Castrads Mercury radiator in bronze

Heating a bay window: advice from our expert team

Written by
Nick Duggan

Bay windows are one of the most distinctive features in British homes. They bring in light, add character, and create a natural focal point in a room. They also come with plenty of questions when it comes to heating. We’ve answered the most common ones below.

Tuba classic steel bay window radiator in RAL 9016

Where should I position a radiator in a bay window?

In a conservation area or listed property, single-glazed windows and single-skin brickwork mean the building doesn’t benefit from the same insulation as a newer home. The most effective position for a radiator is directly beneath the glass, against the exterior wall. This placement tackles the area where heat loss is greatest, creating a warm curtain of air that counteracts cold coming off the glazing or draughts coming through the framework.

For homes where windows have been upgraded to double or triple glazing, or where additional insulation has been added, the rules become more flexible. “You don’t have to put the radiator in the bay itself,” says Nick Duggan, Managing Director at The Radiator Centre. “But positioning it there still makes practical sense. You’re heating the coldest part of the room first, and it keeps the bay feeling warm and usable rather than somewhere you avoid in winter.”

Nick adds: “Remember, just because you have a bay window, you don’t have to concentrate all of your heating there. You might choose to have one radiator in the bay and another elsewhere in the room.”

What heat output do I need for a bay window radiator?

Bay windows increase the exposed exterior surface of a room, which affects how much heat output your radiator needs to maintain a comfortable temperature. As a starting point, calculate the BTU requirement for the full room including the bay, rather than treating it as a separate space. The size and glazing type of the bay windows will influence this, as will the age and insulation of the property. Our BTU calculator takes into consideration the dimensions, external walls and type of glazing to help you.

If you’re doing significant alterations to the room, feel free to come in with your architectural plans and we can work out your calculations and give advice on heat output needs and radiator options. For a bay, you’ll also need to consider the proportions of the radiator, and may require a deeper radiator to meet both heat and proportion requirements. Mixing the depth and size of radiators across a room is often the most practical way to get the heat balance right without compromising on how the space looks.

Unlike most online retailers, we can make any radiator to order. You’re not limited to off-the-shelf dimensions that almost fit. The radiator is built to your exact dimensions, for both heat output and proportion.

“We always work out the heat loss calculation for the whole room before recommending a radiator,” Nick says. “Getting the output right is the priority, but with the right advice and the ability to make radiators to order, there’s no reason you can’t achieve both.”

What style of radiator works best in a bay window?

Steel column radiators are the most popular choice for bay windows because they work across both traditional and contemporary interiors. They are also lighter than cast iron, which is worth bearing in mind if the radiator needs to be carried up multiple flights of stairs.

Cast iron offers a different quality of warmth to steel. It takes longer to heat up but retains heat for longer, continuing to warm a room even after the heating has switched off. Cast iron radiators are a strong option in period properties, particularly Victorian and Edwardian homes where the radiator is meant to feel like part of the original architecture. Our Castrads range is still an independent radiator maker owned by the same family for generations and made in North West England, combining traditional casting methods and designs. The casting process gives the finished radiator a distinctive, patinaed quality that feels quite different from steel, and sits particularly well in period interiors. Once in a property it feels like it has been there a lifetime.

For box bay windows where the angle of the exterior wall is less pronounced, or where a door leads out from the bay, slimline low-level panel or horizontal designs can work well without interrupting sightlines or impeding the doorway.

Nick puts it well: “The bay window is one of the few places in a room where the radiator naturally becomes a feature. Customers are often more willing to make a statement here than anywhere else in the house, whether that’s through colour, finish or an unusual design.”

Emmeline III 470 Cast Iron radiator Little Greene Affogato in bay window

Can I get a radiator made to fit my bay window exactly?

Yes. Any radiator we sell, straight, curved and angled, can be custom made to match the specific dimensions of a bay window, including bespoke angles for non-standard spaces. This is particularly relevant in older properties, where bays rarely conform to standard measurements.

“No two Victorian or Edwardian bay windows are ever exactly the same, even if they look it at a glance,” says Nick. “We can provide exact specifications including pipe centres before you order, so you can see precisely how the radiator will sit in the space before committing, and your plumber will have the information required for his quote and first fit. It removes the guesswork and means the finished result looks intentional rather than like something that almost fits.”

If you have more than one room where you’re replacing radiators, we offer a home visiting service. We can take measurements and give advice as we move from room to room, often giving customers ideas they hadn’t considered, or a useful list of questions to take back to their plumber.

Find the right radiator for your bay window

Every bay window is a little different, so getting the fit right matters as much as getting the heat output right. Our team can talk you through positioning, style and made-to-order sizing, or come to you and take measurements so you know exactly how a radiator will sit before you commit to anything.

Visit a showroom to explore finishes and shapes in person, or get in touch to talk through your bay window with our team.

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