Advice on water temp feeds to tank and rads.

[Jon1234]

Hi Everyone,

I'm looking for a little advice so I can try and save a bit of money this winter (especially considering the new prices!)

I have an Ideal boiler (Vogue Max System 18) and a hot water tank (Heatrae Sadia Megaflo).

On the boiler I only have 1 dial to turn the water temp up or down (no separate dials for heating and water).

On the water tank, I can turn a dial (numbers 1-7) to set the water temp (so it cuts off water feed / stops boiler when temp is reached).

Currently, If I set the boiler to 60C, it will supply 60C water to my water tank (if the flow has been enabled) or 60C to my radiators (if the thermostat kicks in).

I use a google nest for the thermostat.

At the moment, the water temp is fine (I'd rather have it at 60C ish to kill off any bacteria), but the radiators in my home don't need to be anywhere near as hot (all rads do have TRV so I can turn it down to help).

As such, I'm looking for some advice on two fronts.

1) If a water tank receives water from the boiler at e.g. 30 Degrees C, does that mean the water in the tank can never be above 30C? Or does it mean that the water can get higher e.g. 60C (due to the tanks insulation) but will simply take longer to reach that desired temp. I suspect the tank temp increases would stop once it reached boiler temp setting but just wanted to check first (since this would solve problem 2 very quickly!)

2) Is there a way to allow two separate temperatures with this setup (either using what is there or by adding another part)? Or am I doomed to only have heating the same temp as my water tank? I can set the TRV valves but the rads do still get hot if the heating is on for long periods and Ideally I'd like to get the boiler condensing to save money.

Thanks in advance
Jon

 

[gmartine]

I don't think that boiler has two water temperature controls in built. The salmanella risk is well overstated in domestic environments so you'd be ok reducing flow temp to 50 deg and if you really want give the cylinder a higher temp blast every couple of weeks.

Adding a weather comp sensor and utilising open therm would be the next step, 3rd gen nest will do that.

 

[Chuck]

In the OP's circumstances, I'd set the boiler temp to 65°C. This is high enough to provide the DHW (cylinder thermostat set point at 60°C) without excessive boiler cycling. As long as the radiator system is reasonably balanced for a drop of at least 10° across each radiator the return temperature at the boiler will, in practice, be 50°C or below.

I don't share @gmartine's opinion that 'The [legionella] risk is well overstated in domestic environments'. Legionnaire's is a nasty disease (I know someone who got it and they were dangerously ill) and the domestic environment often involves showers, which are relatively high risk for transmission.

Here's what the HSE has to say on the subject:

HSE - Legionella and Legionnaires' disease

HSE looks at the symptoms of Legionnaires' disease and how it is treated

www.hse.gov.uk

 

[gmartine]

I should've added the proviso of your risk level...

 

[Chuck]

I should've added the proviso of your risk level...
[YouTube Source]

Firstly, in the first minute or so the "Heat Geek" claimed that storing DHW at 40°C would 'halve your hot water bill'. That's incorrect, it would halve the losses associated with the storage cylinder. For a Megaflo in an occupied house these are a small fraction of the cost of heating water. So, the benefit in terms of cost will be pretty small.

Secondly, since the recommendation to store domestic hot water at 60°C has been in force for many years it is no surprise that the overall domestic incidence rate is currently low. The question is "What would it be if everybody stored their water at 40°C?"

I didn't bother to watch further into the video so maybe Heat Geek corrects himself later but that's too late AFAIC.

I'm not disputing that it may be okay from a legionella-risk point of view to store water at lower than 60°C if the system includes effective disinfecting cycles and/or periodic testing. But, in a domestic context, these details are likely to be neglected.

Anyway, in my opinion professionals should be recommending best practice derived from authoritative sources, such as the HSE.

 

[ShaunCorbs]

Double thread

Advice on water feed to tank and rads (different temps)

Hi Everyone, (not sure if my last post worked so apologies if this is a duplicate). I have an Ideal Boiler (vogue max system 18) and a MegaFlo Water tank. On the boiler I only have 1 dial to turn the water temp up or down (no separate dials for heating and water). On the water tank, I can...

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