Upgrading Radiators for Heat Pump Compatibility in Your London Home
Installing a heat pump in a London home that currently has gas central heating often requires upgrading the radiators to work efficiently at lower flow temperatures. This guide explains how to assess your existing radiators, which sizes are needed, and what the upgrade process involves.
Why Existing Radiators May Not Work Efficiently with a Heat Pump
When a gas boiler system is replaced with an air source heat pump in a London home, the flow temperature of the heating system typically falls from 65 to 75 degrees Celsius to 40 to 50 degrees Celsius. Radiators are rated at a standard test condition of 75 degrees Celsius flow and 65 degrees Celsius return, producing a mean water temperature of 70 degrees Celsius and a temperature difference between the water and a 20 degree Celsius room of 50 Kelvin. This is the DT50 condition used for all published radiator output data.
When the same radiator is operated at 45 degrees Celsius flow and 40 degrees Celsius return, the mean water temperature is 42.5 degrees Celsius and the temperature difference from the room is only 22.5 Kelvin. The heat output of the radiator at this lower temperature is substantially less than the published DT50 figure. The exact correction factor depends on the type of radiator, but as a general guide, a radiator operating at DT20 delivers approximately 40 percent of its rated DT50 output. This means that a radiator rated at 1500 watts at DT50 delivers only about 600 watts at DT20.
Assessing Whether Your London Home Radiators Need Upgrading
A heat pump installer will carry out a heat loss calculation for each room in your London home as part of the design process. This calculation determines how many watts of heat output are required in each room to maintain the design temperature of 21 degrees Celsius when the outside temperature is at the design minimum, typically minus three degrees Celsius for London. The installer then checks whether the existing radiators in each room, when derated to the operating temperature of the heat pump system, can deliver the required output. Where they can, the existing radiators can be retained. Where they cannot, larger or additional radiators are required.
The outcome of this assessment varies considerably between London properties. A 1990s semi-detached house with large panel radiators that were generously sized originally may need few or no upgrades. A Victorian terrace where the radiators were already marginal at gas boiler temperatures will almost certainly need significant upgrades throughout. A bathroom with only a small towel rail will almost always require a larger towel rail or a supplementary electric heating element within the towel rail to provide adequate output at heat pump temperatures.
The Radiator Upgrade Process for Heat Pump Installation in London
Radiator upgrades for heat pump installation typically involve replacing existing single or double panel radiators with larger double panel double convector radiators on the same pipework connections. In most cases, the existing flow and return pipework connections can be reused with minimal modification, as modern panel radiators are available in a wide range of sizes and can usually be found in dimensions that fit within the available wall space. In some rooms, where the wall space does not accommodate a larger radiator, a vertical radiator or a column radiator with a higher output per unit of width may be substituted.
The physical installation process involves draining the section of the heating circuit connected to the radiator being replaced, removing the old radiator and its valve tails, fitting new valve tails to the replacement radiator, hanging the new radiator on its brackets, and reconnecting the valves. On a whole-house radiator upgrade in a London property, a competent heating engineer can typically replace six to eight radiators per day. The system is then refilled, bled, and pressure tested before the heat pump is commissioned. Prestige Engineers carry out radiator surveys and upgrades throughout London as part of heat pump installation projects, ensuring that the heating system is properly designed to maximise heat pump efficiency from day one.