Heating water electrically

[ban-all-sheds]

I was talking about desirable DHW temperature, not the output temperature of a shower.

No you weren't:

that would have only got you up to 41.9°, only slightly above body temperature and therefore probably wouldn't feel even warm, let alone hot, to the touch.

 

[JohnW2]

I was talking about desirable DHW temperature, not the output temperature of a shower.

No you weren't:

that would have only got you up to 41.9°, only slightly above body temperature and therefore probably wouldn't feel even warm, let alone hot, to the touch.

Yes, you're probably pedantically correct in terms of that actual comment I quoted, but (although I may be wrong) I still don't think that most people would regard 40° (or 41.9°) as particularly hot. However, the discussion in this thread is about a request to replace an immersion heater by some sort of instantaneous water heater (i.e. for all DHW needs), so most of my comments have related to that bigger picture.

Kind Regards, John.

 

[ban-all-sheds]

Yes, you're probably pedantically correct in terms of that actual comment I quoted, but (although I may be wrong) I still don't think that most people would regard 40° (or 41.9°) as particularly hot.

Like I say - measure yours. (oo-err, missus)

I find 40° fine - it doesn't make me wince, nor wish for more. I'll try 42°, and report back.

However, the discussion in this thread is about a request to replace an immersion heater by some sort of instantaneous water heater (i.e. for all DHW needs), so most of my comments have related to that bigger picture.

For general purpose DHW you would want more - with a pair of Marigolds on and a pan with the residue from last nights green Thai curry to shift you could tolerate and need hotter, and then there's the flow rate for bath filling and showers.

I get about 50° at the shower head, and that is too hot for use. Haven't measured what it is at kitchen or bath taps.

So let's say you want a nice deep hot bath, for a long soak. You're going to mix some cold in it to the point where you can get in and lie there and be OK as long as you don't move about to much in the first 10 minutes.

200l of 50-odd° water, which we'll say is a Δ of 40° in the depths of winter, and lets say you want to be able to fill your bath in 5 minutes.

I make that a requirement for an instant heating appliance of 111.7kW.



It's never going to work for a bath, is it.

 

[ban-all-sheds]

Also, when thinking about shower temperature, if you are heating the water generally rather than running an electric shower, the DHW supply needs to be considerably hotter than the shower setpoint for the thermostatic valve to work. Some of the better valves will work with only 5˚C, others need as much as 10˚C - so for a 40˚ shower the DHW would need to be at least 50˚. If the DHW temperature isn't high enough, then the shower won't shut off on loss of cold supply.

Interesting and useful info - I've been thinking about getting a thermostatic mixer, so I'll watch out for that - thanks.

 

[JohnW2]

For general purpose DHW you would want more - with a pair of Marigolds on and a pan with the residue from last nights green Thai curry to shift you could tolerate and need hotter, and then there's the flow rate for bath filling and showers.

Indeed so.

I get about 50° at the shower head, and that is too hot for use. Haven't measured what it is at kitchen or bath taps.

Are we talking about 'instantaneously heated' water here? With stored water, of course, there is the consideration that storing hot water at less than 60° is not considered bacteriologically safe (particularly in relation to Legionella) - so, unless one has appreciable heat loss in long pipe runs, or thermostatic mixer supplies to the hot taps (which is what some recommend for bath taps), one's hot tap water is then likely to be well above 50°.

...I make that a requirement for an instant heating appliance of 111.7kW. It's never going to work for a bath, is it.

Not very well, no. However, I imagine that, like me, you know people who do run baths from fairly modest-sized combi boilers (I have family members who do) - I can but presume that they have shallow baths, cold baths or else or are very patient in waiting for their bath to fill!

Kind Regards, John.

 

[ban-all-sheds]

Are we talking about 'instantaneously heated' water here?

Yes, of course.