Commercial air source heat pumps

How a commercial air-source heat pump is sized

An air-source heat pump takes heat from outside air and delivers it to your heating water. The output you need is set by the building’s design heat load: the heat it loses on a very cold day, worked out from the fabric, ventilation rate and operating pattern. It is not set by floor area, and it is not set by the size of the boiler you are replacing, which is often oversized.

Annual demand matters as well as the peak. A warehouse with high ventilation losses and a small office with long occupied hours can have the same peak and very different yearly energy use, and that changes both the running cost and the best plant arrangement. Ask any designer to show the peak load in kW and how it was calculated. If a quote simply matches the old boiler’s rating, ask why.

For rough orientation on price, one published installer guide gives planning bands for air-source systems of 100 kW thermal and above; the cost guide sets them out and explains how far to trust them.

SCOP, flow temperature and why they matter

The seasonal coefficient of performance (SCOP) is the heat delivered over a year divided by the electricity used. Rated seasonal figures are quoted to BS EN 14825, and they apply to the conditions stated, usually a particular flow temperature and climate. A headline COP measured at a mild air temperature is not a seasonal figure.

The main lever you control is flow temperature. The lower the water temperature a heat pump has to produce, the less work the compressor does and the higher the SCOP. That is why the existing emitters matter. Radiators, fan coils or air handling coils sized for hot gas-boiler water may need upgrading, or the design may accept a higher flow temperature and a lower SCOP. Domestic hot water raises the same issue: heating water to storage temperatures is a harder duty than space heating, and it may need a separate cylinder arrangement or a different unit.

SCOP also drives the running-cost result. The running-cost calculator shows the break-even SCOP for your own gas and electricity prices, which is worth checking before you assume any saving.

If your site has land or a borehole option, it is worth setting the two technologies side by side before you commit: the air source vs ground source heat pump comparison works through efficiency, space, planning and funding for commercial buildings.

Cascades, buffers and controls

Large loads are usually met by several modular heat pumps working together, called a cascade. The controller brings units on and off as demand changes. A cascade has practical advantages: each unit can run closer to its efficient part-load range, one unit can be serviced or fail without losing all heating, and the plant can be extended later.

• Buffer volume. A buffer vessel stops units short-cycling when demand is low and provides a defrost reserve. Undersized buffering can cause short-cycling and poor performance.
• Defrost. In cold, damp conditions the outdoor coil frosts and the unit periodically reverses to clear it. Ask how the design handles this and where the energy comes from.
• Controls and metering. Heat meters and electricity sub-metering let you measure the SCOP the system actually achieves, rather than relying on the rated figure.
• Retained boiler. Some sites keep a boiler for the coldest days; see hybrid and boiler-replacement retrofit.

Air-to-water systems and large buildings

Commercial units are almost always air-to-water: they move heat from outside air into a water circuit that feeds radiators, fan coils, air handling coils and hot-water storage. In a large building the water circuit is the part that decides the outcome, because the existing pipework, emitters and control zones set the flow temperature the heat pump must reach.

Large loads are usually built up from several modules rather than one machine. The cascade and modular systems guide explains how units share the load, and the flow temperature and emitters guide explains which emitters limit efficiency in an older building.

Planning permission for a commercial air source heat pump

The short answer: do not assume you have a right to proceed. Permitted-development rights for air-source heat pumps (Part 14, Class G of the General Permitted Development Order in England) cover dwellinghouses and blocks of flats. Commercial premises go to the local planning authority, which commonly asks for a noise assessment to BS 4142. Ask the authority early, and read the noise and planning guide before you fix a plant position.

The most efficient way to heat a commercial building

There is no single answer, because it depends on the building’s heat load, the flow temperature its emitters need, and the energy prices you pay. A heat pump delivers more units of heat than the electricity it uses, which direct electric heating cannot, and its efficiency is higher when it runs at lower flow temperatures. Whether it is also the cheapest to run depends on your tariffs against gas. The most efficient way to heat a commercial building guide works through the options.

Siting, noise and planning

Outdoor units need free airflow, space for service access and a position away from sensitive neighbours. Typical locations are flat roofs, ground-level compounds and yards. Each has cost implications: a roof position needs a structural check and a crane lift, and a compound may need fencing and acoustic screening.

On planning, be careful with what you read online. The permitted-development rights for air-source heat pumps (Schedule 2, Part 14, Class G of the General Permitted Development Order in England, as amended by S.I. 2025/560, with an MCS 020 noise limit of 37.0 dB(A) at the neighbouring habitable-room position) apply to dwellinghouses and blocks of flats. They are not a general right for commercial premises. For a business building, check with the local planning authority before design is fixed. A noise assessment to BS 4142, which compares the plant’s sound with the existing background level at the nearest sensitive receptor, is commonly requested. Listed buildings and conservation areas add their own requirements.

This site cannot tell you whether your plant needs consent; the planning authority can, and getting its view early avoids redesign.

Electrical supply and the grid connection

A heat pump replaces fuel with electricity, so the site’s electrical load rises. Check three things early. First, the capacity of your existing supply and main switchgear against the heat pump’s starting and running current. Second, whether the local distribution network operator (DNO) needs to reinforce the connection. Third, the cost and lead time of any upgrade, which sits outside the heat pump quote and which no one can state without asking.

Heat pump demand goes through the DNO’s connection process; the G99 process is for generation, not for heat pumps. Your DNO depends on where the site is: UK Power Networks covers London, the South East and the East; Electricity North West the North West; Northern Powergrid Yorkshire and the North East; National Grid Electricity Distribution the Midlands, South West and South Wales; SSEN and SP Energy Networks Scotland; and NIE Networks Northern Ireland. Your installer or an independent connections provider can make the application, but raise it before you commit to a design.

Funding: where the Boiler Upgrade Scheme does and does not reach

GOV.UK says the Boiler Upgrade Scheme grant can replace a heating system in a building used for your business. In England and Wales the installed heat pump capacity must be 45 kW thermal or less for a single heat pump (70 kW thermal for a multi-unit system), the building must be replacing a fossil-fuel or direct-electric system, and the application is made by an MCS-certified installer on the owner’s behalf. The grant is £7,500 for an air-to-water heat pump. That makes it relevant for small units such as shops, small offices and surgeries. Most medium and large commercial plant is above 45 kW thermal and falls outside it. The grants and funding guide covers what has closed and how capital allowances work. Heating plant is special-rate expenditure, so confirm the treatment with your accountant.