HEAT PUMPS


replacements for gas boilers. Obviously, we need to heat our homes in winter at least for comfort and in the case of the vulnerable, to protect against hypothermia. Although in the past we Brits have not viewed our summer weather as a threat to health, this is changing, evidenced by four heat waves in 2025 and the record UK temperature of 40.3 °C in 2022, substantially exceeding the previous 2019 record of 38.7 °C. Britain has a problem whether these high temperatures were caused by anthropogenic greenhouse gas emissions, or result naturally from increasing energy from the Sun, a view espoused by Reform UK. Heat stress from heat waves is recognised as a major contributor to weather-related deaths, aggravating systemic illnesses such as diabetes and asthma. A hot spell is classed as a heat wave if it lasts for a minimum


of three consecutive days when the maximum temperature equals or exceeds the regional threshold. The central and southern England threshold is 26-28 °C, but 25 °C in the rest of the UK. We no longer fi nd these temperatures unusual. High


night-time temperatures in particular seem to cause excess mortality. France has experienced signifi cant extra deaths due to heat, with an estimated 37,825 estimated between 2014 and 2023. In the summer of 2023 alone, 5,167 deaths were linked to heat, with the most vulnerable being the elderly, infants, and children. Studies show that the risk is particularly high in cities like Paris, which is only 200 miles from London. UK Government policy to achieve net-zero greenhouse gas emissions by 2050 will not prevent increasing excess mortality since the heat wave frequency will continue to grow. Installing monobloc heat pumps, which can only provide heating, seems therefore somewhat perverse. If they were reversible systems, available to provide summer cooling as well as winter heating, they could help alleviate heat wave excess mortality. Some might argue that even with global warming, the UK summers will still be bearable for most people most of the time, but this would assign individuals susceptible to the excessive heat to early deaths. Furthermore, air-to-air systems are more energy effi cient than air-to-water because they operate with lower condensing temperatures. Despite helping to reduce CO2


emissions, heat


pumps are still net contributors, while our electricity is at least partly dependent on fossil fuel generation. Environmentally, it makes good sense to maximise their effi ciency. For new-builds this could mean adopting reversible unit systems common in North America, that use air ducts to distribute heat and coolth. For existing US homes lacking ducting, reversible ‘mini-splits’ are seen as an effi cient, viable alternative, although this would require stripping out all existing hot water central heating pipes and installing refrigerant lines.


But for better or worse, the UK is going down the air-to- water monobloc path. Having splurged out £10K in 2025 for an air-to-water heat pump, a householder may resent fi nding a further £2k for a split a/c unit for the bedroom to get a good night’s sleep and a further £2k to cool the lounge. Probably acceptable if you have the cash, but rather less attractive if you are still paying off a loan for the heat pump. Maybe a monobloc heat pump could be adapted to


provide cooling, or am I indulging in a Red Queen fantasy of believing an impossibility before breakfast? Suppose a 4-way reversing valve was incorporated into the unit, and one or more ‘radiators’ were replaced by fan-forced convection heat exchangers in key rooms. During a heat wave, the heat pump would function as an air conditioning unit cooling a portion of a dwelling. So how could this confi guration infl uence the selection


of refrigerant, at least in heat pump mode? A wide glide refrigerant such as R470A that condenses over a range might be suited to providing higher temperature water suitable for the natural convection radiators. Subsequently, it could fl ow at a lower temperature through the forced convection radiators, where the air fl ow enhances heat exchange. The overall eff ect might be an improvement in energy effi ciency. But maybe like the Red Queen, I am believing in an impossibility before breakfast.


'Driven by government policies and supported by grants, ‘monobloc’ air-to-water heat pumps are the major de facto


replacements for fossil-


fueled boilers in existing homes. New- builds must have low-


carbon heating systems from this year (2025).'


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