New house with Combi boiler - hot water is SO much higher than old house with system heating, why?

Zandoni

Don't use the hot tap to wash your hands, they are usually done before the heat gets through.

victor2

Zandoni said:

Don't use the hot tap to wash your hands, they are usually done before the heat gets through.

That's certainly the case for us in the kitchen - boiler is downstairs near the kitchen but pipe run goes upstairs to where the hot tank used to be then down to the kitchen. Takes forever to warm up!

Reed_Richards

Zandoni said:

Don't use the hot tap to wash your hands, they are usually done before the heat gets through.

I have a system the circulates hot water from the cylinder round a loop and back to the cylinder.  All the hot taps run off this loop.  I run the recirculation pump for 5 minutes an hour (on a timer) whilst we are awake.  This is not a money saving option, but it does ensure that warm or hot water comes promptly out of the hot taps.  It must save me a little money on my water bill but not nearly enough to offset the extra cost of heating the hot water.

Qyburn

Reed_Richards said:

I have a system the circulates hot water from the cylinder round a loop and back to the cylinder.  All the hot taps run off this loop.  I run the recirculation pump for 5 minutes an hour (on a timer) whilst we are awake.  This is not a money saving option, but it does ensure that warm or hot water comes promptly out of the hot taps.  It must save me a little money on my water bill but not nearly enough to offset the extra cost of heating the hot water. 

That was normal in the systems I programmed for large buildings. In a school or similar you'd otherwise have to run off gallons and gallons before the water came hot. It was certainly considered a fuel and cost saving, although I don't think I ever saw it calculated. Sometimes it was purely passive by gravity circulation, with a valve shutting it off after hours.

FreeBear

victor2 said:

Zandoni said:

Don't use the hot tap to wash your hands, they are usually done before the heat gets through.

That's certainly the case for us in the kitchen - boiler is downstairs near the kitchen but pipe run goes upstairs to where the hot tank used to be then down to the kitchen. Takes forever to warm up!

Used to have a vented DHW cylinder in the back bedroom (heated by a back boiler in the room below). Hot water was always slow to arrive at  taps in the bathroom & kitchen, and lacked pressure/volume. Replumbed the system when I had a new combi boiler installed directly below the bathroom. Almost instant hot water delivery at mains pressure in the bathroom at the expense of a long wait in the kitchen thanks to some 12m of pipe.

bob2302

MP1995 said:

Unless the pipe ran outside the house the energy wasn't wasted. Although in summer it might be a waste, in winter it would add that heat back into the house.

It's not very efficient though. You take in very cold water from outdoors and then it drains at, at least, room temperature. In practice I end up discarding luke-warm water before I get hot water.

That said, I'm sceptical that a kettle is cheaper.

good_thyme

A quick update. We are getting better at not automatically using the hot tap for little jobs such as wetting a dishcloth or 'finger rinsing' (I think handwashing is a different task that needs hot water) and I've overcome my need to have scalding hot water for washing really greasy pans and dishes, so we now have it set to 45 degrees.
It is going to sound really d'oh! but because I wash up in Marigolds I hadn't appreciated how hot the water actually was and that it could be cooler and still cut through the grease. I took a meter reading and it's certainly down on a daily basis from what it was a few weeks ago so I'm hopeful that all of your advice has saved us some cash. Thank you all!

FreeBear

good_thyme said: We are getting better at not automatically using the hot tap for little jobs such as wetting a dishcloth or 'finger rinsing' (I think handwashing is a different task that needs hot water)

Soap is effective at removing germs, and running water flushes them away. Whilst hot water will kill bacteria, for near instant death, it needs to be 60°C or hotter - At that temperature, you will scald yourself. Recommended maximum water temperature at a tap (for hand washing) is just 44°C by the HSE in places such as care homes.

Scot_39

But that 44C is I guess generated very locally to taps using a thermostatic mixer valve.

But iirc the 60C remains the HSE requirement for any significant volumetric storage tanks / cylinders and distribution pipes.

There's also - for over a decade (c2010 ?) - a domestic equivalent limit - but that only applies to bath taps - to limit iirc to a slightly higher 48C.

As immersion in anything hotter a real risk of serious scalding / burns for young or elderly / frail - building regs were reportedly changed due to hundreds of cases of "severe scalding" being reported annually.

One of my ex employer fitted TMVs (class 2 or 3 ?) in every toilet - not sure if a wider requirement - or just an abundance of caution - to limit temps at multiple sink's (typically 3 sinks per location). 

FreeBear

Scot_39 said: But that 44C is I guess generated very locally to taps using a thermostatic mixer valve.

But iirc the 60C remains the HSE requirement for any significant volumetric storage tanks / cylinders and distribution pipes.

In a commercial environment (and quite a few rentals), a TMV is the standard way to reduce the temperature at the tap. HSR still recommends the hot water to be stored at 60°C subject to a suitable risk assessment. BUT this recommendation is only applicable to commercial (including care homes) and rented accommodation (the occupant is still at liberty to turn the thermostat down).

But to my mind, the risk of scalding is much greater than the very remote possibility of catching legionnaires disease.