Why a plain-English explainer
Most writing about heat pumps is selling something: a product, an installation or a grant application. That makes it hard to find a straight explanation of how the machine works, what its efficiency figures mean and how to compare its running cost fairly. This site tries to do only that, and to show where every number comes from.
What it covers and what it leaves out
It covers the refrigerant cycle, the types of heat pump, efficiency (COP, SCOP and SPF), flow temperature, hot water, cold weather, controls, noise, tariffs and the price of a unit of heat. It leaves out installation steps, installer checks, detailed grant eligibility and local information, which other sources cover.
Who publishes it
Published by SEO-DONS LTD (company no. 16766013), 71-75 Shelton Street, Covent Garden, London WC2H 9JQ. The company's record is on Companies House. There are no named authors; pages are written and checked by the publisher.
What it is not
It is not an installer, manufacturer, retailer or adviser, and it is not part of any government department or grant scheme. It does not list, rate or recommend firms. For certified installers, MCS keeps the official register; RECC and HIES are the consumer codes most heat pump installers belong to, and TrustMark runs its own quality scheme. Any warranty on a system is between you and the firm that fits it.
How it is kept accurate
Every figure comes from a named source, listed on each page and on the sources page. Calculations are shown, assumptions are labelled, and we review each page when one of its sources changes.
Questions and corrections
The form below reaches the publisher, who replies by email. Your details are not passed to any installer.
Why prices per unit of heat, not savings
Many calculators online promise a yearly saving. We chose not to build one, because a yearly figure needs facts a web form cannot know: how much heat the home loses, how the system will be designed and controlled, and how the household lives. What can be worked out honestly is the price of one kilowatt-hour of heat from each system on a given tariff, and that is what our calculator shows.
How we treat efficiency claims
Efficiency is the number everything else depends on, and it is quoted in three different ways. Wherever this site gives a figure, it says which kind it is and where it came from, and the default used in calculations is a measured field median rather than a laboratory best case.