Our methodology

NetZeroNow combines practical guides with lightweight interactive calculators. The tools are designed to help readers compare options quickly, not to replace a professional survey, MCS design, or formal quotation.

Core principles

  • We prefer understandable assumptions over black-box outputs.
  • We surface key defaults on the calculator page wherever possible.
  • We use simple UK-oriented assumptions to produce directional estimates, not guarantees.
  • We revise defaults and page copy when a tool changes materially.

Heat pump estimator

The heat pump calculator works in two modes.

1. Estimated heat demand mode

When a reader does not know their annual fuel use, the tool estimates demand from:

  • property age band
  • property type
  • bedroom count
  • simple insulation and glazing adjustments

The result is an indicative annual heat demand, not a room-by-room heat loss calculation.

2. Manual annual usage mode

If the reader knows annual fuel use, the tool multiplies the entered usage by the selected boiler or system efficiency to estimate useful heat demand.

Output logic

  • Heat pump size is then rounded into broad capacity bands such as 5 kW, 7 kW, 9 kW, 12 kW, or 16 kW.
  • Running-cost comparisons use simplified fuel-price assumptions shown on the page.
  • Heat pump running cost assumes a seasonal coefficient of performance (SCOP) of 3.0.
  • Carbon comparisons use simplified emissions factors to keep the result readable.

Solar potential calculator

The solar calculator estimates annual generation using:

  • number of panels
  • a default panel power of 0.4 kW per panel
  • a base UK yield of 950 kWh per kWp
  • region, orientation, pitch, and shading factors
  • an overall system-efficiency factor of 0.85

Savings are then estimated from:

  • a standard electricity rate of 24.5p per kWh
  • an export rate of 5.0p per kWh
  • self-consumption of 30% without a battery or 70% with a battery

EV charging cost calculator

The EV charging tool estimates annual electricity use as:

annual mileage / miles per kWh

It then compares:

  • charging on a standard tariff
  • charging on a mixed smart tariff based on the user’s off-peak percentage
  • a petrol or diesel comparison vehicle based on pump price and mpg

The petrol comparison converts mpg to litres using the standard 4.54609 litres per imperial gallon. The environmental figure shown on the page is a broad average saving, not a vehicle-specific lifecycle assessment.

U-value calculator

The U-value calculator builds total thermal resistance from:

  • internal surface resistance
  • one or more user-entered material layers
  • external surface resistance

For each layer, resistance is calculated from:

thickness in metres / thermal conductivity

The calculator also includes a simple fixed resistance for an unventilated cavity when that option is selected. The final U-value is:

1 / total resistance

Indicative comparisons on the page use broad UK new-build style targets of:

  • 0.18 W/m2K for walls
  • 0.15 W/m2K for roofs
  • 0.18 W/m2K for floors

Carbon footprint calculator

The carbon footprint calculator focuses on household energy only. It estimates emissions from:

  • heating fuel use
  • grid electricity use
  • on-site generation used to offset household electricity demand

It is intended as a planning tool for retrofit decisions, not as a full lifestyle footprint that includes food, flights, or wider consumption.

What the tools do not do

These tools do not account for every factor that affects final performance, including:

  • unusual occupancy patterns
  • local microclimates
  • detailed emitter sizing
  • installer workmanship and commissioning quality
  • exact tariff terms, standing charges, or regional installer pricing

How we update assumptions

We review assumptions periodically and when a page or tool is updated. Where a calculator uses a fixed default rate or factor, the page should explain that clearly so readers can treat the result as an estimate rather than a promise.

Sources we regularly use

  • GOV.UK for grant and public-service information
  • Ofgem for market and tariff-related context
  • Energy Saving Trust for consumer guidance and benchmark assumptions
  • MCS for installer and technology standards
  • National Grid data for electricity-system and carbon-intensity context
  • Planning Portal for planning-permission guidance in England

Questions or corrections

If you believe a methodology note is unclear or a calculator no longer matches the page description, please contact us or use the feedback page.

Written by NetZeroNow Editorial Team | Last updated on 2026-03-30