Is immersion heating less water volume than oil?

dohouch · 02-03-2025 05:41AM #1

Does immersion just heat less water ( I think immersion stops at 60⁰C , and oil stops at 80⁰C)

Started using my bath , for muscle relaxation (not washing, I shower first, Japanese custom). If I use electric immersion, set at max temperature, I run out of hot water, but if I use oil I don't. (Have lots of ESSB credit, but it seems that immersion is just heating less of the tank. System is dual circuit, about 5 years old.

Galwayguy35 · 02-03-2025 06:38AM

Immersion gets the water at the top hot but not the whole way down.

I rarely use it, instead I turn on the oil for an hour and have lots of piping hot water.

kirving · 02-03-2025 07:27AM

Yes, the electric immersion heater will generally heat less water.

The below webpage has a pretty good diagram. As electricity generally cost about double what gas did per unit energy, it would be very expensive for the electric element to heat the full water a tank when you don't need all that water very often.

Much of the flow of water around the tank is due to convection, and hot water rises to the top, so if you heat the top portion of the tank, the hot water will stay up there and not really mix with the colder water at the bottom.

https://simplifydiy.com/plumbing-and-heating/hot-water-storage/vented

Markcheese · 02-03-2025 08:43AM

Usually, there are 2 switches on the immersion switch box , and on / off , and a sink / bath one this is because there are 2 heating elements in the water tank , even with that the boiler will usually heat a bigger volume of water -

You should be able to control the boiler so that it only heats the water tank , and not the radiators - - if you want

dohouch · 02-03-2025 08:44AM

@Galwayguy35 @kirving

Seems that way, but our inconsiderate government gave me a giziillion credit on my lecky but refused to divert an oil tanker round to my place, so not wanting to seem ungrateful I thought I should use the lecky, but it just doesn't give enough hot water for a long soak for me 'ol bones. Might be a first world problem 🤔👺

CalamariFritti · 02-03-2025 09:12AM

Think it's due to the coils in the hot water tank. The heating water circuit coil covers more the bottom of the tank typically. The electric coil just covers top half. And with hot water rising to the top the immersion will not get the whole tank heated up whereas the heating circuit will.

As for temperature I dont know what temp immersion typically does, I think its about 60° and the oil boiler typically is set to heat the circuit water up to about the same. @kirving 's diagram explains this perfectly.

John.G · 02-03-2025 01:42PM

https://www.boards.ie/discussion/2058398845/is-immersion-heating-less-water-volume-than-oil

Is your Immersion mounted in the top of the cylinder?, if so, it will normally have two heating elements, one short, the "sink" that heats around 30L, the other, longer, "bath" that heats maybe 2/3rds of the cylinder, depending on its length, have a look at your exising one, there may be some info on it other than just the power in kW. By removing the cover you can check the thermostat setting, normally 60C but can be increased to say 70C which will give a extra 20% equivalent HW but would not recommend this if young children in the house.

dohouch · 02-03-2025 03:56PM

My immediate solution is turn on immersion until it cuts out, I have a current monitor indoors,then use my boiler, dual circuit, until it too cuts out, voila a full tank of hot water, and saved some oil into the bargain. Live on my own and will be doing this twice a week for a soak in water laden with Epsom Salts.

Is immersion heating less water volume than oil?

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