Moving from a property with combi boiler to electric immersion

macman

The long term solution is to replace the convectors with NSH's and switch the metering to E7. It's unlikely that E7 will work if it's only used for DHW.

throughtheblue

Alnat1 said:

My simple non-expert thoughts - Heating a certain amount of water from one temperature to another will take the same kW of energy whatever fuel. A boiler is less efficient than direct electric heating so will use slightly more.

We use our gas boiler to heat our 160l tank (modern, well insulated, feels only slightly warm to touch) for 40 minutes each morning. Tank temp is set to 50C as is boiler. This gives us enough hot water for 2 morning showers, hubby's shave and a bit left over for cleaning etc. If we need more we can boil a kettle, although not had to yet.

This uses under 3kWh of gas a day, might have to put up boiler temp a bit in winter when incoming water will be colder, so perhaps 4kWh. We rarely have baths but can put it on boost manually for 15 minutes extra and get enough for a medium depth bath.

Hope this helps you see that hot water tanks aren't so bad if used efficiently.

Can you see if my understanding of energy loss from the electric immersion is roughly correct.

It takes 2 hours to heat a full tank of water (6KW). If the tank lost 2kw over 24 hours, would we need the immersion on for roughly 1 hour per 24 hours to replenish that? (maybe 30 mins in the morning, followed by 30 mins in the evening).

I'm aware a lot comes into it like the amount of water used from the tank, and the temperature dropped. We plan on only using the water in the immersion for showers, so maybe 30l per day.

matelodave

You will reduce the heat loss from the tank by reducing the temperature of the stored water, adding extra insulation (both to the tank and to the surrounding pipework. 

As I said above we get away with a tank temp at 45 degrees which means we dont have to add cold water to the hot, either when showering or washing in fact I can easily wash my hair direct under the hot water tap.

We've fitted flow restrictors to the taps which reduces the amount of water that gets wasted down the sink, although it does take a bit longer to fill a basin or sink. We don't have a bath, just a shower which again is limited to 6 litres a minute (we've got an EcoCamel shower head which I liberated from out caravan.  As we've got a heatpump we can reheat our tank in less than an hour using just over 1kwh of leccy in the summer and a around 2kwh in the winter.

You can use the calculator here to work out how much energy you need and how much time it takes and the size of your immersion - https://bloglocation.com/art/water-heating-calculator-for-time-energy-power (dont forget to change the temp to degrees C and the volume to litres)

markin

throughtheblue said:

QrizB said:

Does your EPC also give an annual energy demand in kWh?

Current Flat, electricity with Combi boiler for water and heat = 302 kWh/m2/year

New House, just electric = 452 kWh/m2/year

But we can significantly reduce the main expense of heating by using the log burner. We'd plan on buying enough fuel for 5/6 months of the year.

452 kWh/m2/year, I think would usually be an high E or F property, So its wrong or your underestimating of usage is.
 

Reed_Richards

Yes, are you sure it isn't 45.2 kWh/m2/year?  452 is half as much again as your flat  (302) and presumably the house has a greater area so more m2 in total.

throughtheblue

Reed_Richards said:

Yes, are you sure it isn't 45.2 kWh/m2/year?  452 is half as much again as your flat  (302) and presumably the house has a greater area so more m2 in total.

The flat is 66m2

The house is 61m2

Our flat is a 2 bed, with a very large lounge, and 2 double bedrooms, but has a lot of inherited furniture that takes up space.

throughtheblue

markin said:

throughtheblue said:

QrizB said:

Does your EPC also give an annual energy demand in kWh?

Current Flat, electricity with Combi boiler for water and heat = 302 kWh/m2/year

New House, just electric = 452 kWh/m2/year

But we can significantly reduce the main expense of heating by using the log burner. We'd plan on buying enough fuel for 5/6 months of the year.

452 kWh/m2/year, I think would usually be an high E or F property, So its wrong or your underestimating of usage is.
 

It's an E with a potential of A in both lower running costs and lower CO2 emissions.

Walls, roof, windows, floor are all 5/4 stars. Main heating, mains control and hot water are all 1 star based on no mains heating, electric heaters and electric immersion. It's not quite a passive house, but once injecting a bit of heat (1 hour) it rarely needs much more. A log burner is also being installed free of charge, so I will be using this as primary heat. 

Reed_Richards

You used to have a gas combi boiler heating your flat and you are moving to an-all electric house of a very similar floor area but with a heating requirement half as much again as your flat per suare meter.  Electricity is about 3 times as expensive as gas.  Without your log burner expect your heating bills to be 1.5 x 3 = 4.5 times greater than they would become for your flat in October.

I think you are letting a brief impression of the new house in winter blind you to the fact that the numbers say it is badly insulated.

Passive House requirements

For a building to be considered a Passive House, it must meet the following criteria ( for detailed criteria, please see the building certification section):

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

That's 15 kWh/m2/year for a Passive House compared to your 452 kWh/m2/year!!!!! 

QrizB

throughtheblue said:

Reed_Richards said:

Yes, are you sure it isn't 45.2 kWh/m2/year?  452 is half as much again as your flat  (302) and presumably the house has a greater area so more m2 in total.

The flat is 66m2

The house is 61m2

61m2 at 452kWh/m2/yr makes 27572kWh/yr. If correct, at the expected tariff of 34p/kWh that will cost around £9400/yr.

I could be very wrong here, of course.

throughtheblue

Reed_Richards said:

You used to have a gas combi boiler heating your flat and you are moving to an-all electric house of a very similar floor area but with a heating requirement half as much again as your flat per suare meter.  Electricity is about 3 times as expensive as gas.  Without your log burner expect your heating bills to be 1.5 x 3 = 4.5 times greater than they would become for your flat in October.

I think you are letting a brief impression of the new house in winter blind you to the fact that the numbers say it is badly insulated.

Passive House requirements

For a building to be considered a Passive House, it must meet the following criteria ( for detailed criteria, please see the building certification section):

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

That's 15 kWh/m2/year for a Passive House compared to your 452 kWh/m2/year!!!!! 

Interestingly enough, the EPC rating is being disputed due to over emphasis on the electric heating, when the level of insulation used in the property was designed to use little heating. The chartered surveyor is in agreement, and said there was an overhaul of the EPC data/background calculations undertaken by Energy Action Scotland and many changes have been made, and their working on calculation changes for the future.

Disclaimer: I don't know a lot about this, other than being made aware about discontent regarding the EPC.

From my experience, I stayed in March for a few days. One evening, the temperature dropped to 2 degrees, I didn't actually feel that chilly but decided to put the electric heater on before bed for maybe an hour. I ended up needing to open the window whilst trying to sleep as I was too hot.

Another small help is no standing charge on gas, as well as no standing charge on electricity as agreed with the landlord.