I have been monitoring my new Combisave device over the past month and have now enough data to calculate some initial findings in terms of water, gas and time savings.
Serendipitously, June is a perfect month to monitor gas use for hot water heating, as even with the non-summer we have been having lately, we have not put the heating on at all through the past month, and as I do not cook with gas, the only gas use through the summer months is for hot water use. Also, luckily, I have monthly readings of summer month gas usage for the last two years (yes, I know, I'm a bit geeky) and so have a high level of certainty about my household's daily summer gas usage – typically averaging 5.18 kWh per day (as measured over June-Sept 2011).
Also, usefully, I have been on a water meter for years, so can also easily calculate a daily summertime water usage volume from my previous bills. Typically, for our two person household it has been around 200 litres a day.
So, how has the Combisave device performed in this past month. Roll of the drums please…
In the month of June we used a total of 5470 litres of water (this includes 2 short hose pipe uses, after the hose pipe ban was lifted I hasten to add), that works out at around 90 litres per person per day. Typically, in years past, we have used an average of 100 litres per person per day in the summer months. So that is a 10% potential saving. The only other variable in this is the fact that, in years gone past, we might have used the hose pipe more for watering the garden, as the summers have been a little better and drier in recent years! So it is not totally conclusive.
Turning to the gas saving, which can be more conclusive, I have seen an average daily usage of gas of 4.77 kWh per day in June. So, we can say that there is probably a small gas saving through the use of the Combisave device of 0.41 kWh per day.
In terms of a time saving, well, it hasn't saved me any time at all in the mornings whilst waiting for the shower to warm up (if I'm first in), it's still just over a minute's wait unfortunately.
To put some monetary savings to these figures:
Water: If we are, on average, saving 20 litres of water per day, then total yearly savings could be around 7300 litres. Now, the average metered price for water in the UK is about 0.25 pence per litre. So we can calculate that my yearly savings on my water bill could be around the £18 mark.
Gas: If I am saving 0.41 kWh per day on my gas usage for water heating, that will amount to about 150 kWh of gas saved per year. Using an average gas price of 4.5 pence per kWh unit, my yearly saving on my gas bill could be around £6 – 7
That gives me a total combined water and gas saving of approximately £25 per year
So, given a total installed price for the Combisave of approx: £130 (made up of the price of the unit plus the plumber's installation charge – but this will vary), we are looking at an approximate 5 year payback. Which is reasonable, as the lifetime on the device is said to be 20 years or more.
I'm happy with this, and am glad I invested in the device. However, what I am not so comfortable with is the extraordinary claims that Combisave have on their website regarding the potential savings that people can make with their gadget. I feel people would be quite happy with a 5 year payback (or more than likelyless for a bigger household) and then ongoing, year on year, savings on their gas and water usage (if on a meter), there is really no need to 'over promise' to such a significant degree, only to really cheese people off when they do not achieve those savings after installation. That isn't the way to get 'word of mouth' recommendations for your product.
So come on Combisave, your product has merit, please don't spoil it by extraordinary, and, in my opinion and personal experience, overblown claims of monetary savings that it will simply not deliver.
Related blog post on the subject: http://paulaowenconsulting.co.uk/2012/05/31/the-trouble-with-combination-boilers-a-new-gadget-to-potentially-save-water-and-energy/