Vertical or horizontal radiators: which heats a room better?

Heat output is what matters, not the shape

Radiator output is published in watts, and in the UK usually at a standard test condition called ΔT50. That figure is what tells you whether a radiator will heat a room. A 1,200 W vertical radiator and a 1,200 W horizontal radiator put the same amount of heat into the room when the water in them is at the same temperature.

Where people get caught out is comparing a tall designer radiator by its size. Many vertical models are single panels or slim tubes, so a radiator that looks large on the wall can have a lower output than a modest double convector under the window. Always compare the watt figure at the same ΔT, not the dimensions. Our guide to the types of radiators compares panel, column, aluminium and cast iron models.

Our guide to choosing radiator size and heat output explains how to work out what a room needs. Do that before choosing the style, not after.

Where each type works best

In most living rooms and bedrooms with a window, a horizontal radiator under the glass is still the practical choice. Vertical radiators come into their own where there is no clear wall at low level, or where furniture needs the wall space that a long radiator would take.

Do vertical radiators heat the room unevenly?

Warm air rises from any radiator, and a tall one starts that rising air higher up, so it can feel as though more heat collects near the ceiling. In a room with a normal ceiling height and a properly sized radiator, the difference is small. The room reaches the same temperature, as long as the output is right.

The bigger effect comes from position. A radiator on an inside wall far from the window leaves cold air sliding down the glass and across the floor, and the room can feel draughty even when the thermostat is satisfied. If the only place for a vertical radiator is away from the window, consider a slightly higher output or better glazing and draught-proofing to make up for it.

Low-temperature systems and heat pumps

If your boiler runs at a lower flow temperature, or you are planning a heat pump, radiators give out less heat than their ΔT50 rating. At the lower temperatures heat pumps use, a radiator can deliver roughly half its rated output or less, so both vertical and horizontal radiators need to be larger to heat the same room.

That tends to favour horizontal double or triple panel radiators, which pack more surface area into the space under a window. A vertical radiator that is just about adequate at ΔT50 may fall well short on a heat pump. Our guides to a lower boiler flow temperature and to heat pump cylinder compatibility cover the wider system questions.

What changing from horizontal to vertical involves

Swapping like for like is the simplest radiator job there is, and our guide on how to replace a radiator walks through it. Changing orientation is closer to moving a radiator, and the price of the work reflects that. These are the things a plumber will look at:

• Where the flow and return pipes come up, and whether they can reach the new position, including under solid floors
• The valve connection type on the new radiator, which may be bottom, side or central
• The wall construction, and whether it will carry a tall, heavy radiator full of water
• Whether the system needs draining down and refilling with inhibitor, and the state of the existing water
• Whether the room's heat requirement is actually met by the chosen model

Moving a radiator on a sealed system or a system with microbore pipework takes planning. Our guides to moving or adding a radiator and to microbore pipes explain the extra steps.

Getting radiators replaced or repositioned

Loyal Plumbers replaces and repositions radiators across London and everywhere inside the M25, from straight swaps to moving a radiator to a new wall. We check the heat output the room needs, the pipework route and the wall fixing before recommending a style, so the radiator you choose actually keeps the room warm.

Call us or send an enquiry with the room, the current radiator size and where you would like the new one to go. If an existing radiator is cold or leaking rather than in the wrong place, our radiator repair and replacement service is the place to start.