{"id":755999,"date":"2026-08-31T21:52:13","date_gmt":"2026-08-31T21:52:13","guid":{"rendered":"https:\/\/www.newsbeep.com\/uk\/755999\/"},"modified":"2026-08-31T21:52:13","modified_gmt":"2026-08-31T21:52:13","slug":"defeating-bacteria-in-hot-water-systems-with-a-heat-exchanger","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/uk\/755999\/","title":{"rendered":"Defeating Bacteria In Hot Water Systems With A Heat Exchanger"},"content":{"rendered":"

The average hot water is a relatively simple appliance to understand. It uses gas or electricity to dump energy into water in the form of heat, keeping it at a pleasant temperature for uses like bathing and cleaning. Basic mechanisms are in place to ensure the water stays at a relatively constant temperature, neither too hot where it could cause burns, nor too cold such that it wouldn\u2019t be fit for purpose.<\/p>\n

One of the problems, though, is that sometimes storing water at the desired temperature can create the perfect breeding ground for bacteria. However, a neat little trick developed by NIST could solve that problem rather elegantly.<\/a><\/p>\n

You\u2019re Hot And You\u2019re Cold
\n\"\"Legionella pneumophila is a bacteria that loves to grow in warm water. It can enter the body via aerosol and cause of Legionella\u2019s disease. Credit: CDC<\/a>, public domain<\/p>\n

One of the interesting problems of our modern era is that changing our water usage has changed the risk profile for pathogens growing in hot water. NIST has noted for some time that while the pipes in our walls haven\u2019t changed size, things like our shower heads have changed their flow rate to save water. Less flow rate in the same sized pipes means that water stays in the pipes for longer, increasing the time in which harmful pathogens have to grow in that environment.<\/p>\n

Chief amongst these pathogens? The one most commonly feared is legionella pneumophila,\u00a0the bacterium responsible for causing Legionnaires\u2019 disease. The severe form of pneumonia comes with a fatality rate of 10%, and infection typically comes from inhaling aerosolized droplets containing the bacteria.<\/p>\n

Of course, a great way to create aerosolized droplets filled with bacteria is to spray not-quite-hot water through a shower head. This is why hot water systems, particularly in large multi-occupancy buildings, are a risk for such infections. Legionnaires\u2019 disease is rare, but it\u2019s always out there, with 6000 confirmed cases showing up in the US each year. It\u2019s possible that the true number is up to 10 times higher<\/a> because the disease isn\u2019t routinely tested for. The disease\u2019s rarity is in part because engineers and tradespeople put in plenty of work to minimize the ability for the bacterium to breed in hot water systems. As NIST\u2019s work demonstrates, though, there is possibly even more that could be done to tackle this problem.<\/p>\n

Ideally, your hot water pipes in your house would not host\u00a0any nasty bacteria. But often, hot water systems sit around 49 \u00b0C (120 \u00b0F), a temperature that\u2019s hot enough to be useful and pleasant without a major scalding risk. Legionella pneumophila won\u2019t easily grow at that temperature; the bacteria thrives between 20 \u00b0C to 45 \u00b0C (68 \u00b0F \u2013 113 \u00b0F). Unfortunately, though, it\u2019s not hot enough to kill the bacteria completely. Furthermore, water cools as it travels through pipes to an outlet, and thus pipes can be a perfect environment to spur further growth.<\/p>\n

\"\"The solution developed by NIST is simple\u2014jack up the set point of the hot water heater, then fit a heat exchanger on top to cool outgoing hot water with the incoming cold supply. Credit: Brandon Hayes\/NIST\u00a0<\/p>\n

The simple solution would be to simply jack up the hot water system to store water at a much higher temperature, say around 70 \u00b0C (160 \u00b0F).\u00a0 This could be undesirable in many contexts, though, as water that hot can more easily cause burns. It would be ideal to\u00a0store the water at a higher temperature, while making sure it was delivered at a slightly lower temperature so it didn\u2019t hurt anybody when it left the tap or shower head.<\/p>\n

\"\"A prototype unit whipped up by NIST cost only about $100. Credit: NIST<\/p>\n

It turns out that there is a remarkably simple way to achieve this. NIST developed a simple heat exchanger which can be mounted atop any old hot water system. It\u2019s designed such that the hot water leaving the tank passes through a heat exchanger where it\u2019s surrounded by cold water which is running to the water heater\u2019s intake pipe. This has dual benefits. The hot water inside the tank can be stored in the tank at 70 \u00b0C, which kills almost all legionella peumophila almost instantly. That water, though, is then cooled to a slightly safer temperature as it passes through the heat exchanger and out to the tap or shower. The hot water remains at a safe temperature for the user, and contains far less harmful bacteria, and cooling it doesn\u2019t introduce any pathogens from another source. In turn, the cold water coming into the tank is pre-warmed slightly by the hot water, so the energy isn\u2019t simply wasted.<\/p>\n

This trick isn\u2019t just simple, it\u2019s also cheap. NIST engineers were able to fabricate a prototype unit to fit to a residential water heater using just $100 of components. It could be a useful addition for homeowners looking to make their hot water service a little cleaner. However, the real benefits are likely to be for larger operators of multiple-occupancy facilities, like nursing homes and hotels. These facilities often have to take great care to avoid the build up of harmful bacteria in building-wide hot water systems. Having the ability to increase the tank temperature to the point that legionella pneumophila bacteria simply die off would be a huge boon to this effort.<\/p>\n

Sometimes, it\u2019s possible to make great gains with a simple hack. Using the cold water service to cool hotter outgoing water is a smart trick that uses only minimal additional equipment to offer a safer hot water supply. It could yet become a common install for hot water systems in order to fight the good fight against a harmful disease that likes to lurk in our pipes. If you happen to see a heat exchanger atop a hot water heater in future, you can smile that someone has done the work to try and make that hot water supply just a little safer going forward.<\/p>\n","protected":false},"excerpt":{"rendered":"The average hot water is a relatively simple appliance to understand. It uses gas or electricity to dump…\n","protected":false},"author":2,"featured_media":756000,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[59,102,56,54,55],"class_list":["post-755999","post","type-post","status-publish","format-standard","has-post-thumbnail","category-health","tag-gb","tag-health","tag-uk","tag-united-kingdom","tag-unitedkingdom"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/755999","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/comments?post=755999"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/755999\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media\/756000"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media?parent=755999"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/categories?post=755999"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/tags?post=755999"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}