For developers and heating engineers specifying a gas boiler replacement, the decision is rarely about which technology is "better". It is about which one fits the building. An air-source heat pump converts one unit of electricity into three or more units of heat, but only when it runs at flow temperatures of roughly 35ā50Ā°C. In a solid-walled Victorian terrace, that usually means larger emitters, new pipework and fabric upgrades before the COP advantage actually shows up. The Tepeo ZEB takes the opposite approach. It is resistive at 1:1, but it stores heat in a ceramic core and pushes 80Ā°C water through the radiators that are already there.
De-risking the "Heat Pump Horror Stories"
The internet is full of cautionary tales from homeowners complaining about cold rooms, noisy outdoor units, and skyrocketing electricity bills after switching to an air-source heat pump. From an engineering perspective, these failures are almost always issues of hydraulic design rather than hardware defects. Because heat pumps are low-flow systems, dropping them into a leaky property with undersized radiators forces the compressor to run at maximum capacity, destroying the Coefficient of Performance (COP) and generating acoustic hums. The Tepeo ZEB sidesteps this entire design risk; by matching legacy gas boiler temperatures out of the box, it completely eliminates the structural need for deep fabric retrofits or radiator overhauling.
Peak electrical load is where the two systems differ most. A heat pump draws a continuous, low-amperage current spread across the day, which sits comfortably within most single-phase supplies. The ZEB concentrates its demand into an intense 9kW, 40A charging spike. Without strict overnight scheduling on a tariff such as Octopus Intelligent Go, a 1:1 system bought at peak rates quickly becomes uneconomic. Smart tariff integration is what makes the ZEB financially viable, and it should be treated as part of the specification rather than an extra.
Homeowners often ask about summer shutdown. The ZEB's dry ceramic core has no water, refrigerant or compressor, so six months of warm-weather idleness causes no degradation. Meanwhile, a paired Mixergy cylinder takes over domestic hot water and handles summer solar diversion on its own, heating only the volume the household actually needs.
Air-Source Heat Pump vs. Tepeo ZEB + Mixergy
| Metric / Requirement | Air-Source Heat Pump (ASHP) | Tepeo ZEB + Mixergy Smart Cylinder |
|---|---|---|
| Thermodynamic Efficiency | 300%ā420% efficient (COP 3.0ā4.2) | 100% efficient (COP 1.0) |
| Operational Strategy | Continuous, low-temperature ambient heat extraction | Off-peak overnight thermal core energy arbitrage |
| Delivery Temperature | Lukewarm low-flow (35Ā°Cā55Ā°C) | Boiler-matched high-flow (65Ā°Cā80Ā°C) |
| Upfront Grant Eligibility | Ā£7,500 Boiler Upgrade Scheme (BUS) grant | None (does not currently qualify for BUS funding) |
| Radiator Upgrades Needed | Frequently requires larger emitters and wider pipework | None. Drops directly into legacy radiator pipework |
| Acoustic / Space Footprint | External fan unit emits an ongoing hum (~50 dB) | Virtually silent. Completely internal footprint |
| Domestic Hot Water Delivery | Slow, uniform tank reheating loops | Volumetric top-down thermal stratification |
| Annual Service Costs | Annual manufacturer service required for warranty | Almost zero. No compressor loops or fluid packets |
The verdict depends on the property. Where fabric upgrades are realistic, a heat pump offers the lowest lifetime running cost. Where a heritage building, tight budget or disruption limit rules out deep retrofit, the ZEB and Mixergy pairing decarbonises heating without tearing up the building, provided the overnight tariff discipline is in place.