Choosing a Heat Pump Installer in Sussex: Heat Loss, Emitters and the 2026 Grant Rules

If you are choosing a heat-pump installer in Sussex, compare the heating-system design they produce before you compare the badge on the outdoor unit or the grant-adjusted price.

Start with the heating design, not the badge on the outdoor unit. A credible heat-pump proposal should explain room-by-room heat loss, emitter output, hot water and operating temperatures before grant discounts are used to sell it.

A heat pump works as part of a system: heat loss, radiators or underfloor heating, pipework, hot water, controls and outdoor-unit location all affect performance.

Start with heat loss

Ask whether the proposal is based on a room-by-room heat-loss calculation.

That should inform:

• system output;
• flow temperature;
• radiator sizes;
• pipework;
• hot-water strategy.

A replacement based only on the old boiler's kW rating is not the same as a heat-pump design.

Lower-temperature heating changes emitter sizing

Heat pumps commonly work best with lower water temperatures than traditional boilers.

Ask what design flow temperature the installer is using.

Then ask which rooms need:

• existing radiator retained;
• larger radiator;
• different emitter;
• underfloor heating.

Do not accept “all radiators must change” or “none need changing” without the heat-loss/emitter calculation behind it.

Hot water needs its own design

If the property has a cylinder, ask:

• whether it is suitable;
• cylinder size;
• recovery;
• immersion;
• controls.

If there is no cylinder, understand what new storage/equipment is required and where it will go.

A combi-boiler home can require more internal changes than expected.

Outdoor-unit position affects noise and maintenance

Discuss:

• distance from bedrooms/neighbours;
• airflow;
• access;
• defrost water;
• pipe run;
• visual impact.

A unit should not be boxed tightly into a visually convenient corner.

Ask how it will be serviced later.

Planning rules changed in 2025

The government's 2026 Warm Homes Plan notes that England's permitted-development rights for air-source heat pumps were relaxed in May 2025.

Changes included removing the previous 1-metre boundary restriction in relevant cases and increasing some size allowances, among other updates.

That does not mean every installation is automatically permitted development.

Check the current conditions for your exact property and proposed equipment, particularly for protected/listed properties or unusual siting.

MCS matters for the Boiler Upgrade Scheme

Current GOV.UK guidance tells homeowners using the Boiler Upgrade Scheme to get quotes from suitable MCS-certified installers.

The installer applies for the grant on your behalf, and Ofgem contacts you to confirm.

If a quote assumes BUS funding, ask:

• current grant category;
• your eligibility;
• installer MCS status;
• what happens if the grant is not approved.

Do not compare a grant-discounted figure with a non-grant quote without separating the subsidy.

The 2026 grant rules changed

GOV.UK's current grant notice took effect on 21 July 2026. As checked on 19 September 2026, the main homeowner figures are:

• £7,500 towards an air-to-water heat pump;
• £7,500 towards a ground-source heat pump;
• £2,500 towards an air-to-air heat pump;
• an additional £1,500 until March 2027 for eligible properties heated by oil or LPG with no mains-gas connection, taking qualifying air-to-water or ground-source support to £9,000.

The detailed approved-grant notice separates categories by technology, fuel and grid status, so a headline figure is not enough to establish eligibility.

If a quote assumes BUS funding, make the installer show the grant category and amount on the quotation. GOV.UK says suitable MCS-certified installers apply on the property owner's behalf and Ofgem then contacts the owner to confirm.

Because scheme rules can change, verify the live GOV.UK position again before signing rather than relying on an old advert or screenshot.

Fabric upgrades can change the design

Tell the installer about planned:

• loft insulation;
• wall insulation;
• windows;
• extensions.

A heat-loss design based on the current house may be oversized after major fabric work.

Where sensible, coordinate energy improvements before the final heat-pump design.

Pipework can be the hidden constraint

Existing heating pipes may or may not suit the required flow.

Ask whether the survey includes:

• pipe sizes;
• circulation;
• zones;
• radiator valves;
• balancing.

Do not assume the outdoor unit can simply connect to every existing system unchanged.

Controls should be simple enough to use

Ask the installer to demonstrate:

• target temperatures;
• weather compensation if used;
• schedules;
• hot-water settings;
• backup/immersion;
• app/control ownership.

Heat pumps should generally be operated differently from short boiler bursts.

Handover matters.

Heat pumps in rented homes need usable handover

Store:

• design heat loss;
• emitter schedule;
• commissioning;
• MCS paperwork;
• grant records;
• model numbers;
• warranty;
• controls guide.

Tenants need simple operating instructions.

A poorly understood control strategy can create complaints even when the system is functioning correctly.

Compare quotes on the whole system

A useful quote should identify:

• heat-loss design;
• heat pump model;
• cylinder;
• radiators/emitters;
• pipework;
• electrical work;
• outdoor base;
• condensate/defrost drainage;
• controls;
• MCS/grant route;
• planning assumption;
• commissioning;
• warranty.

The lowest outdoor-unit price is not necessarily the lowest complete installation.

Ask for a system design, not just a unit price

You can browse heat-pump installers across Sussex or post the project.

A useful brief might say:

“Detached 1980s house in Eastbourne, currently gas combi with panel radiators. Loft insulation upgraded, no cylinder. Interested in air-to-water heat pump using current 2026 grant if eligible. Need heat-loss survey, radiator assessment and outdoor-unit options.”

That asks for a design, not a box.

The heat-pump quote should answer these questions

Confirm:

• heat-loss calculation;
• flow temperature;
• emitters;
• hot water;
• outdoor unit;
• pipework;
• controls;
• MCS;
• current grant assumptions;
• planning;
• commissioning.

The best heat-pump quote explains how the whole home will heat, not just which unit will sit outside.

That gives you a better basis for choosing an installer than comparing outdoor units without understanding how the whole home is expected to heat.