Choosing and Positioning Radiators

Aluminium, bimetal, steel panel and cast iron radiators compared, why they go under windows, connection options and how to fit them into the interior.

Radiators are often remembered at the last minute in a renovation: walls are painted, curtains chosen, and then it turns out the old radiator does not suit the new interior or is in the wrong place. Yet radiator type and position affect both thermal comfort and the furniture and curtain plan. They should be planned together with the electrics and plumbing, before the rough-in work.

Radiator types

Four main types are found on the market:

• Aluminium radiators are light, heat up quickly and transfer heat well. They are sensitive to water quality, though; in central systems with aggressive water or fluctuating pressure, check the manufacturer's conditions before using them.
• Bimetal radiators combine a steel or copper core with an aluminium body. They withstand high pressure and are often chosen for central heating in apartment buildings.
• Steel panel radiators are flat and plain-looking, and common in systems with an individual boiler. They come in many heights and lengths but can be sensitive to water hammer and high pressure.
• Cast iron radiators are heavy, heat up and cool down slowly and last a long time. Decorative models are used as a feature in classic interiors.

The key selection criterion is the heating system itself: an individual boiler or the building's central system. Every radiator's data sheet lists its working and test pressure, and these must suit the system.

Sizing the output

Radiator size should not be chosen by eye. The heat output required depends on floor area, ceiling height, the number and size of windows, wall insulation and the room's position in the building, such as a corner room or top floor. This calculation should be made by a heating engineer or an experienced installer.

An undersized radiator leaves a room cold in winter, while an oversized one can upset system balance and add pipe and water volume for no benefit. Fitting identical radiators in every room of a flat is another common mistake: a north-facing corner bedroom and a hallway do not need the same amount of heat.

The output stated on the data sheet applies to a specific water temperature. If the system runs cooler, for example with a condensing boiler or heat pump, the radiator's real output drops, and this must be allowed for when sizing.

Why under the window

The traditional place for a radiator is under the window, and there is a physical reason. The window is the coldest surface in a room; cold air sinks beside it and spreads along the floor. Warm air rising from the radiator meets that downdraught, reduces condensation on the glass and evens out the room temperature.

General recommendations for the best result:

• the radiator should cover a good part of the window width;
• keep clearance from the floor and the window sill so air can circulate freely;
• leave a gap between the wall and the radiator;
• a deep window sill should not completely cover the top of the radiator.

Exact clearances are given in the manufacturer's installation instructions.

Connection layouts

A radiator can be connected from the side, diagonally or from below. A diagonal connection, with hot water entering at the top on one side and leaving at the bottom on the other, spreads heat evenly across long radiators. A bottom connection allows pipes to be concealed in the floor and looks tidier in modern interiors, but needs a suitable model or a dedicated valve set.

Each radiator should have isolating valves and an air vent. Isolating valves let you remove a radiator without draining the whole system, and thermostatic heads allow each room's temperature to be set separately.

Radiators in the interior

Hiding a radiator completely behind a decorative cover or deep boxing wastes a large share of its heat. If a cover is needed, choose one open at the front and top so air can pass. Heavy floor-length curtains drawn over a radiator trap warm air between the fabric and the glass.

For panoramic windows, low floor-standing radiators or trench convectors set into the floor are an alternative. In bathrooms, a heated towel rail acts as both heater and practical fixture. All these decisions belong in the design project, alongside the furniture and curtain plan.

In its design projects Zaferoğlu İnşaat positions heating emitters together with furniture, curtain and lighting decisions, and the company's curtain division helps with textile choices. Tell us whether the home runs on its own boiler or central heating, because radiator choice starts there.