This is the nearest cheap solution I've seen: https://www.linkedin.com/pulse/greatest-innovation-heat-pumps-2021-how-cut-your-pump-graham-hendra/, although it uses the immersion heater to do the boost heat to 60deg.

Just means the normal tank stat can be set to (say) 50deg and then the timer is set to turn the immersion on after a normal HW heating cycle to do the final boost heat once a week.

Hi @cycleneil

As with many other situations in life, there are often different ways to achieve the same objective. When it comes to providing hot water, this can be achieved in the most cost effective manner, the most energy efficient manner, or hopefully a combination of the two. Much depends upon your present system, how you wish to operate this system, and if you are willing to improve your present system.

With just your present ASHP, the most energy efficient and probably most cost effective manner to provide hot water, would be to heat it using solely the heat pump. Whether you do this during the cooler nighttime, during the warmer part of the day, or a combination of the two, would depend on your daily usage and preferences. I will go through the various options.

If you are on a lower cost overnight electricity tariff, then it should be much more cost effective to produce your hot water using your ASHP during this period, but since your heat pump will not be operating as efficiently, it will use more energy. Once per week, or as recommended by the heat pump manufacturer, it would also be possible to perform the disinfectant heating cycle, using solely your heat pump if it is capable, or a combination of heat pump and immersion heater.

If you are not on a lower cost overnight electricity tariff, then producing hot water during the warmer part of the day should be more efficient and less expensive. Heat pumps operate more efficient when the outdoor air temperature is warmer.

The above two methods should apply equally to both Winter and Summer.

If you are fortunate enough to have a suitably sized solar PV system, or contemplate installing one, then from Spring through to Autumn it should be possible to supply a large proportion of your hot water needs, at very little cost and energy consumption. Such a system should also be possible to perform the disinfection cycle in most cases. A suitable electricity diverter unit would also be required along with the solar PV system.

An alternative method to provide hot water would be using a solar thermal system, which whilst not as versatile as solar PV, is in fact much more efficient. Such a system would probably require a hot water cylinder with dual heating coils. I do believe that solar thermal is cheaper to install than solar PV.

The above two methods obviously will not be able to supply all your hot water demand during the Winter months, when an alternative source will be required.

Hi @derek-m 

I wasn’t necessarily thinking about an ASHP system, or a situation with PV, just how a boiler-based heating system could be made more efficient given that most are pretty dumb!

Posted by: @cycleneil

Hi @derek-m 

I wasn’t necessarily thinking about an ASHP system, or a situation with PV, just how a boiler-based heating system could be made more efficient given that most are pretty dumb!

Hi Neil,

What is your boiler based system, and what exactly are you trying to achieve? From my understanding, running a gas or oil boiler at higher temperatures does not affect its overall efficiency to the same degree as with an ASHP.

@derek-m Just to save the energy needed to raise the HW temp to 60deg when 50deg is sufficient normally.

Posted by: @cycleneil

@derek-m Just to save the energy needed to raise the HW temp to 60deg when 50deg is sufficient normally.

Hi Neil,

I appreciate that, but without knowing what system you have at the moment and how you are operating it, I can hardly give any advice on how it may be improved.

@derek-m The house I am buying has oil heating with a 20 year old non-condensing boiler, but I plan to do nothing to the system for 1 winter while I see what the fabric is like after I have replaced the windows and doors and improved the loft insulation.

From my quick inspection while deciding to purchase, it has a simple on/off timed program control system for heating and h/w with a simple bimetallic tank stat which I expect is set at 60deg. It looks to have a fairly new unvented h/w tank, so I’d expect that to be decently insulated.

I was just looking for some simple/cheap energy saving wins that will work with a dumb system before I make some proper decisions in 2023.

Hi @cycleneil

I have had a quick look on the internet for a suitable device to replace your present thermostat, but I cannot find a simple solution.

The only thing that I can suggest at the moment is to set your present thermostat at 50C, or whatever setting that you desire, and then once each week or so turn it up to 60C for a period of time. Since you have a non-condensing boiler, I am not certain that you will reduce your energy consumption by very much.

@derek-m I don’t really know at this point without doing some experiments. I mean to get myself some openenergymonitor gear, so I could just set the tank stat to 60deg as usual and log the tank temperature for a few days. I should get a good idea of the potential saving, especially with a dumb oil boiler that can’t modulate so has constant oil consumption vs burn time. A reduction in burn time by heating to a lower temperature is a direct oil saving.

Posted by: @cycleneil

@derek-m I don’t really know at this point without doing some experiments. I mean to get myself some openenergymonitor gear, so I could just set the tank stat to 60deg as usual and log the tank temperature for a few days. I should get a good idea of the potential saving, especially with a dumb oil boiler that can’t modulate so has constant oil consumption vs burn time. A reduction in burn time by heating to a lower temperature is a direct oil saving.

I doubt that it would be possible to accurately measure the energy usage, since it will be very much dependent upon the amount of hot water used.

I don't see why it would be difficult to measure energy consumption. It would be the boiler oil consumption rate times the time the oil is being pumped in. I am sure I read of someone on the openenergymonitor forums doing it by putting a power sensor on the power line to the boiler oil pump.