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# John Cantor Heat Pumps

Heat pump information without the hype...

## Sitemaps

- [XML Sitemap](https://johncantor.uk/sitemap.xml): Contains all public & indexable URLs for this website.

## Posts

- [Blog](https://johncantor.uk/blog/)
- [My Website has moved to here!](https://johncantor.uk/2026/02/16/my-website-has-moved/) - (Blog index) I have had a heat pumps website for 30 years. It has always been an unbiased (I hope!) source of information, and now its content has moved to here. — I’m still here! I have now officially retired , but the website content will live on much as it always has. It still includes,
- [Badly performing heat pumps??](https://johncantor.uk/2021/10/28/badly-performing-heat-pumps/) - Index of my blogs Are some heat pumps performing as badly as various recent stories have been reporting? Let’s imagine if we procured cars in the same way that some people install heating. We could start with a body shell, then get someone to fit wheels to it, hopefully placed in the best position and
- [Study on an air-to-air heat pump](https://johncantor.uk/2025/06/16/air-air-v-air-water/) - (Blog index) The most common and popular Air Source Heat Pump (ASHP) is the monoblock type that produces water, piped into the house for use in conventional radiators or underfloor heating. In the UK, blown-air heating is uncommon. However, an alternative type of heat pump (air-to-air) does exactly that – it heats the air directly.
- [Repairing a heat pump -   How well is it carried out?](https://johncantor.uk/2012/05/02/repairing-a-heat-pump-how-well-is-it-carried-out/) - This post is a little specific, and discusses the need for care and consideration when carying out any 'major surgury' on a heat pump. A little extra time setting the system up right will save considerable energy (and money) over its life. A domestic fridge will generally complete its useful life without encountering any problems
- [Heat Pump Performance Monitoring Examples](https://johncantor.uk/2015/09/09/heat-pump-performance-monitoring-examples/) - This is an old blog but may be of interest to a few OpenEnergyMonitor are going strong. See 2020 update here Summary of a brief presentation at the Ground Source Heat Pump Expo at the Ricoh Arena on the topic ‘Energy or Performance Monitoring’, so its timely to do a little blog here to elaborate
- [Temperature sensing with OpenEnergyMonitor](https://johncantor.uk/2015/06/08/temperature-sensing-with-openenergymonitor/) - Temperature sensors for monitoring heat pumps (Written 2015) I have been using OpenEnergyMonitor.org energy monitors with heat pumps for a few years now and thought I should briefly share my experience. This covers the practical side of temperature sensors, and is based on my experience. (If you just want advice about fitting temperatures sensors onto
- [Radiant temperature.  Elephant in the room?](https://johncantor.uk/2021/03/09/radiant-temperature-elephant-in-the-room/) - In a cold un-heated exhibition room at the Centre for Alternative Technology many years ago, there was one of those good-for-your-posture kneeling chairs. Surrounding this chair was a curved hardboard sheet covered with Aluminium foil. You were invited to sit, surrounded by a shiny foil surface. The effect was quite dramatic, you could instantly feel
- [Potential perils of plastic pipe](https://johncantor.uk/2014/02/20/potential-perils-of-plastic-pipe/) - (Note, if you are reading this you might also be interested in my flow/pressure simulator) A college tutor recently suggested to me that the current environment in the heating industry does not encourage analytical thinking. Maybe I should therefore be less amazed when I come across plumbers who think copper and plastic pipe are
- [Distributing hot water to tap outlets](https://johncantor.uk/2017/04/16/distributing-hot-water-tap-outlets/) - To my mind, the whole point of having a heat pump is to save energy, so it somewhat jars with me when I see one aspect of a system that is not in-line with that aim. A heat pump always stores Domestic Hot Water (DHW) in a cylinder. The Cylinder is, we hope, sized and
- [Heating Simulator](https://johncantor.uk/2021/03/11/heating-simulator/) - This is fantastic! I have wanted to do this sort of thing for ages, and now thanks to my niece Ellie who constructed it, it's working! Click here for a full screen version of the Simulator below What is the purpose of this simulator? What happens when we slow-down the flow rate? What would happen
- [Getting the best from underfloor heating](https://johncantor.uk/2014/03/06/getting-the-best-from-underfloor-heating/) - [Note, this blog was published 2014.. the underfloor heating industry has developed a lot in the last 5 years] Many years ago, when heat pumps were not so common, I found it a real struggle to get any of the main underfloor heating suppliers to embrace the need for low water temperatures for use with
- [Is a reversible air-air heat pump a proper heating system?](https://johncantor.uk/2021/07/21/is-a-reversible-air-air-heat-pump-a-proper-heating-system/) - Index of my blogs I have pondered this many times, and indeed, a district council once asked me this very question. They ended up getting me along to analyse why some of their tenants, who had this type of split reversible air-conditioning, had warm houses, low bills and loved them, whist others hated them, complained
- [Heat Pumps and domestic hot water](https://johncantor.uk/2021/08/07/heat-pumps-and-domestic-hot-water/) - (Index of other blogs) Before I start, I hope nobody takes from this that we shouldn’t do domestic hot water (DHW) with HPs. And as things evolve, I’m sure that we will do more of it, and do it better. However, I was pondering the issue of mass adoption of HPs for smaller houses and
- [Heating old buildings with heat pumps](https://johncantor.uk/2020/11/03/heating-old-buildings-with-heat-pumps/) - Also see YouTube here (index of other blogs) It’s great to see how heat pumps are becoming mainstream, and increasingly the norm for newbuild. However, I have noticed ongoing confusion relating to the use of heat pumps in
- [Pressure drops, flow-rates and LENGTH](https://johncantor.uk/2017/03/29/pressure-drops-flow-rates-length/) - (Note- if you are reading this.. you might also be interested in my new flow and pressure simulator) “What is the point of having a large diameter pipe run when the fittings on the heat pump are small?” I have heard that statement enough times to make me want to write a blog about it.
- [Heat pump controls, we need better](https://johncantor.uk/2021/02/16/1698/) - These blogs are usually triggered when I come across issues (several times) that bother me… here goes. Theory and practice show that the best performance for any (1) heat pump is achieved if the average water temperature that the heat pump ‘sees’ (the water temperature passing through it) is kept low (2), whilst still achieving
- [Underfloor heating in bathrooms (from 2012)](https://johncantor.uk/2012/08/02/underfloor-heating-in-bathrooms/) - A bathroom has a higher room temperature requirement, so heat requirements are generally higher, but the floor area available for underfloor heating is reduced due to the area taken up by the bath. I have recently come across a few instances of inadequate heating issues in bathrooms – not surprising. The point of this blog
- [Kilowatts per hour! A guide for the perplexed.](https://johncantor.uk/2018/02/19/kilowatts-per-hour-guide-perplexed/) - There is a little detail that annoys many people. It’s the confusion that seems to arise over the commonly used units of energy and power I came across this the other day and pondered why it's a common error. When we drill into the details, we can see why confusion could arise. We are all
- [Legionella protection and energy](https://johncantor.uk/2012/12/08/68/) - Legionella protection and energy demand It is poignant that I write this whilst a hot debate continues in Doha, Qatar over the issue of climate change, which is more evident in some poorer parts of the world, and the proposal that the energy-guzzling West should compensate in some way. This seems to put my blog
- [Selecting the right Heat Meter.](https://johncantor.uk/2016/06/08/selecting-the-right-heat-meter/) - This topic is VERY IMPORTANT I am aware that the pressure requirements of heat meters is often overlooked - this can be detrimental to a heat pump system. A heat pump will normally be connected to a radiator or underfloor heat-emitter circuit. A circulation pump (circulator) is required to ‘force’ the water around this
- [Stand-by power and air-source heat pumps](https://johncantor.uk/2013/08/13/stand-by-power-and-air-source-heat-pumps/) - I have been aware for some time that my 5kW air-source heat pump (ASHP) has been using about 3/4 of a kWh/day whilst doing 'nothing' over the summer (no circulation pumps running), but recently I have put energy monitors on other ASHPs and was shocked see that these known-brand units are using 2kWh/day when doing

## Pages

- [Heat Pump Information](https://johncantor.uk/) - Explore 45 years of expert insights on heat pumps, designed for beginners, students and experienced alike, including educational simulators and calculators
- [Keeping cool in a heatwave](https://johncantor.uk/keeping-cool-in-a-heatwave/) - Keeping buildings cool in a heatwave Heat waves are generally short-lived in the UK so it is not surprising that we are not very good at dealing with them. Here is the main problem. ... Sun shines in through windows and heats any surface it falls on, and this heats the room. In hot countries,
- [Calculators & Simulator](https://johncantor.uk/calculators/) - On this page below you can find some useful tools for back-of-envelope estimates of ...... 1) Water volume, Cylinders & Buffers, 2) Flow-rates, 3,4,5) Radiator temperature, heat output and Area. 6)
- [Heating Simulator](https://johncantor.uk/calculators/heating-simulator-for-radiators/) - click here for full screen or YouTube explanation or 'type-in-the-numbers' version (1/2 way down page) What is the purpose of this simulator? What happens when we slow-down the water flow rate? What would happen if we double the radiator size? What happens to the water temperatures if we change various things? This very useful 'simulator'
- [Blog Index](https://johncantor.uk/blog/blog-index/) - Index of Blogs by John Cantor Please note, some of the blogs at the bottom are quite old now . Bear that in mind when reading them. ( see my YouTube videos too ) My website has moved to ... here!. Feb 2026 Testing an air-to-air heat pump in real life 04/Jan./2025
- [About us](https://johncantor.uk/about-us/) - The company was established in 1980 and in the early days had close links with The Centre for Alternative Technology in Wales. During the 80's I designed, manufactured and installed (in small numbers) a wide variety of water-to-water heat pumps with power-output capabilities from 1Kwatt to 70Kwatts. Some of our earliest installations were still in
- [Types of heat pump](https://johncantor.uk/types-of-heat-pump/) - Heat pumps come in many forms. The most common types are summarised as follows Reversible air-conditioners / heat pumps - air-to-air These are very widespread, especially in warmer climates. They can provide heating, but may not be considered be the best appliance for ‘proper’ house heating. (But read my blog!
- [What is the COP?](https://johncantor.uk/heat-pump-information-without-the-hype/what-is-the-cop/) - The energy-efficiency of a boiler is usually quoted in percentage terms. e.g. If a boiler is said to be 90% efficient, then 90% of the gas energy ends up as useful heat to water, and 10% is lost as heat out of the flue. Heat pumps require electricity to function. They transfer heat from outside,
- [How does a heat pump work?](https://johncantor.uk/heat-pump-information-without-the-hype/heat-pump-work/) - This apparently 'magical' device is far from new. At first it seems counter-intuitive, but how a heat pump works actually makes sense given a little thought See my Youtube video HOW CAN HEAT BE EXTRACTED FROM COLD WATER? Our natural sense of heat is based more on instinct than on science. Humans are warm-blooded and
- [What is a heat pump?](https://johncantor.uk/heat-pump-information-without-the-hype/what-is-a-heat-pump/) - The term ‘heat pump’ is very descriptive. It's a device that ‘transfers’ or ‘pumps’ heat from one place to another. You probably own a heat pump without realising it – a refrigerator is actually a heat pump, and it transfers heat in the opposite direction to its natural flow. It extracts heat from the icebox
- [Energy Saving Tips](https://johncantor.uk/heat-pump-resources/energy-saving-tips/) - This page gives some very general energy-saving discussion. (Click to Jump to heat pumps below) 1. Consider some SERIOUS insulation. Consider what savings would be made over the lifetime of the building. Wall insulation is important. Internal insulation can be done room by room by various methods. External wall insulation may be an expensive option,
- [Radiators](https://johncantor.uk/types-of-heat-pump/delivering-the-heat/radiators/) - NEW.. Try this simulator click here Commonly called a radiator, this simple steel 'envelope' of hot water will actually convect more heat than it radiates. Most heat comes from the warm air rising from it. Radiators are often the only option simply due to the lower installation cost and minimal upheaval. In the old days
- [Underfloor heating](https://johncantor.uk/types-of-heat-pump/delivering-the-heat/underfloor-heating/) - Underfloor heating can be an ideal choice for a house with a heat pump. However, it is not always viable or practical to install. The area of the floor is very large so the temperature of the floor, and water pipes below it, may barely feel lukewarm. This is ideal for a heat pump.
- [Air Source Heat Pumps (ASHP)](https://johncantor.uk/types-of-heat-pump/air-source-heat-pumps/) - Reversible air-conditioning / heat pump Many of the wall-mounted air-conditioners that you see outside offices and shops are reversible. These can operate in heating-mode as well as cooling. They are often optimised for cooling mode, so their energy efficiency in heating-mode can be inferior. Systems specifically designed for heating have been with us for some
- [Archive](https://johncantor.uk/archive/) - Click on the links below The tale of Lazonby, Greystoke and Askham swimming pools from 1982 Photographs from 1982 Graphs and charts of the pool heat pumps Some old archive photographs
- [COP comparator](https://johncantor.uk/calculators/cop-estimator/) - COP (Coefficient of performance) ... the energy-efficiency) This is a simple calculator using the Carnot efficiency equation. It uses the refrigerant temperatures to estimate the approximate COP. The actual real-life COP is usually about 50% of the theoretical Carnot COP. (see further info at the bottom). Note - This is only an estimate for one
- [Viability and economics](https://johncantor.uk/viability-and-economics/) - Heat pumps are one option for reducing the carbon footprint of a building. They have been around for many years, and were well established 30 years ago in Sweden, Germany and North America, so the technology is very well-developed. Running cost can often be lower than traditional heating systems, but this is not always the
- [Domestic Hot Water (DHW)](https://johncantor.uk/types-of-heat-pump/domestic-hot-water-dhw/) - In the past, hot water was only a small percentage of a building's total energy demand (e.g. 20%). However, as the insulation levels of buildings increase, and the space-heating demand drops, the proportion of heat directed to DHW increases. Furthermore, our hot water use for washing and showering has if anything increased - we are
- [Distributing the heat](https://johncantor.uk/types-of-heat-pump/delivering-the-heat/) - How is the heat distributed around the building? Heat pumps have become more and more viable over the last 10 years. This is in part because they have evolved and are also more energy-efficient, but mostly because the mains electricity that enables them to work has become 'greener'. This increase in viability has meant that
- [Water source heat pumps](https://johncantor.uk/types-of-heat-pump/water-source-heat-pumps/) - Surface water, rivers, lakes and spring water source heat pumps Rules and regulations and the lack of available manufactured equipment have made this type of system less attractive. That said, there may be a increased interest in this method since it can have advantages over other systems if the situation is right. Springs Deep ground
- [Ground Source Heat Pumps  (GSHP)](https://johncantor.uk/types-of-heat-pump/ground-source-heat-pumps/) - Ground Source heat pumps (GSHPs) extract heat stored in the ground, and promise to deliver good year-round energy-efficiency, and can offer considerable long-term environmental advantages. 'Ground source' was occasionally referred to as ‘geothermal’. However, the heat is mostly from the surface (solar gain), and very little is from the earth’s core. (‘Proper’ geothermal is found
- [Heat Recovery Ventilation](https://johncantor.uk/technical/mechanical-heat-recovery-ventilation/) - Mechanical Heat Recovery Ventilation (MVHR)
- [Book, Heat Pumps for the Home](https://johncantor.uk/book-heat-pumps-home/) - Heat Pumps for the Home Author John Cantor Illustrator Gavin Harper Crowood Press ISBN 9781785007798 158 pages, 155 colour photographs and diagrams Second edition release date - November 2020 Heat pumps are surprising devices that can extract heat energy from something that appears to be cold - from the air or the ground for
- [Glossary of heat pump terms](https://johncantor.uk/heat-pump-resources/glossary-of-heat-pump-terms/) - Active cooling Normal heat pump cooling, as opposed to ‘passive’ or ‘free’ cooling Air conditioning Originates from the system that both cools and controls the humidity of air in a building. It is now loosely used to describe any room cooling application. Air - Air Heat Pump A heat pump which uses air as the
- [Energy Monitoring](https://johncantor.uk/technical/energy-monitoring/) - Now we have the internet everywhere, it is relatively easy to collect temperature and power readings from any equipment, and to send it to [amps] website for viewing anywhere. Many manufacturers have developed such systems to monitor their equipment. Not only does it help the owner to understand how the system is working, but it
- [Technical](https://johncantor.uk/technical/) - Soory, not much here at present Energy Monitoring Fixing old Honeywell Mixing Valves These valves often stick after many years use. They are a good design, and made so the cartridge can be replaced. These valves are built to last!
- [Honeywell VC series diverter valve. Stiebel Eltron Nibe and others](https://johncantor.uk/technical/stiebel-honeywell-vc-series-diverter-valve/) - This VC series diverter valve was fitted to most Stiebel Eltron Ground Source units, and many others. It diverts the flow to either heating or hot water (DHW) modes. (it's either/or and does not blend). It is not uncommon for them to stick either half-way, or stick in DHW mode. It's incredibly easy to remove
- [Environmental](https://johncantor.uk/environmental/) - Climate Change Effects Large amounts of energy are used for heating our houses, and our initial focus should be to minimise the heat requirements by normal conservation measures like insulation. This is certainly the best and simplest first-step. Sadly, we cannot all live in super-insulated eco-houses, so significant amounts of heat energy are still required
- [Lazonby swimming pool river-source heat pump data](https://johncantor.uk/archive/tale-3-swimming-pools/lazonby-swimming-pool-river-source-heat-pump-data/) - Note, The original boiler was 65% efficient. In 1982, a new boiler could have been 88% efficient (in theory). Pool open May to early September. Heat Pump COP of 4.25 estimated. Swimming pool heat pump pollution figures for various fuel types. 1 Pollution figures for oil 0.27 kg CO2/ Kwhr Boiler efficiency 65 % Net
- [Old swimming pool photo gallery](https://johncantor.uk/archive/tale-3-swimming-pools/old-swimming-pool-photo-gallery/) - Heat Pump installations at 3 Community swimming pools close to Penrith Cumbria Photographs taken during 1982 & 1983 Lazonby swimming pool on a nice warm summers day. JCB about to cross the river Eden Slowly does it. Making the hole for the ring where the water pump will go. Positioning concrete ring Digging trench up
- [Archive photographs](https://johncantor.uk/archive/archive-photographs/) - A few Archive pictures When it all began. 1979 Comtec festival Milton Keynes. A cycle-powered demo of the heat pump principal. An old paint can of water is heated to 'quite hot' by extracting heat from the air. So, here is a challenge 44 years on... Replicate this model for the CAT 50th birthday on
- [Photographs of heat pumps](https://johncantor.uk/archive/photographs-heat-pumps/) - Here are a few interesting pictures An Ecoforest ground source heat pump installation. This unit has an inverter drive that varies the heat output from about 4kW to 12kW. The Kamstrup heat meter is showing us that the energy-efficiency is very high. No buffer tank is usually needed. Below; Good old Swedish IVT
- [Useful Links](https://johncantor.uk/heat-pump-resources/useful-links-2/) - Grants and funding for heat pumps. Renewable Heat Incentive (RHI) ended earlier in 2022 in the UK. The Clean Heat Grant, also known as the Boiler Upgrade Scheme , is a government scheme launched in spring 2022. This is a £7,500 payment administrated via an MCS accredited heat pump installer. It is likely to run
- [Frequently asked questions](https://johncantor.uk/heat-pump-resources/frequently-asked-questions-heat-pumps/) - I’m told that I need to run my radiators at a lower temperature if I have a heat pump fitted, but how will I still be warm? This could seem a confusing topic. Let’s think firstly of how radiators are normally controlled. A boiler system is traditionally designed so that radiators turn themselves on or
- [Glossary](https://johncantor.uk/heat-pump-resources/glossary/) - Active cooling Normal heat pump cooling, as opposed to ‘passive’ or ‘free’ cooling Air conditioning Originates from the system that both cools and controls the humidity of air in a building. It is now loosely used to describe any room cooling application. Air - Air Heat Pump A heat pump which uses air as the
- [Numbers and calculations](https://johncantor.uk/calculators/numbers-and-calculations/) - It is always important to do simple calculations. This is FAR FAR better than going by gut feeling and guesswork. That said, don't blindly trust calculations. e.g. do some simple calcs.. make other comparisons to verify your assumptions are correct. (also see Calculators) Some useful figures and conversions 1 kW (kilowatt) is a unit of
- [COP comparator (Fahrenheit)](https://johncantor.uk/calculators/cop-estimator/cop-estimator-comparator-fahrenheit/) - This is a simple calculator using the Carnot efficiency equation. It uses the refrigerant temperatures to estimate the approximate COP. The actual real-life COP is usually around 50% of the theoretical Carnot COP. (see further info at the bottom). Note - This is only an estimate for one point in time. Various things affect the
- [Pressure drops and flow rates](https://johncantor.uk/calculators/flow-rate-and-pressure-drop-simulator/pressure-drops-flow-rates/) - LENGTH is just as important as pipe diameter Try this flow-rate and pressure-drop simulator [ Note- a simpler blog on this topic is here ] It is very important to choose the correct diameter pipe for any pipe run. Unfortunately, pipe sized are sometimes guessed. If the pipe is the wrong diameter, then problems may
- [Flow-rate and pressure-drop Simulator](https://johncantor.uk/calculators/flow-rate-and-pressure-drop-simulator/) - Click here for full page version and here for a YouTube explanation  All ‘wet’ heating systems involve 'pushing' heated water through pipework circuits. A circulation pump is used to create the ‘push’, and the bore and length of all the sections of pipe and fittings is what it’s working against. For pipes and components
- [Book Index 2nd edition](https://johncantor.uk/book-heat-pumps-home/book-index-2nd-edition/) - Heat Pumps for the Home 2nd edition Due to Covid, the index was not updated on some copies of the book. You can print this and pop it in the back INDEX absolute zero 10, 16 absorption cycle 24 air conditioning 27, 68, 84 air heating 68 air source 27-9, 46, 93, 97, 108, 127-130
- [A tale of 3 swimming pools](https://johncantor.uk/archive/tale-3-swimming-pools/) - Swimming pool heat pump systems installed by John Cantor in the spring of 1982. Lazonby river sourced system (River Eden) Greystoke air-sourced system. Askham air source system (installed 1983). Old swimming pool photo gallery I had escaped busy London back in 1979 and had moved to a small village called Renwick near Penrith. I was
- [Refrigerants](https://johncantor.uk/environmental/global-warming-potential-of-refrigerants/) - REFRIGERANTS (the working fluid inside the heat pump) ( See my 12 minute YouTube video on refrigerants ) Every normal heat pump and fridge uses a fluid to enable the heat transfer. This pressurised fluid evaporates and condenses in different heat-exchangers in the unit, and there are a limited number of suitable fluids that will
- [Financial incentives for heat pumps](https://johncantor.uk/viability-and-economics/rhi-financial-incentives-for-heat-pumps/) - The now-ended Renewable Heat Incentive (RHI) was an incentive scheme that paid you a tariff depending on how much heat is used. It finish early in 2022. The RHI was substituted by the Boiler Replacement Scheme in Spring 2022. The Scheme is grant of £5,000 for Air source (ASHPs) or £6,000 for Ground source (GSHPs),
- [Heat Pump resources](https://johncantor.uk/heat-pump-resources/) - Glossary of terms Frequently asked questions Useful links

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