[wizzo227]

This winter I'm trying a different tactic for eco friendly hot water.

A plain over-the-basin electric water heater.
Theory is that the gas combi boiler is so rarely used that to wash hands upstairs, requiring warming up the whole boiler, then the full length of the pipe run, burns a lot more heat than gets used to wash hands upstairs.

So I bought an over-the basin hot water thingy, with an insulated small (five litre) capacity and 2.2kW electric heater element. 1960's clicky thermostat technology, with improved insulation design claimed to need very little energy to keep it up at hot water temperature.

What would you like tested ?

[geoffers]

@wizzo227 I had a similar plan earlier this year --- since I've got an electric shower and dish-washer (my water is heated with a regular boiler/hot-water cylinder) it seemed excessive to heat the tank just for a bit of hand washing and the occasional dish washing (could use the kettle for this), so I turned off the water heating via the gas boiler.

However with a bit of testing I calculated that I could use the immersion-heater controlled by a "smart" switch to use some of my cheap-rate overnight Next Drive tariff to get the tank warm enough for a day's general usage, more cheaply than by using the gas boiler to achieve the same water temperature.

One unexpected observation which came out of this testing that could possibly prove costly... I had the tank thermostat set to the recommended 50⁰C, but since the weather was relatively mild had turned the boiler supply water temperature down. This meant that the supply temperature was not enough for the tank to actually reach the temperature to turn the tank thermostat off, so the boiler would have kept cycling on/off all day trying to get the tank up to temperature.

So its actually sensible to keep the boiler supply water temperature up - the radiators will be hotter, but since radiators are controlled by thermostatic valves and a house thermostat, the room temperatures will be reached quicker so the thermostats will shut down sooner.

[meldrewreborn]

@wizzo227

with gas one quarter the price of electricity for most of us, I’d not even consider this.

heat losses from pipe work will not really be wasted as it will add to home heating in the winter period, but that would not be wanted in the summer.

and the key factor would be how long for any running cost savings to offset the capital cost.

[Andy65]

@wizzo227

If the upstairs basin is used solely used for washing hands (I think in reality it probably isn't), then I'd just wash my hands with cold water. I nearly always use cold water if it's just for washing hands.

Are you going to do a true cost comparison, washing hands with hot water from the boiler versus your water heater?
The boiler will use a bit of leccy so that has to be included, how much was your water heater?

If you include the cost of the heater, I would guess that the boiler is the cheaper option over a reasonable period of time, say 5 to 8 years.
It also depends on where your boiler is installed compared to the bathroom, mine is next to my bathroom so the pipe run is about as short as you can get.

[wizzo227]

@Andy65

All gas and fossil fuel boilers fail on cost of running at nil net carbon, with nobody even close to a scaleable carbon capture and storage solution to gobble up more than all pollution from oil and gas. I do not seek minimum cost because I don't disregard the pollution.

The old gas combi boiler is downstairs in the kitchen. It is several minutes x 15kW of gas to start getting hot water upstairs, so I do that for a bath or might use a kettle to wash hands. My normally-off gas boiler using 120 Watts for a few minutes for pump and blower doesn't impair my costs and in daytime can often do that inside the free solar power surplus.

The new water heater, being less than £90 new, is just a component for some smart appliance design-test-improve pokes. It is a well insulated 5 litre capacity thing containing a 2.2kW water heater element, a spout, and a mechanical thermostat which I'll still want as a safety limit. In some respects I could have saved the money and tested with a kettle or with a smaller water heater, but that would have lacked capacity and insulation by comparison to what I''l need to catch the available sporadic little bits and pieces of cut price electricity, always seeking more utility within genuine nil CO_2.

I'm not aiming to beat "mines cheaper than yours" metrics this time, which the £5 kettle last year was the winner of, and the £15 half-size kettle was getting best matching to available free solar in summer enough to have fully paid for itself and then continues to make gainful savings. I am aiming towards "if new-build houses got these instead of gas combi, that would best do the job for them, at nil net CO_2?". I looked at "solar diverter" immersion heater hot water tanks, and thought that those look a lot bigger than the quantity which I'd use or the solar power surplus which I'll have off my small roof this winter. I've already spent an extra £40 on a suitable 220/110 Volt transformer because the roof more frequently has 600 Watts to spare than 2000+; this is a test&dev project not a final product, for which a family sized hot water tank and much bigger rooftop solar should probably be better. Minimum cost could build a water heater like mine with a smaller 240 Volt heating element.

[wizzo227]

@geoffers
Is there any product on the market by which you could set your hot water tank thermostat to seek 65C+ legionella-killing temperature during the 7p/kWh night rate times, and then relax that back to something careless and much lower during expensive daytimes, expecting insulation to let that drop back to perhaps 50C? Have you considered household policy such as "Tuesdays are always Bath days" to only need any tank heating quite occasionally the night before? If you have the 1990's arrangement whereby a normally-on gas combi sends much heat to the water tank, have you considered criteria by which you'd decide to switch the gas to hard OFF for a couple of days ? It is the wrong time of year to do that now, but I'm down to six minutes per day of gas burner on, soon to go up a bit for winter.

[Andy65]

@wizzo227

I don't fully understand where you're going with this. If you are offsetting the electricity used by the boiler from solar, then somewhere along the lines you need to include the cost of your solar/battery installation.

Your original post was "Theory is that the gas combi boiler is so rarely used that to wash hands upstairs, requiring warming up the whole boiler, then the full length of the pipe run, burns a lot more heat than gets used to wash hands upstairs."

My question was simply are you going to calculate whether it's actually cheaper or not. If you're saying it takes 'several minutes' to get hot water upstairs then I think you maybe need to look at your boiler.

Net carbon etc is a load of guff quite frankly. So what will it cost to heat 5 litres of water, to say 60C, with your 2.2 kW heater?

[geoffers]

@wizzo227 - I haven't looked for any programmable tank thermostats, but in today's era of smart devices I'm sure that could well be something that's available.

I did do quite a lot of reading regarding legionella and came to the conclusion it's one of those things which is a big worry about nothing much.

It sounds more of a issue in large premises (hospitals; apartments; refugee barges etc), but the number of instances of household infection are minimal though potentially still possible.

I'm sure it's one of those things blown up by the media's "bad-news-is-good-news" reports, so I guess it all depends on your attitude to risk.

Apparently if you make sure you do heat the tank up to greater than 50⁰C fairly regularly (eg weekly bath rather than shower) you should zap any blighters which may be lurking.

[wizzo227]

I might look at the cheaper/not cheaper after I've run it a few times for averaging. I really don't like to base decisions on £ but since most other people do, yes I'll work it out carefully.

Because I've had solar on the roof for more than ten years which has more than fully paid for it, ongoing cost to use solar a bit more is literally nil and capital cost is now literally nil. I'm also going to try to keep an eye on electricity costs at night time and in horrible weather; I won't always get free hot water from this. The 7p/kWh night rate looks like a good minimum-£ deal.

I confirm that it is the normally-off-ness of the boiler and pipe run which adds minutes to the time to get hot water upstairs from it. I could just switch it back to normally-on circulating hot on thermostat, and decrease by three minutes the time to get hot upstairs to the same as my neighbour, but at nil net carbon the cost of carbon capture and disposal for that much gas would be prohibitive, so I'd rather not do what most people presently do.

Whoever said that net carbon is guff, I'm not going to agree with you and I do not pretend to. I'd prefer to be wrong than be hit by climate change, but has anyone noticed anything off about the weather in the past decade by comparison to previous decades ? I continue to seek methods which work, and if they'll save money too then there is better chance of mainstream acceptance of improved methods.

[meldrewreborn]

I firmly believe climate change is real, and I further believe we as a nation could do more to move to net zero more quickly.

perhaps selfishly, I also think it’s our government’s job to implement the changes to our infrastructure and set the economic condition appropriately to encourage the populace to adopt energy that uses low carbon sources.
on the home front, I’ve considered solar panels, remember part of my roof already has solar thermal, and concluded that it’s not cost effective. I’ve also thought of using battery storage fed by less expensive night time electricity. Again it was not cost effective. Replacing my gas boiler with a modern more efficient model - same story! And fitting an electric heat pump - again not cost effective.

Now if gas were more expensive and electricity cheaper (think shifting “green taxes” from electricity to gas for a start, perhaps raising VAT on gas) then the balance of advantage would inevitably change, and gradual rather than overnight change is what is needed.

But I’ll not go down the ECO route unless it is to my advantage. I’ve a hybrid car, loft and cavity wall insulation (since 1988), double glazing and good heating controls. I think I’m doing my bit, but readily recognise that some want to do more, and there are those who want us all to do more (whether they do themselves what they call upon us to do is another matter).
But governments set the rules and we live within them, and we also elect the governments. The rules apply to all of us equally, and how we react rule changes will differ from one household to another. That is sensible and logical and fair.