Greener Ways to Produce Hot Water Without Gas

Greener Ways to Produce Hot Water Without Gas

Heating water is one of the most expensive things we do with our energy in our properties. Someone told me it takes more energy to heat water than steel.

IT'S TRUE! Water requires 4200 J/kgºC. Steel requires 450 J/kgºC

It is one of the key priorities to decarbonise. At Jigsaw we love the Mixergy cylinders. Reducing the amount of water heated in the first place massively improves a properties levels of energy use and CO2.

One of our contacts, Josiah Lockhart is on his own decarbonisation journey. He has been very busy changing a range of systems and adding others to reduce his energy use in his home. Josiah is keeping a blog on all of the journey he takes. Josiah has recently added a Mixergy to his home. He had a very typical installation of a D rated hot water tank fed by an 8-year-old gas boiler that had around an 80% efficiency rating. He decided to add the new cylinder and Switch from using gas to electric heating of the hot water. Sounds expensive. Not if you do it right and build the system and control it correctly.

Greener Ways to Produce Hot Water Without Gas

Josiah's account of his first few weeks of installation showed a very clear way of saving with some quick changes to his tariff and set up of the cylinder:


"While I only have about 6 weeks data, it is already proving a surprising result. When we compared May and June’s energy consumption (the only pre-micro generation data we will have) I was not expecting the huge change in or usage. At the time we were on the Octopus Go electricity tariff that is .14p per kwh in the daytime and .5p overnight. Both of those are significantly higher than the .3p per kwh we pay for gas. But what emerged once we switched to the Mixergy was that although we increased our electricity usage by around 100 kwh, the more efficient use of the tank reduced our gas consumption by 600 kwh translating to a savings of £64 in June. For the full system including install, we paid £1,531. While that is only one month’s data, even without our switch to solar, early indications are that the Mixergy would pay for itself in roughly 20 months."


Josiah has stated to me that these are only initial readings and that he will monitor it further. What I have found from my own Mixergy cylinder is that you actually find ways to reduce the running cost of the system further.

Greener Ways to Produce Hot Water Without Gas

Here's my top tips:

1, Reduce your minimum levels of water in the cylinder - What do you actually use, do you ever run out? Easily a 10-20% saving. I only store 20% max during the day of my 180l tank. By the way a 180l tank for a family of four is way too big. The 150l would have been fine.


2, Set your holiday mode - If you're away set your dates. Don't waste energy!!!! Easy 2-3 weeks of energy there. My previous system was so difficult I didn't bother. With the Mixergy app I press the button and set the dates.


3, Check your schedule - Heat the water just before you need it. People are creatures of habit. We get up and go to bed at roughly the same times everyday. My cylinder is set for a charge just before I get up and the kids baths just before they have them. No wastage there.


4, Don't heat if you don't need it - I have a schedule set every morning and evening to boost before showers and evening meal/kids bath. The kids don’t always have an evening bath. Stop the boost. Mixergy - please add a quick "cancel next heat time" button somewhere. I calculated it costs me over £60 per year just for the kids baths. Let's save some energy there.


5, Heat the water when it's the cheapest - Some tariffs are cheaper overnight. It sometimes works out more cost effective to overheat the cylinder at this point. You overheat it because there will be some energy lost from the cylinder over a period of time. Some smart tariff are free or pay you when there is a surplus. Octopus paid me to charge my cylinder on a trial of the renewable grid. Thanks!

As with all things, the proof is in the pudding. I use it, so do others at Jigsaw. The simplicity of it makes it a pleasure to use. Josiah's blog is a great way to show the early evidence of this. You can see more from Josiah and his journey in to decarbonisation here (

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