Maximum safe temperature

[pmx_super]

Hi,

the hotter I get my hot water the better the shower I can have. Is there a limit to how hot I should set the thermostat on my immersion heaters? They go up to 80 - is this sensible? What is the downside (besides cost of heating and risk of scalding)?

Thanks,
James.

 

[chrishutt]

Don't set your domestic hot water higher than 60C. Above this temperature you will get scale forming and blocking pips, etc. and it is potentially dangerous.

showering temperatures are around 40C so there can't be any advantage in DHW much hotter than this except that the store of it will last longer. Perhaps you need a thermostatic shower?

 

[pmx_super]

I have a venturi shower fed by mains cold (drawing hot from the tank). I have a non-existant head of water, so according to the operating instructions the hotter the hot is the better performance I can expect. This bears out in practice. At 60 i need the shower head at chest level for a 'hot' shower. At 70 I can have it just above my head. I didn't want to set the thermostat higher than this since a 20 degree jump seemed not very sensible (80 is the max).

So are you saying that the rate at which limescale gathers increase exponentially with temperature of water? Will this just kill the elements quicker (which will go in time anyway) or could it be more damaging elsewhere? And where is the danger? Only of scalding at the hot tap or something else?

 

[ChrisR]

are you saying that the rate at which limescale gathers increase exponentially with temperature

No he's saying what he said, which is right. Above 60 expect your cylinder and pipes to get to look like the inside of your kettle until it all blocks up.
Water at 80 will give full thickness burns in about 1 second.

There are pumps about (Triton, grundfos) which will boost water pressure a little (a few metres head), for under £100. On the hot that should work. A small inline heater could also work but they usually expect an open vent so probably not usable, scour the net...

 

[chrishutt]

I have a venturi shower

It would help if you'd said that in the first place. The simplest solution to the problem might be to raise the height of the cistern feeding the hot water cylinder. Even a few inches will help. Otherwise, as ChrisR suggests, you could try a pump on the hot supply pipe - but best check with venturi shower manufacturer (which one?) first in case it causes some problem.

 

[pmx_super]

are you saying that the rate at which limescale gathers increase exponentially with temperature

No he's saying what he said, which is right. Above 60 expect your cylinder and pipes to get to look like the inside of your kettle until it all blocks up.
Water at 80 will give full thickness burns in about 1 second.

There are pumps about (Triton, grundfos) which will boost water pressure a little (a few metres head), for under £100. On the hot that should work. A small inline heater could also work but they usually expect an open vent so probably not usable, scour the net...

I gather limescale accumulates regardless of the temperature of the water - so clearly you are saying that hotter water accumulates limescale faster. I was wondering how much faster. If it reduces the lifetime of my element from 7 to 4 years say I could accept that. If it means the pipework will need replacing after 2 years instead of 20 i can't.

I can't pump the hot water since the feeder tank is too small for regs. There is no room for a bigger one without getting a new smaller hot water tank (££). Nor is there room to raise the feeder tank.

Quite frankly the whole setup is a mess and needs ripping out. It was done by new about 4 years ago by some spanner who owned the flat before me. I just can't afford to put it all right and raising the stat temp seemed the cheapest and easiest solution. If you're saying it'll cost me a fortune down the line though, I'll turn it back down.

Thanks for all the input.

James.

 

[pmx_super]

I have a venturi shower

It would help if you'd said that in the first place. The simplest solution to the problem might be to raise the height of the cistern feeding the hot water cylinder. Even a few inches will help. Otherwise, as ChrisR suggests, you could try a pump on the hot supply pipe - but best check with venturi shower manufacturer (which one?) first in case it causes some problem.

Sorry, I should have. I was being lazy.

I have a Trevi Boost.

 

[chrishutt]

I have a Trevi Boost.

Trevi appear to have dropped it from their web site, so they may have stopped making them (leaving only the New Team Jetstream on the Venturi market!). Perhaps you're not the only one to be disappointed with the performance.

I've heard of widespread disappointment from other sources too. It may be due to installations that don't comply with the design parameters, so not necessarily the fault of Trevi, just poor calibre of British plumbers (present company excepted).

I can see the temptation to raise the DHW temp, but that may well do rapid damage to the shower valve! The whole situation will improve soon with the warmer weather, so plan to upgrade before next winter.

 

[pmx_super]

I have a Trevi Boost.

Trevi appear to have dropped it from their web site, so they may have stopped making them (leaving only the New Team Jetstream on the Venturi market!). Perhaps you're not the only one to be disappointed with the performance.

I've heard of widespread disappointment from other sources too. It may be due to installations that don't comply with the design parameters, so not necessarily the fault of Trevi, just poor calibre of British plumbers (present company excepted).

I can see the temptation to raise the DHW temp, but that may well do rapid damage to the shower valve! The whole situation will improve soon with the warmer weather, so plan to upgrade before next winter.

I think it's probably due to the latter. The guy who put my system in could not have possibly been a professional plumber. I've had two plumbers in to look and both have pretty much just walked away when they saw the access that has been left to the tank & cylinder.

I actually found some graphs where ideal standard explain the recommended operating conditions and it all seems to match up with what I've found. They say that for 0m head of water and 1.5bar cold pressure, you need hot feed of 70C to get a 42C outlet temperature. I'd have to raise the tank another 0.5m to bring that down to 65C apparently.