Boiler hot water setting for savings

avgjoe

Hello

Just came across a Daily mail article saying turn boiler temperature down for savings. 

My plumber told me to keep my combi on E setting to save which equivalates to about 65 degrees. 

The lowest setting I can change my boiler to is around 36 manually and I have had that for a while but not sure what is better for bills with low general water usage outside of dishwasher and washing machine and showers? 

Bendy_House

What type of boiler - combi or 'heat-only' (you have a hot tank?) And I presume it's less than, say, 10 years old?

If a combi, then turn the output control to as low as will still heat your rads the required amount to keep your house warm. Yes, that does mean you vary its output throughout the year, so that in milder weather it can be turned down lower, and then back up when really cold outside, and many modern boilers can have a 'weather compensator' fitted for just this purpose. Whether a homeowner would bother tweaking their boiler a half-dozen times a year for something-% savings is up to them.

If your boiler heats a hot cylinder, it's more tricky, since your stored hot water really should be at around 60oC in order to prevent the risk of Legionnaire's disease. That in turn means that the boiler needs to be supplying the system water at above this temp, or else it simply won't be able to raise the cylinder temp quickly enough. Ie, if the boiler was outputting at 60oC itself, then it would likely never get the DHW to 60oC, and the boiler would be running constantly!

The answer is - I've just realised I haven't a clue.

What IS the answer? Do you NEED to have a heat-only boiler set to ~70oC for it to simply do its job? Are there any models with separate DHW and CH output settings?

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

rudigarude

I've actually wondered the same thing. My boiler has two temperature settings, one for radiators and one for hot water. It's a combi boiler. The radiator control sets an actual temperature, set to 50C (not that it's used right now) and then the hot water control has values from 1-6 and e. So I've set that to e.

However, the water is hot, hotter than it needs to be from the tap. I've considered messing with that setting but I just assumed that the "eco" mode would be best. I have no idea if that's the case. It's a good question though and I'd also be interested in hearing what others think on the forum.

Bendy_House

Thanks Rudi.

Yes, combis will have two separate settings like this.

Read your instructions to see if 'eco' also means that the 'pre-heat' setting is or is not engaged. It's hard to know which is best! For instance, if pre-heat is 'on', then you'll get hot water out your tap much faster than if the boiler is cold. So, you use more gas, but save water. And vicky-verka.

In general, tho', surely the lower the hot water delivery temp setting, the less gas that'll be used?

Section62

Bendy_House said:

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

Not strictly the case - the water on the stored side may still become contaminated and could potentially pose quite a serious risk to people living in the property and/or neighbours/passers-by.

Also, the water in the HW distribution system can still become contaminated - the isolation of the two parts of the system in terms of water containment doesn't stop the water in the HW distribution system sitting around at temperatures where legionella thrive.

The issues are temperature and time.

avgjoe

It's a boiler with radiator and hot water via same dial but can switch radiators off, which I have done. 

The boiler is also connected to a tank. 

Mainly worried about energy savings more than anything else. Any suggestions? 

Bendy_House

Section62 said:

Bendy_House said:

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

Not strictly the case - the water on the stored side may still become contaminated and could potentially pose quite a serious risk to people living in the property and/or neighbours/passers-by.

Also, the water in the HW distribution system can still become contaminated - the isolation of the two parts of the system in terms of water containment doesn't stop the water in the HW distribution system sitting around at temperatures where legionella thrive.

The issues are temperature and time.

Remind me to add these pedantic caveats to every post I make from now on.

Sheeesh.

Bendy_House

avgjoe said:

It's a boiler with radiator and hot water via same dial but can switch radiators off, which I have done. 

The boiler is also connected to a tank. 

Mainly worried about energy savings more than anything else. Any suggestions? 

Nope!

Until someone who does know can tell us how you can output that boiler automatically at 50oC for CH and 75oC for DHW.

Section62

Bendy_House said:

Section62 said:

Bendy_House said:

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

Not strictly the case - the water on the stored side may still become contaminated and could potentially pose quite a serious risk to people living in the property and/or neighbours/passers-by.

Also, the water in the HW distribution system can still become contaminated - the isolation of the two parts of the system in terms of water containment doesn't stop the water in the HW distribution system sitting around at temperatures where legionella thrive.

The issues are temperature and time.

Remind me to add these pedantic caveats to every post I make from now on.

Sheeesh.

You call it "pedantic". I call it giving people the correct advice about a health and safety issue.

Bendy_House

Section62 said:

Bendy_House said:

Section62 said:

Bendy_House said:

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

Not strictly the case - the water on the stored side may still become contaminated and could potentially pose quite a serious risk to people living in the property and/or neighbours/passers-by.

Also, the water in the HW distribution system can still become contaminated - the isolation of the two parts of the system in terms of water containment doesn't stop the water in the HW distribution system sitting around at temperatures where legionella thrive.

The issues are temperature and time.

Remind me to add these pedantic caveats to every post I make from now on.

Sheeesh.

You call it "pedantic". I call it giving people the correct advice about a health and safety issue.

OP, and anyone else reading this thread, I am soooo sorry, but I should point out that a Heat Store can cause health issues under certain conditions.

These could include not having the system water treated against nasty things, and then that system water gets out and does stuff to you. I will make certain that I always add this warning in all my future posts about anything 'system' related.

Also, there are circumstances where the system water and the DHW water could cross-contaminate. I have seen it happen once. So it's a valid concern. It could, of course, happen to any stored water system, not just a heat store. Come to think of it, it could even happen in a combi boiler, within the PtoP exchanger.

Basically, folk, if you run a 'system', you are at risk. Unless you follow the manufacturer's instructions. And that's no guarantee. So, think about whether you really want to run a system.

If you don't run a system, you are at an even greater risk.

Basically, we're all ....

Section62

Bendy_House said:

Section62 said:

Bendy_House said:

Section62 said:

Bendy_House said:

And is that another reason why Heat-Stores will take over from 'hot cylinders'? The former can be kept at ~45oC without risk, since the stored water is isolated from the DHW supply.

Not strictly the case - the water on the stored side may still become contaminated and could potentially pose quite a serious risk to people living in the property and/or neighbours/passers-by.

Also, the water in the HW distribution system can still become contaminated - the isolation of the two parts of the system in terms of water containment doesn't stop the water in the HW distribution system sitting around at temperatures where legionella thrive.

The issues are temperature and time.

Remind me to add these pedantic caveats to every post I make from now on.

Sheeesh.

You call it "pedantic". I call it giving people the correct advice about a health and safety issue.

OP, and anyone else reading this thread, I am soooo sorry, but I should point out that a Heat Store can cause health issues under certain conditions.

These could include not having the system water treated against nasty things, and then that system water gets out and does stuff to you. I will make certain that I always add this warning in all my future posts about anything 'system' related.

Also, there are circumstances where the system water and the DHW water could cross-contaminate. I have seen it happen once. So it's a valid concern. It could, of course, happen to any stored water system, not just a heat store. Come to think of it, it could even happen in a combi boiler, within the PtoP exchanger.

Basically, folk, if you run a 'system', you are at risk. Unless you follow the manufacturer's instructions. And that's no guarantee. So, think about whether you really want to run a system.

If you don't run a system, you are at an even greater risk.

Basically, we're all ....

There's a difference between not mentioning a potential risk because the risk is incredibly remote (e.g. a perforation of a combi boiler heat exchanger) - and in actively stating that something is "without risk" when that isn't true.

The difference is subtle, and I guess is quite easily missed.

However, the bigger point still being missed is the isolation of one lot of water from another is not an absolute protection against legionella.  There are situations where dangerous levels of legionella could grow in either side, the issue here isn't necessarily about 'leakage' from one side to the other.

The reference to "isolated" in your post was a red herring.