Can a shower be added to my consumer unit?

[DIYNotIan]

Well, I must have not clicked through one of my email notifications because I haven't been getting any for a day or two since starting the thread and so was unaware that it has taken off to a four pager! Some interesting reading indeed.

We have a stream in the garden and apparently cold water is very good for you. I hate it personally, but if I grew to like it somehow then just imagine - all of this could be forgotten about with a load of goosebumps, a touch of hypothermia, and a bottle of phosphate free shower gel

Anyhow, I'll stand back and watch from the sidelines, but I do have a couple of questions...

- How to work out the kW for heating oil, so I can make comparisons between gas and electric (not that gas is an option, but interesting non the less).

- Combi boilers... I thought they had a small tank in them that pre-heated water and kept it constantly hot so as to make it readily available? Am I wrong on that? Or is it just some boilers (or just oil boilers) that do that?

Cheers

 

[winston1]

- Combi boilers... I thought they had a small tank in them that pre-heated water and kept it constantly hot so as to make it readily available? Am I wrong on that? Or is it just some boilers (or just oil boilers) that do that?

Cheers

Indeed, and that rather energy wasting facility can be switched off.

 

[DIYNotIan]

That's good to know. And it can be switched off on all boilers? Gas and oil? Not that I have one, but good to know for future reference....

 

[SUNRAY]

I'm not up to speed with many modern combi's but the only tank in boilers I'm aware of tend to be a pressure vessel, usually painted a bright colour like red or orange and not generally lagged. They will get warm or even hot but that is not the intented application.

There may very well be heat stores in domestic boilers but I'm more familiar with large boilers which are usually basic with the ancilliaries added externally.

 

[BS3036]

That is an expansion vessel, designed to maintain a constant pressure in the pressurised system. The water in the system will occupy one half of the vessel up to the rubber membrane across the middle. The other half typically contains nitrogen under pressure.

 

[flameport]

Standard combi boilers just heat the water on demand. Most have a facility to keep the boiler itself hot, so that when turning on a hot tap, you get hot water more quickly.
If that's turned off, gas is saved but water is wasted as more cold has to be drawn off before the hot arrives at the outlet.

Some combi boilers do contain a certain amount of stored water which is kept hot. Normally used to provide a higher flow rate, as the stored water can be combined with water heated on demand for a certain amount of time. Once the stored hot water is depleted, the flow rate reduces to that of a standard combi.

In terms of efficiency, there is very little difference between a combi and stored hot water in a cylinder. Modern cylinders are well insulated, and will stay hot for days.
The majority of heat losses in hot water systems is from the pipework, and those are the same regardless of whether it's stored hot water or heated on demand.

 

[JohnW2]

- How to work out the kW for heating oil, so I can make comparisons between gas and electric (not that gas is an option, but interesting non the less).

There are various heating oils around, but kerosene works out at about 10.35 kWh per litre.

Kind Regards, John

 

[DIYNotIan]

Thanks John. This kind of maths is really not my strong point!!! So I'm trying to figure out how they would compare. We pay £0.11 per unit for electricity. Kerosene is roughly £0.43 per litre. So for one hour's worth of showering, would anyone care to do the maths?

Cheers

 

[flameport]

Worst case assuming a grossly inefficient poorly maintained oil boiler at 50% efficiency.
1 litre = 10 kWh = 5kWh allowing for losses.

At 43p/litre, that's about 8.6p per kWh, significantly less than electricity.
A newer, more efficient boiler would be considerably cheaper than that.

11p / kWh for electricity is at the very cheap end of the market.

 

[JohnW2]

Thanks John. This kind of maths is really not my strong point!!! So I'm trying to figure out how they would compare. We pay £0.11 per unit for electricity. Kerosene is roughly £0.43 per litre. So for one hour's worth of showering, would anyone care to do the maths?

Flameport did the maths for you whilst I was typing (obviously too slowly!).

The problem with answering your actual question directly is that, as we discovered above, there are fairly dramatic variations in what people regard as acceptable as the flow rate of a shower, which means that there is equally dramatic variation in the amount of water that needs to be heated (hence cost) for a shower of any particular duration.

To give you some idea, a 10.5 kW electric shower (about the biggest one can get) 'running flat out' for a whole hour would use 10.5 kWh of energy (about £1.16 at your {very low} electricity price of 11p/kWh). Using flameport's figures, that same amount of energy (water heating) would cost you about 90p with a 50% efficient oil boiler or about 45p with a hypothetical 100% efficient oil boiler.

However, it seems that those who use mixer showers may expect about three (or more) times the water flow (hence three times the water heating cost) as can be achieved with an electric shower, in which case those figures (for one hour's totally showering) with your 43p/litre oil might rise to at least £2.70 and £1.35, for 50% and 100% efficient boilers respectively.

Kind Regards, John

 

[DIYNotIan]

Thanks @flameport That's what we pay for our electricity (with a standing charge of course). As for the boiler, it's an old Danesmoor 20/25 but I'm sure in it's last service it came in at the high end of the 80s in terms of % efficiency.

 

[DIYNotIan]

And thanks to you too @JohnW2 - that all makes sense.

 

[Harry Bloomfield]

There are various heating oils around, but kerosene works out at about 10.35 kWh per litre.

Kind Regards, John

Interesting, I have never come across any figures. Have you perhaps a figure for diesel?

I have a diesel boiler / night heater gadget in my car, it generates 5.3Kw of heat to warm the engine and cabin up. I have measured it's fuel burn as 0.25L per hour, but that is an hour where it ramps output up and down once up to temperature on it's stat.

 

[JohnW2]

Interesting, I have never come across any figures. Have you perhaps a figure for diesel?

Much the same as kerosene - I think diesel is around 10.0 kWh/litre. However, as flameprt implied, the efficiency of oil-burning boilers can be quite low.

I have a diesel boiler / night heater gadget in my car, it generates 5.3Kw of heat to warm the engine and cabin up. I have measured it's fuel burn as 0.25L per hour, but that is an hour where it ramps output up and down once up to temperature on it's stat.

Per above figure, 0.25 litres/hour would correspond to 2.5 kW, but you would get appreciably less 'usable' heat than that because of the efficiency issue.

I presume that the 5.3 kW figure must be a peak one, modified by a lot of the thermostatic control, given that (due to sub-100% efficiency) the average must be well under the 'theoretical' 2.5 kW.

Kind Regards, John

 

[Harry Bloomfield]

Much the same as kerosene - I think diesel is around 10.0 kWh/litre. However, as flameprt implied, the efficiency of oil-burning boilers can be quite low.
Per above figure, 0.25 litres/hour would correspond to 2.5 kW, but you would get appreciably less 'usable' heat than that because of the efficiency issue.

I presume that the 5.3 kW figure must be a peak one, modified by a lot of the thermostatic control, given that (due to sub-100% efficiency) the average must be well under the 'theoretical' 2.5 kW.

Kind Regards, John

It goes through a modulated series of increasing the level of burn/ output from cold, then gradually modulates back down as it achieves the preset coolant temperature flow (finally cutting out completely at >77C), less than the opening temperature of the radiator stat., at 93C - otherwise it would be burning diesel to heat the coolant and the coolant would be then cooled by the radiator. I guess if it didn't modulate its burn initially, it would flood the combustion chamber with diesel. It sounds like a jet engine when its on. It ignites the diesel/blown air, with a 200w heated pin, which glows bright red when on for several second, until it detects a steady burn.

In normal operation, from cold, heating the coolant in the engine alone, the engine and the cabin heater, before I get in it and start the engine - it will be modulating down within around 20 minutes. With the cabin toasty to get into.