Planning a Whole-House Energy Retrofit: Where to Start

What “whole-house” actually means

It does not mean you must do everything in one month. It means you treat the home as one energy system:

• •How heat escapes (fabric and air leakage)
• •How heat is supplied (plant and emitters)
• •How electricity is used and generated
• •How moisture is managed when you tighten the envelope
• •How you control and pay for energy day to day

Start the sequence with diagnosis, not a product quote — see also low carbon home energy.

Why order matters more than brand

A large heat pump on a leaky solid-wall cottage fights the building every cold night. Solar on a roof while the loft is uninsulated offsets electricity you need not have used. A battery sold as “winter independence” does not rewrite South West January irradiance.

Good order reduces the size of plant you need, improves comfort, and makes grants and payback claims more honest. Bad order spends capital twice — once on oversized kit, again on the fabric work you should have done first.

Step 1 — Survey the building (as it is)

Walk the house with a critical eye before you invite three technology quotes.

For heat-pump readiness questions, use the heat pump readiness checklist; for floors, the UFH renovation checklist.

Step 2 — Heat loss before plant size

Design outdoor temperature matters in the South West as well as up north — coastal vs inland/upland. See heat pumps in cold weather and what size heat pump do I need?.

A proper heat loss calculation estimates how much heat each room needs on a cold design day. That number drives heat pump capacity and whether radiators or underfloor heating can deliver comfort at a low flow temperature.

Rule-of-thumb “11 kW for a 3-bed” is not a design. Neither is an EPC alone.

In the South West, outdoor design temperatures are often milder than northern UK references (Plymouth-class figures around −1.5°C appear in published design data) — but inland, upland and Dartmoor-edge sites are not seafront plots. Ask what weather location was used.

Deep dive: what is a heat loss calculation · what size heat pump · cold weather performance.

Step 3 — Fabric improvements that usually pay

Not every measure is equal. Prioritise by cost, disruption and heat-loss impact for your construction.

Solid stone and cob need moisture-aware detailing. “Seal everything” without a ventilation plan is a mould strategy, not a retrofit strategy. See condensation and mould.

If fabric works are definitely happening in the same programme, the heat loss can reflect the improved building. If they are “someday,” size heating for the house you actually have.

Step 4 — Ventilation when you tighten the house

Older South West homes often leak air. That wastes heat — and also dilutes moisture from cooking, showers and indoor drying. Improve airtightness without extract and humidity has nowhere to go.

Minimum practical package for many homes:

• •Working extract to outside in kitchens and bathrooms
• •Trickle vents used, not permanently closed
• •A drying strategy that is not “radiators in every bedroom all winter”

Whole-house MVHR can make sense on deeper airtightness projects. It is not automatic with every heat pump. Proportionate beats fashionable.

Step 5 — Low-temperature heating design

With heat loss in hand, design the heat source and emitters as one system.

Heat pump

Size from design outdoor temperature and capacity tables — not brochure kW at mild conditions. BUS grant: typically £7,500, or £9,000 for many oil/LPG replacements with no mains gas (confirm GOV.UK). Rural Devon and Cornwall switchers often sit in that second story.

Also: flow temperature, heat pump + UFH worth it?, heat pump noise. Guides: costs 2026 · running costs · vs gas/oil · grants.

Emitters — radiators or underfloor

Low flow temperatures need enough emitter surface. That may mean larger radiators, fan-assisted emitters, or underfloor heating designed for the room loss.

UFH is not mandatory. It is often ideal with heat pumps when the floor build-up allows — especially renovations using overlay on solid floors and joist systems upstairs.

UFH costs: UFH costs 2026. UFH cluster: renovations · overlay vs screed · systems explained · radiator upgrades.

Hot water

Cylinder size, coil rating and controls matter. A heat pump domestic hot water setup is not a straight swap of a combi mindset — plan storage and recovery honestly.

Step 6 — Solar and storage (after the load is understood)

Once heating and fabric direction are clear, size PV to residual electricity use and roof reality. Add a battery only if self-use and tariffs justify the capital.

Winter gap remains: heat demand peaks when solar is weakest. Solar improves the annual bill; it does not make January free.

Checklist: solar & heat pump planning checklist. Guides: solar before or after HP · payback · battery worth it? · combined stack.

Step 7 — Controls, tariffs and how you live

The best hardware fails soft if operated like a 1990s gas boiler on deep setbacks.

• •Weather compensation commissioned for the emitters you have
• •Steady temperatures on UFH rather than big overnight dumps
• •A heat-pump or time-of-use tariff that matches how you use power
• •Hot water schedules that do not fight heating all evening

See running costs explained. From our running-cost work, tariff choice alone can move annual cost by roughly £150–£300 on typical homes versus a poor default rate — before solar is counted.

Phasing when you cannot do everything at once

Realistic multi-year paths for many SW households:

Urgent boiler failure collapses the timeline — heat first, then catch fabric and solar. Do not sit without heat waiting for a perfect masterplan.

Money, grants and expectations

Whole-house work is major capital even with support:

• •BUS on eligible heat pumps (£7,500 / £9,000 oil-LPG off-gas where rules allow)
• •Solar and batteries are separate investments
• •Fabric measures may attract other local or national help at times — always check current schemes

ECO4-style routes have been limited in practice for many Devon and Cornwall households — do not plan a retrofit that only works if a grant fairy appears. Independent framing: grants & schemes.

Comfort and lower carbon are valid goals alongside payback. Just keep the spreadsheets honest.

Devon & Cornwall-specific constraints

• •Solid stone and cob — moisture, breathability, and realistic U-values
• •Conservation areas and listed buildings — external insulation and windows may be constrained; floors and lofts are often freer
• •Off-gas rural heating — oil/LPG economics and higher BUS band where eligible
• •Damp winters and indoor drying — ventilation is not optional
• •Exposure — coastal wind and inland/upland cold snaps change design loads
• •Tourism / second homes / holiday lets — occupancy patterns change self-use and heating schedules

Older homes overview: heat pumps in older homes · carbon framing: low carbon home energy.

Who should be on the team

You do not need a dozen consultants. You do need clear ownership:

• •Someone accountable for heat loss and heating design (often the MCS heat pump installer — interrogate the method)
• •A competent electrical view for heat pump + PV + EV headroom
• •Building fabric advice that understands solid walls and moisture if you go deep on insulation
• •You — with bills, occupancy patterns and a written priority list

HeatWiseSW’s role is independent clarity first, then introductions to reputable local installers when you are ready — not a single forced product path.

Mistakes that waste years of capital

• •Heat pump sized from boiler badge or floor area folklore
• •Fabric ignored until after plant is in
• •Airtightness without extract
• •Solar sold as winter heat
• •Battery sold as off-grid
• •UFH without height survey or manifold commissioning
• •Three installers, no shared design numbers
• •Deep setbacks on high-mass floors then blaming the technology

Starter checklist you can print

Topic deep-dives: heat pump readiness, UFH renovation, solar + heat pump planning.

Honest bottom line

Frequently asked questions