cold-spots that signal sludge, and confirm corrosion inhibitor concentration during annual service.
When you’ll encounter this term
- A boiler-swap or heat-pump retrofit quote sizing new emitters.
- A new room or addition with hydronic distribution.
- Replacing an old cast-iron radiator with a modern panel.
- A real-estate listing for a 1990s+ WA build with hydronic heat.
Common variants and disambiguation
- Panel vs. column radiator. Panel = pressed-steel slab. Column = decorative cast-iron with multiple parallel sections. Cast-iron columns hold dramatically more water and have higher thermal mass; panel rads respond faster.
- Panel vs. baseboard. Panel = vertical wall-mount slab. Baseboard = horizontal floor-edge fin-tube convector. Different installation, similar BTU/sq ft of wall area for double-panel rads.
- Single vs. double panel. Double-panel produces roughly twice the output for the same wall length.
Common failure modes
- Cold-spot in middle. Magnetite sludge in lower channels. Schedule a power flush and verify corrosion inhibitor.
- Cold at top, hot at bottom. Air trapped — bleed it.
- Pinhole leak. Long-term internal corrosion, usually from a system without inhibitor. Replace the radiator.
- Rust streak on the cover. Weeping joint at the top valve packing. Repack or replace the valve.