Choosing a radiator for a flat: types and sizing

Panel radiator or bimetal — what the difference actually is

A panel radiator is a flat steel panel, sometimes with one or two extra panels and convector fins welded behind it to push out more heat. It is the standard choice in flats: light, inexpensive, quick to warm up and quick to cool down again once the heating drops. Most Estonian flats already have something similar, so a like-for-like swap is usually straightforward.

A bimetal or tubular radiator is built from separate sections, each with a steel core and an aluminium or cast-iron outer surface, bolted together to the width you need. They hold more water, take longer to heat up, and cost more per kilowatt of output. They suit rooms where you want steady, even heat rather than a fast response, and they are more common in houses with their own boiler than in panel-building flats.

For most flat renovations a panel radiator is the sensible default. Bimetal sections earn their price in a room with high ceilings or poor insulation, where steady output matters more than quick response, or where the look of individual sections is what you want.

How to work out the size you need

Radiator output is given in watts, and the rule of thumb used in Estonian housing is roughly 100 watts per square metre for a room with normal ceiling height and reasonable insulation, more for a corner room, a room with a large window, or a poorly insulated 1930s wooden house, less for a small, well-insulated room in a newer development. This gives you a starting figure, not a precise calculation.

Multiply the room's floor area by that figure to get a rough wattage, then check the manufacturer's output rating for the radiator length and height you are considering — it is printed on every product page and varies a surprising amount between otherwise similar-looking models. Buying slightly oversized is a safer mistake than buying undersized, because a radiator with a thermostatic valve simply runs cooler when it has more capacity than the room needs.

Height and length are also a practical question of what fits under the window and around the pipework already in the wall. Measure the gap, note where the existing pipes come up or out of the floor, and take that measurement with you rather than guessing from memory.

• Measure floor area and ceiling height of the room
• Add extra capacity for corner rooms, large windows or older wooden houses
• Check the manufacturer's stated output in watts, not just the physical size
• Measure the space under the window and the position of existing pipes
• When in doubt, size up slightly rather than down

Fitting a district-heated panel building

Most Tallinn panel buildings run on district heating with a shared riser system, and the flat's heating is part of the building's overall balance rather than an independent circuit. This matters for two reasons: the radiator's flow rate needs to suit the system pressure the building runs at, and any change to the pipework can affect how the rest of the stack balances.

Panel radiators with a built-in valve set are usually fine in this kind of system and are what most suppliers stock as the default for flats. If your building's korteriühistu has done a recent heating renewal or installed thermostatic valves throughout, check with them or with whoever manages the building's heating before buying, since some systems specify a particular valve type or connection standard.

This is also the point where it is worth having a plumber look at the existing pipework rather than assuming a straight swap. Older flats sometimes have corroded or undersized pipe stubs that are the real reason a room never warms up properly, and no amount of radiator shopping fixes that.

What to ignore in the marketing copy

Radiator packaging and shop websites talk about finishes, colours, designer panels and claimed efficiency ratings that are hard to verify and largely irrelevant to how warm your room gets. A radiator's job is to move enough hot water through enough surface area to match its stated wattage — everything else is styling.

Be sceptical of vague claims about heating a room faster or saving money without a stated wattage and a stated room size to back it up. The only numbers worth comparing are the physical dimensions, the rated output in watts, and the price. A plain white panel radiator from a reputable supplier heats a room exactly as well as an expensive designer version rated at the same output.

Once you have chosen a radiator, what happens next

Buying the radiator is the easy part; fitting it correctly is where a mis-sized valve, a leaking joint or a badly bled system causes problems later. We install radiators from 85 € per job, including connecting to the existing pipework and bleeding the system, and if there is broader pipework to sort out first, plumbing work is billed from 45 € per hour.

If you are not sure which size or type suits your room, a photo of the space and the existing radiator along with the room's dimensions is usually enough for us to advise before you buy, which is worth doing before spending money on the wrong unit.