Replace Electric Radiators with a Caldo Optima Heat Pump on the Wirral: The 5-Hour Retrofit That Halved One Family’s Bill

06:30: “Dad, the radiator’s cold again”

It’s Boxing Day, 3 °C outside, and the Fischer “dynamic” electric radiator in the living room has been off-peak since 23:00. By breakfast the bricks are stone-cold, the thermostat reads 17 °C, and the Lewises are wearing coats indoors. Again.

Electric radiators are marketed as “100% efficient”. Trouble is, 100% of 28 p/kWh (Octopus Flexible, January 2026) is still 28p, three times the cost of gas and, as we’ll show, twice the cost of a Caldo Optima heat pump running on the same tariff.

What the Internet Won’t Tell You About Electric Radiators

• Fischer, Trust, Best Heating “German dry-stone” units draw full rated power: 1.8 kW in, 1.8 kW out. No magic.

• No modulation: on or off, like a 1972 kettle.

• Need a dedicated 32 A radial for every room in many Wirral 1960s semis consumer panel Tetris that adds £650 to install.

• Elements degrade: Fischer quotes £110 per rad to replace after 8 years.

A heat pump, by contrast, moves heat, not makes it. The Caldo Optima 12 delivers 3.5 kW of heating for 815 W input. A real-world COP of 3.6 on the Wirral coast (average winter 7 °C ambient, 80 % RH).

Meet the Caldo Optima 12 – Specs That Fit a Wirral Terrace

No outdoor unit frost nightmares: Caldo’s DC-inverter compressor ramps from 18 Hz to 90 Hz in 4 seconds, keeping evaporator temp above -12 °C. That means no supplementary heater needed even when the Mersey fog drops to -2 °C.

The 5-Hour Retrofit: Step-by-Step in Heswall

We filmed every minute, here’s the director’s cut.

Hour 0 – Survey (already done)

• Heat-loss calculation: 3.2 kW @ 21 °C, 2.4 air changes/hr.

• Radiator count: 8 Fischer units totalling 12.8 kW—oversized by 300 % because they cycle off when bricks cool.

Hour 1 – Strip-Out

• Isolate circuits, remove rad brackets, polyfilla two 10 mm holes.

• Disconnect 8 × 32 A rad radials. Consumer panel suddenly has breathing space.

Hour 1.5 – Mount & Pipe

• Hang Caldo on vibration-isolating rail; only two fixings hit brick, rest into studs, no steels needed.

• Core 152 mm hole for refrigerant lines & condensate to outside. Wirral sandstone cuts in 7 minutes with diamond core.

Hour 2 – Vacuum & Commission

• Pull 200 micron vacuum for 20 min (R290 is flammable—no shortcuts).

• Pressure-test to 3.8 MPa, leak-test with electronic H2 detector.

Hour 2 – Electrics & Controls

• 13 A fused spur from original radial; Wi-Fi stat paired; MCS paperwork photographed and uploaded.

Hour 2.5 – Handover & Tea

• Show Mr Lewis the app: schedules, COP dashboard, “holiday mode” that drops to 15 °C and saves 25 %.

• Brew, custard cream, done, 2 hours and 16 minutes total.

5. The Numbers: Before vs After

Comfort side-effect: mean living-room temp rose from 18.5 °C to 21.2 °C because the heat pump runs continuously at part-load instead of blasting 2 kW then switching off.

Noise Check: Will My Neighbours Hear It?

Caldo on silence mode: 39 dB(A) at 1 m, equivalent to a library. Fischer’s own data sheet lists 44 dB(A) for their “silent” rad. Recorded from next door’s bedroom: 28 dB(A), below ambient wind. Planning permission not required for permitted development rights on the Wirral.

Maintenance & Lifespan

• No replacement elements: Caldo uses inverter-driven rotary compressor rated for 30 000 h = ~20 years at 1 500 h/yr.

• Annual check: rinse coil, verify condensate, £79 service plan.

• Warranty: 10 years parts & labour if serviced by Caldo-authorised partner (that’s us).

Grants & Payback

• Boiler Upgrade Scheme: £2,500 off upfront (MCS install mandatory).

• No VAT on labour until March 2027 - saves further £350.

• Net cost to customer after grant: typically £3,700.

• Simple payback: £3,700 ÷ £490 annual saving = 7.5 years.

• Added house value: A 2025 RICS study puts ASHP premium at 1.8 % - £4,800 on an average £265k Wirral semi. You’re cash-positive on day one.

Wirral-Specific FAQ

Q: Will the sea air corrode the coil?
A: Caldo uses blue-fin hydrophilic epoxy coating—1 000 h salt-spray tested (ASTM B117). Southport promenade units still pristine after 4 years.

Q: Do I need planning permission in a conservation area?
A: No. Permitted development class covers air-to-air <0.6 m³ volume. For listed buildings we supply acoustic housing (adds 2 dB).

Q: Can it cool in summer too?
A: Yes, Caldo Optima is reversible (EER 2.6). One remote click and your living room becomes a 3.5 kW air-conditioner during the two days Merseyside hits 28 °C.

Book a Survey, Get a £150 Wirral Welcome Credit

We have six survey slots left this week covering all of the Wirral. Fill the 30-second form, we’ll laser-measure every room, email you a COP-vs-tariff graph and, if you book before 31 January, knock £150 off the install.

REQUEST A SURVEY NOW