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In the summer, we only use our central heating to heat the domestic hot water. Has anyone looked in to the economics of using the immersion heater during the Octopus Go cheap rate period instead of using the gas boiler?
 

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At 5p kWh it isn't going to save money vs. an efficient gas boiler, but depending on grid intensity it could be less CO2.

We were on Agile for a while and I did use immersion when price was low. Some Agile users have got smart controls to do it automatically.
 

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Considering that most people on mains gas wont pay more than 4p per kWh I suspect it won’t make any economic sense unless you were using a heat pump rather than an immersion heater but even then I suspect it wouldn’t make a significant difference either way when all your doing is heating a bit of water for a few hours. Would be an interesting intellectual experiment though as everyone loves a good bit of empirical data!
 

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I suspect it won’t make any economic sense unless you were using a heat pump rather than an immersion heater
We installed a hybrid heat pump water heater in Florida and they are taking over there from solar thermal due to lower install costs. Incredibly cheap to run in the warm climate there!
 

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MG ZS EV
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I'm not sure that gas is cheaper.... how much heat is lost to warming up the boiler and the volume of water passing round the loop and any losses in poorly lagged pipework. I have an oil system, I hear you say oil is expensive.. you won't hear oil burning households complain these days... but by the time I have heated a huge chunk of metal and over 30 litres of water in a 28mm pipe circuit I won't burn oil in the summer even at 3p a kWh. Last year I bought at 1.7p a kWh and whilst the price is higher now c 3.8p kWh there is only a small difference in the fraction between Jet fuel and domestic kerosene, and there isn't a great demand for the former at the moment. Of course, it is on my conscience that my heating system produces so much CO2, hence my investigation into a heat pump. Go or Go+ with a cheap overnight tariff could offer heat at less than 2p a kWh.
 

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There is also the re-heat times to concider. Most hot water tanks have a 3kW immersion element. If its running for 5 hours, you can heat 257 litres in that time from 10C to 60C. If its the 4 hour Go tariff, then around 205 litres of water can be heated from 10C to 60C in that time. If you have a 300 litre tank or are a heavy user of water, you might find that you need a top-up of heat during peak rates. What makes more sense is to allow a heat pump to heat that tank of water during off-peak times. Even if the CoP of an ASHP reheating hot water in the depths of winter is say 1.5, that's still better than an immersion.

You can also get an unvented hot water tank, with a mini air source heat pump strapped to the top of it, air ducted in and out. Many of those are slower to re-heat however, so are probably better suited to flat rate tariffs as they'll tend to want to top up the tank with just a 3k drop in tank temperature in many instances.
 

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I'm not sure that gas is cheaper.... how much heat is lost to warming up the boiler and the volume of water passing round the loop and any losses in poorly lagged pipework. I have an oil system, I hear you say oil is expensive.. you won't hear oil burning households complain these days... but by the time I have heated a huge chunk of metal and over 30 litres of water in a 28mm pipe circuit I won't burn oil in the summer even at 3p a kWh. Last year I bought at 1.7p a kWh and whilst the price is higher now c 3.8p kWh there is only a small difference in the fraction between Jet fuel and domestic kerosene, and there isn't a great demand for the former at the moment. Of course, it is on my conscience that my heating system produces so much CO2, hence my investigation into a heat pump. Go or Go+ with a cheap overnight tariff could offer heat at less than 2p a kWh.
So do you use electric immersion over the summer? It's doable I suppose if you only need one tank heated overnight and are on a cheap overnight rate, but is swings and roundabouts as you pay more for your day rate on all those tariffs.
I get there are pipe losses in using a boiler, but equally there are losses in heating water at 6am that you might not use until 9pm. Haven't a clue which is the greater though, but I'd still wager oil at 4p per kWh would still be cheaper than electric at 12p?
 

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The economics of immersion vs gas boiler depends on the installation and your consumption.
I have had a new gas boiler installed along with a new 250 litre HW tank ( Megaflo 250DD ) with 2 immersions that can be powered by my solar system and Go etc .i.e. I have removed the gas water heating.
If you have an old boiler (over 10 years old ) or a long pipe run from the HW tank to the boiler then GO may well be cheaper. If your tank is small and poorly insulated you may run out of HW during the day.
Overnight GO electric will be much lower carbon than gas, but you can run a trial of both methods, with a smart meter you can measure your consumption of gas and electricity easily and do the calcs for your particular circumstances.


If you do run HW just on electricity I'd recommend you use the gas boiler once a month to exercise the diverter valve and pump, if these seize through not being used it will negate any savings !
 

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But Go can be a false economy, as you are paying more for all your peak electric. No point saving 30p overnight if your day time cost is 40p more than it would be on another tariff. So even if you are on Go at 5p and ignoring those factors it's probably very marginal as to whether immersion Vs gas is better.
We are on oil so it is pretty impossible to measure anyway, other than maybe time how long the boiler is firing and measuring the water temp (it's gravity fed too, which may or may not be better for efficiency - no pumping needed but presume some additional losses as heat from the tank moves through the gravity loop, though most of the boiler heat should find its way into the tank eventually).
It should be lower carbon though, I agree, as long as the wind is blowing, but if fossil fuel generation is above around 40/50%, it won't necessarily always be, due to generation and transmission losses etc.
 

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So do you use electric immersion over the summer? It's doable I suppose if you only need one tank heated overnight and are on a cheap overnight rate, but is swings and roundabouts as you pay more for your day rate on all those tariffs.
I get there are pipe losses in using a boiler, but equally there are losses in heating water at 6am that you might not use until 9pm. Haven't a clue which is the greater though, but I'd still wager oil at 4p per kWh would still be cheaper than electric at 12p?
I use the immersion when the heating system isn’t in use. We have a 160 litre hwc so 5 or 6 kWh gives us a tankful. And despite having 3 bathrooms currently there are just 2 of us rattling round the place. The tank is well insulated and holds the heat all day. We use a dishwasher and a washing machine which are cold fill. So the thermostat on the immersion heater is set high and supplies bath and a shower each evening. We do have one unusual feature which is a pumped hot water circulation system to feed the kitchen, utility room and 2 showers. That can quickly reduce the temperature but not many households will have one. If I have some washing up to do, baking tins etc, I’ll boil a kettle to top up tepid hot water later in the evening. When the heat pump is installed we will have a 300 litre cylinder heated by a 12 to 14 kW heat pump. We also have a large kitchen with underfloor heating. The heat pump is likely to be pressed into heating that through the night, which will demand about 6 kw. Sadly I sometimes st by the boiler with a stopwatch measuring demand of the heating system!

Nice that I can admit to being a sad old man amongst friends here!
 

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It's surprising how many people have hot water tanks rather than on demand hot water. We have the latter and use around 1750kWh of gas for hot water each year. I know that there is some wastage while waiting for it to run through hot, but that seems minimal compared to heating a massive tank every day which may not be needed.
 

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Certainly, a mate of mine uses Octopus Go to heat water with the immersion. He finds it preferable to the biomass boiler.

When I was on Octopus Agile I used a Shelly 1 PM linked to IFTTT to heat the hot water tank if the electricity was below the cost of mains gas.

Cheers
 

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Hot water tanks are on the way back because of the way we are starting to think about energy. Sure, smaller houses can have a gas boiler with on demand but after 3 bedrooms 1 bath and kitchen, things get more difficult. We’re replacing our 14 year old system boiler with a heat pump in a few months which comes with a 200l hot water tank. This is mainly because how this technology works but if we swapped it for a new boiler, it would need a tank anyway as the system boiler wouldn’t be able to cope with the demand for the house so the tank would be needed to supplement the boiler anyway.
 

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But Go can be a false economy, as you are paying more for all your peak electric
I could not find a reputable supplier who offered a standard tariff for much less than the Octopus Go day rate we were paying. Have you?
 

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I could not find a reputable supplier who offered a standard tariff for much less than the Octopus Go day rate we were paying. Have you?
Been paying less than than 11p a kWh with Symbio energy for several years now. Octopus is around 14-15p in my area at least, which is pretty average.
 

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The energy trust did tests on modern condensing gas boilers about 28 in in houses in actual use.

In the non heating season and with a storage tank they showed it is virtually impossible to achieve > 50% efficiency (energy in v energy out) and those who use less water more like 35%
 

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I heat my water via Go rather than using the gas boiler. It works reasonably well. I fitted a 7 day timer switch to control the immersion heater. I reasoned that a boiler heating water to 60 degrees is probably less than 75% efficient and at that price it's comparable to the Go tariff. As the immersion heater is in the tank there isn't the loss through un-insulated pipes. My only issue is that my tank has a top mounted immersion heater. It's great if it ever needs changing as you don't have to drain the whole tank down but even with an extra long heater element it only heats the top half of the tank. The central heating coil is about a third of the way up and there is a bottom solar panel heating coil which I've never used. It was my intention to fit a solar water heating panel, but we had a loft extension built on the south side of the roof which stopped me doing so.
 
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