Best way to heat a bath with electricity

[JohnW2]

Do towel baths? The german government was suggesting it when there was gas shortage.

Kind Regards, John

 

[robinbanks]

10KW for 3mins or 3KW immersion for 20 mins... No contest. Even if it heats sufficiently in 20 mins. In 20 mins.

Are you feeling alright?

 

[ericmark]

LPG is likely the best option, a portable cylinder kept outside with a standard central heating boiler. However the size of boiler may be a problem so a narrow boat fuel oil heater

one example given here, does not officially meet the efficiency required for domestic heaters, but they are a lot smaller, it will need a storage tank can't expect instant heating, but much smaller than a normally domestic oil boiler like I use in my house.

The Eberspacher is the most well know, comes as both 12 volt and 24 volt, caravans use a Carver Cascade 2 gas water heater, but the stored water is very limited around 5 gallons, but the canal boat diesel heater does not have a built in tank, so you can select tank size, but more expensive, the Eberspacher tends to be battery powered only for the pumps and ignitors, but the Carver has an electric option so if you run out of gas, you can use electric.

They are designed to vent through side of boat or caravan, the oil one needs a smaller hole to gas option.

Officially neither can be used in the home, as they don't comply with regulations as far as efficiency goes, but are cheaper to run to electric unless using a heat pump.

Boats tend not to use gas, as they in the main need vents under them to ensure no build up of flue gases and drilling a hole in bottom of a boat tends to make them sink, so most boats use oil often same oil as the engine, where caravans can have hole in floor, so tend to use gas which is cheaper.

In the main both use showers not baths, which use less water, the other option is the Irish external immersion heater, the Willis system, by having the immersion heater in a tube, it heats the hot water tank from the top down, so switch on for 5 minutes enough water for sink use, turn on for 3 hours and enough water for a bath, however only Irish plumbers seem to know how to fit them, the pipe work arrangement is critical.

Oil boilers can be fitted outside, in the main oil combi boilers simply have a storage tank in them, the cost of fitting oil boilers is very high, and you need an oil tank of course, I have just refilled mine for the year, around £320 which is just about enough for 12 months with a three story house. The boiler is the size of a kitchen cupboard, plus the flue, they are expensive, but last longer than gas boilers, the gas boilers need a special tank for the LPG gas which is normally supplied by the gas supplier under contract so you can't swap supplier, so gas (LPG) is cheaper to install to oil, but costs more to run, and your tired to supplier.

Using cylinders of gas is possible,

but they draw in heat as the gas is released, so need to be outside and the blue ones can stop releasing gas if it gets too cold. In a caravan I have needed to boil a kettle and pour it over the gas cylinder to get gas. Lucky had a small electric kettle.

Personally I simply don't use a bath, only use showers, seems a lot of effort just to have a bath, the old bath we would fill with the wash tub boiler glad to say those days are gone.

 

[Taylortwocities]

Problem solved.

 

[Harry Bloomfield]

The Eberspacher is the most well know, comes as both 12 volt and 24 volt, caravans use a Carver Cascade 2 gas water heater, but the stored water is very limited around 5 gallons,

Even more limited - the Cascade 2 heats and stores either 6 or 9 Litres of hot water, depending on version.. Perfectly adequate for a quick shower, or to do the washing up.

I think the OP's best solution for speed and economy, is an electric shower, used carefully for an actual shower.

Last time I worked out the cost of a bath, heated by a gas boiler, I think it came in at around 30p. A similar bath of water, heated by electric would be around 3.5x that cost, so around £1.05.

 

[JohnD]

Last time I worked out the cost of a bath, heated by a gas boiler, I think it came in at around 30p. A similar bath of water, heated by electric would be around 3.5x that cost, so around £1.05.

My tariff is unusual, but I pay 5.6 times as much per kWh from electricity as for gas.

I used to run a small electric heater in the bedroom overnight in winter, but it is just as economical now to leave the GCH on, turned low.

 

[JohnD]

For the bath I'm currently using an old immersion tank and heater. But it takes forever to heat up and the bath is not full wasting a ton of energy.

What size is your cylinder, and what colour is it? (This indicates its age, and grade of insulation).

Is the immersion element in the top?

A 3kW immersion heater takes about a minute for each litre of water. If well insulated, it stays hot for a few days. You can probably improve efficiency by better insulation of the cylinder and hot pipes. A bath uses about 100 litres of water, depending how full and how hot you want it. Old iron baths absorb a huge amount of heat.

In a previous home I had a multifuel boiler, which burned wood or smokeless fuel, and as well as heating the living room, heated a bedroom radiator, towel rail and a hot water cylinder, on gravity circulation. I could damp it down to burn all night with the smokeless fuel.

 

[ericmark]

I have a 2 bed bungalow electric only, no gas in the area.

I live where there is no piped gas, but loads of people use LPG or oil. My oil boiler is 20 kW, and heart of winter runs around ¾ of the time, so for electric looking at about the same or more to be able to switch off, then back on again when needed, don't want to run it 24/7 so the larger it is, the less time to re-heat the home.

20 kW = 86 amp, and my incoming supply is 60 amp, OK a heat pump may need less, but if I consider 40 amp for a shower, then I have 20 amp to spare, so 4.6 kW, maths shows it is simply not going to be enough. OK not a bungalow, it is a three story house, but electric heating is a non starter.

I have loads of wood in stock, and an open hearth, but that is really bad for the environment with particular emissions etc. So best for environment as it stands is still fossil fuels, to think we can change in less than 100 years is living in cloud cuckoo land, it took over 100 years to get us all on the national grid as it stands, so history shows us how long it will take.

OK new builds with energy storage great, but to convert, one needs to get real.

 

[robinbanks]

OK a heat pump may need less

About 4 kW for my 12kW HP

to think we can change in less than 100 years

I don't think it will take as long to repurpose an infrastructure as to develop it initially..

 

[ericmark]

About 4 kW for my 12kW HP

So for my house looking at 8 kW or around half of the total supply to house, so not going to work. Same applies to electric vehicles.

 

[JohnW2]

I have a 2 bed bungalow electric only, no gas in the area. I have an electric shower and 2 tankless electric water heaters for the bathroom and kitchen sinks. For the bath I'm currently using an old immersion tank and heater. But it takes forever to heat up and the bath is not full wasting a ton of energy.

As has been said, to have baths (rather than showers) if one is reliant on electrical heating of water is an expensive luxury.

However, in relation to what you say above, I'm not sure what the problem is. In terms of your baths, you are in exactly thee same situation as the millions of people who use 'stored' hot water - whether it is heated by electricity, natural gas, LPG, oil or whatever.

In such a situation, one does not turn the water heating on ('from cold') immediately before one wants to take a bath - one heats up the water in the cylinder long before that - so that it is immediately available to fill a bath (as fast as the pipework and height of 'water head' {or pressure} will allow) when needed.

The common situation is that in which people want hot water to always be available (not just for baths), so their system is arranged such that the cylinder is always full of fairly hot water. However, if you want the cylinder only for filling baths, then you would simply need to switch the immersion on, say, 3 or more hours before you intend to take a bath (using a time switch to do that if necessary).

Kind Regards, Jophn

 

[robinbanks]

So for my house looking at 8 kW or around half of the total supply to house, so not going to work. Same applies to electric vehicles.

If you've determined your house needs heat input of 24kW then yep, that ASHP would usually have an 8kW draw.. But 24kW is massive in HP terms - you'd be better off embarking on a comprehensive upgrade of your insulation and draftproofing to reduce the demand, not fitting a massive heat producer to overcome a large loss

 

[JohnD]

...The common situation is that in which people want hot water to always be available (not just for baths), so their system is arranged such that the cylinder is always full of fairly hot water. However, if you want the cylinder only for filling baths, then you would simply need to switch the immersion on, say, 3 or more hours before you intend to take a bath (using a time switch to do that if necessary)....

If you have very good insulation of the cylinder and pipes, the timing is not very important. The thermostat will turn off the element once the water reaches your target temperature (unless it is faulty, in which case it must be replaced). A timer will save you money if you have a time-related source of cheap electricity, such as Solar power or Economy 7.

 

[JohnD]

I have loads of wood in stock, and an open hearth, but that is really bad for the environment with particular emissions etc.

Save up for a clean-burning, efficient Multifuel stove.

 

[JohnW2]

If you have very good insulation of the cylinder and pipes, the timing is not very important. The thermostat will turn off the element once the water reaches your target temperature (unless it is faulty, in which case it must be replaced). A timer will save you money if you have a time-related source of cheap electricity, such as Solar power or Economy 7.

All true. The point I was making was that, in the apparent (unusual) case of thee OP wanting immersion-heated water for baths, then, even if his cylinder were fairly poorly insulated, if he switched it on, say, 3 hours before a bath was required (with a times witch, if, for example, he would be asleep at that time) (and then turn it off when he had his bath), then heat loss would be pretty low.

However, you're certainly right that a "very-well-insulated" cylinder will retain it's heat for a long time, so for most people it's quite reasonable to leave it 'powered' continuously (or continuously during cheap-rate hours, if one has a dual-tariff supply such as E7), leaving the thermostat to only power the element when required for 'top-ups'.

I've posted this before (so not up-to-date). In my case (with 'very good insulation' - see below) , since I have E7, the immersion circuit is only powered during the seven nocturnal 'cheap hours'. When first energised (about 00:30 GMT) the element is powered, usually for 1.5 - 2.5 hours, to get it 'up to temp' before the thermostat switches it off, after which there are just occasional very brief periods of 'top-up' (mediated by thee thermostat) during the rest of the night. By 00:30 GMT the next day, some 22 hours after the end of the last 'main burst' of heating, and some 17 hours after any immersion heating, thee water is still plenty hot enough.

However, to achieve that sort of performance really does need "very good insulation". I've also posted this before ... My HW cylinder is in a relatively little heated part of the house, such that heat loss shows considerable seasonal variation. In May 2018, I upgraded the 'supplementary insulation' (in addition to that on the cylinder itself) from about 200 mm (top, bottom and sides of cylinder) to some 400 - 600 mm, and that resulted in something like a 2-3 kWh/day per day reduction in energy usage.

However, this does illustrate that, despite what some people believe, even an extremely well-insulated cylinder can loose significant heat if in a fairly cool environment. This graph illustrates the dependence on immersion energy usage (hence heat loss) on variation in (ambient outdoor) mean temperature during the year. The effect of thee increase in insulation in May 2018 is again very apparent. ...

Kind Regards, John