'tis but a few minutes work to calculate how long a 3kW (max) heater will take to raise Xl of water from Y°C to Z°C assuming no losses.
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- Thread starter ebberz
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I would imagine there are great losses having Xl of water in basically a huge bath covered with a bit of expanding foam outside 24/7
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Hopefully if someone was spending 4 grand on a hot tub they would not consider just plugging it in.
On the other hand, the product details include this:
so anything is possible.
On the other hand, the product details include this:
so anything is possible.
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Well, I worked out an example to see what ballpark it's in...
800 litres, from 15° to 37° (just picked because it's body temp), with a 2kw heater, would take 10.2 hours!!
With real world losses, it's not going to be quite what people had hoped for!
Don't some of these people with more money than sense leave them switched on more-or-less continuously? If so, they would presumably not be too concerned about the initial heat-up time.
To be fair, if they do sell some hot tubs with 13A plugs, they are probably pushing that plug to its limit - so you probably should have calculated on the basis of 3kW (i.e. about 6.8 hours).
Mind you, I recall that in my grandparents' house, if anyone wanted a bath, the coal fire/boiler had to be fired up, followed by a wait of a good few hours before there was a tank full of hot water at a usable temp - so maybe they wouldn't have been too shocked by 6.8 or 10.2 hours!
Kind Regards, John
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Both the models mentioned have a 2kW heater.
Proper hot tubs are designed to be left on 24/7, but they have decent amounts of insulation in the sides/base and a very thick insulated lid.
That makes sense. If they are well insulated (and used reasonably often) it might even be more cost-effective to leave them on 2/7 (a bit like the decades-old immersion heater debate!).
Kind Regards, John
It is never more cost effective to leave anything on 24/7. Maximum losses are at the working temperature. Any period at a lower temperature, however short, will result in less overall losses.
So they're a warm bacterial stew of exfoliated skin, hair, grease, grime and bodily fluids.
That does, indeed, seem 'obvious' - but, as I said, there have been decades of debate about this (in relation to domestic immersion heaters), amongst people who are not all totally daft - although I can't currently recall the various arguments.
I think that one of the variables is the question of what one is trying to achieve. Those who want the water always to be close to 'working temperature' will be switching it on whenever the temperature falls a little, thereby more-or-less emulating what the thermostat would be doing if they left it always switched on. If the human being had less 'hysteresis' than the thermostat, I suppose that could result in an increased energy usage.
Kind Regards, John
ISTR that the rate of heat loss, or transfer from A to B, is proportional to the gradient between A&B.
If so surely a cylinder of hot water will lose more heat if kept at a high temperature than if it is allowed to cool?
If so surely a cylinder of hot water will lose more heat if kept at a high temperature than if it is allowed to cool?
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