Energy myth-busting: Is it cheaper to have heating on all day?

richardc1983

If this is a normal domestic combi installation, in a relatively modern copper piped system, then there is no need to worry about legionella. The hot water in use comes direct from the chlorinated rising main and is heated without venting, so retains its chlorine. There is no storage and no circulation. My only precaution - if any - would be to clean and bleach the shower heads once a year. Water in a combi boiler and closed loop radiator system is moving it is not sitting about either. 

https://www.plumbersforums.net/threads/question-about-dhw-temp-and-legionnaires.119907/

BUFF

richardc1983 said:

At 70c flow temp your boiler will never be in condensing mode. Condensing starts at 55c and then below, so the cooler the water going back to the boiler the better. Try it at 55-60c and see if there’s any improvement. Ratings are at a 45c return so if you can manage at 50c flow temp and you can get 45c return back to the boiler from the rads then you are winning. 

Yes it might take a little longer to warm up but your boiler will be working more efficiently and recovering more heat from the gases that would otherwise just go out the flu. 

Assuming that a) it is a condensing boiler & b) the system is running radiators with the typical 20C difference between boiler flow & return that is not true as 70C flow would give 50C return. It's the return temp that needs to be under 55C to condense not the flow.
However, I agree that the lower that you can get it the better & I run my flow temp ~53-55C (giving return in the low 30sC).

As for Ultrasonics question about combis - combis tend to be less efficient at dhw than ch & for dhw than regular or system boilers.

BUFF

Ultrasonic said:

What I've just been looking for but failed to find is some representative data on how the efficiency may vary with temperature.  Also, isn't Legionella a concern if water is below 60°C?

I suspect the relatively small size radiators in my house may become an issue if I drop the temperature too low but I'll only know by trying I suppose.

Your ch  loop is a sealed system & should have chemical treatments in it. If you want to every week/month or whatever you could run it at over 60C for a while.

richardc1983

BUFF said:

richardc1983 said:

At 70c flow temp your boiler will never be in condensing mode. Condensing starts at 55c and then below, so the cooler the water going back to the boiler the better. Try it at 55-60c and see if there’s any improvement. Ratings are at a 45c return so if you can manage at 50c flow temp and you can get 45c return back to the boiler from the rads then you are winning. 

Yes it might take a little longer to warm up but your boiler will be working more efficiently and recovering more heat from the gases that would otherwise just go out the flu. 

Assuming that a) it is a condensing boiler & b) the system is running radiators with the typical 20C difference between boiler flow & return that is not true as 70C flow would give 50C return. It's the return temp that needs to be under 55C to condense not the flow.
However, I agree that the lower that you can get it the better & I run my flow temp ~53-55C (giving return in the low 30sC).

As for Ultrasonics question about combis - combis tend to be less efficient at dhw than ch & for dhw than regular or system boilers.

Yep naturally assuming it;s a condensing boiler.

Very difficult to get a 20c difference nowadays. I balanced my system and struggled to get a 10c diff. Maybe from a cold start yes but when running it;s more like a 10c sometimes less and if you have microbore pipework etc even worse. 

richardc1983

BUFF said:

Ultrasonic said:

What I've just been looking for but failed to find is some representative data on how the efficiency may vary with temperature.  Also, isn't Legionella a concern if water is below 60°C?

I suspect the relatively small size radiators in my house may become an issue if I drop the temperature too low but I'll only know by trying I suppose.

Your ch  loop is a sealed system & should have chemical treatments in it. If you want to every week/month or whatever you could run it at over 60C.

When I have it serviced my engineer does his checks and he always ramps it up for half an hour to get his readings. 

BUFF

richardc1983 said:

BUFF said:

richardc1983 said:

At 70c flow temp your boiler will never be in condensing mode. Condensing starts at 55c and then below, so the cooler the water going back to the boiler the better. Try it at 55-60c and see if there’s any improvement. Ratings are at a 45c return so if you can manage at 50c flow temp and you can get 45c return back to the boiler from the rads then you are winning. 

Yes it might take a little longer to warm up but your boiler will be working more efficiently and recovering more heat from the gases that would otherwise just go out the flu. 

Assuming that a) it is a condensing boiler & b) the system is running radiators with the typical 20C difference between boiler flow & return that is not true as 70C flow would give 50C return. It's the return temp that needs to be under 55C to condense not the flow.
However, I agree that the lower that you can get it the better & I run my flow temp ~53-55C (giving return in the low 30sC).

As for Ultrasonics question about combis - combis tend to be less efficient at dhw than ch & for dhw than regular or system boilers.

Yep naturally assuming it;s a condensing boiler.

Very difficult to get 70/30 nowadays. I balanced my system and struggled to get a 10c diff. Maybe from a cold start yes but when running it;s more like a 10c sometimes less and if you have microbore pipework etc even worse. 

I take it that is a typo & should have been 70/50? Did people ever run 70/30C? It used to be 80/60 pre-condensing.
Didn't you say somewhere that your flow temp is 35C? If so, I can understand why you struggle to get a differential of 20C especially if you are perhaps running a room temp in the 20Cs (I heat to 16C).

richardc1983

BUFF said:

richardc1983 said:

BUFF said:

richardc1983 said:

At 70c flow temp your boiler will never be in condensing mode. Condensing starts at 55c and then below, so the cooler the water going back to the boiler the better. Try it at 55-60c and see if there’s any improvement. Ratings are at a 45c return so if you can manage at 50c flow temp and you can get 45c return back to the boiler from the rads then you are winning. 

Yes it might take a little longer to warm up but your boiler will be working more efficiently and recovering more heat from the gases that would otherwise just go out the flu. 

Assuming that a) it is a condensing boiler & b) the system is running radiators with the typical 20C difference between boiler flow & return that is not true as 70C flow would give 50C return. It's the return temp that needs to be under 55C to condense not the flow.
However, I agree that the lower that you can get it the better & I run my flow temp ~53-55C (giving return in the low 30sC).

As for Ultrasonics question about combis - combis tend to be less efficient at dhw than ch & for dhw than regular or system boilers.

Yep naturally assuming it;s a condensing boiler.

Very difficult to get 70/30 nowadays. I balanced my system and struggled to get a 10c diff. Maybe from a cold start yes but when running it;s more like a 10c sometimes less and if you have microbore pipework etc even worse. 

I take it that is a typo & should have been 70/50? Did people ever run 70/30C? It used to be 80/60 pre-condensing.
Didn't you say somewhere that your flow temp is 35C? If so, I can understand why you struggle to get a differential of 20C especially if you are perhaps running a room temp in the 20Cs (I heat to 16C).

Yes sorry, it’s late I have been up nearly 20 hours lol.

I meant 70/50 many systems now are 50/30 though which is what I meant though. 

My flow temp can be 35c or down to 30c which is the min flow temp my boiler can be set at. The room temp is 19c and sometimes put to 20c on an evening if I haven;’t moved much. So to get a 20c return temp the return back to the boiler would need to be 10c which is lower than the actual room temp so you don’t get that, it generally is 8-10c but if it’s not particularly cold or there is low load that can be about 5c difference in supply and return. THe lower your flow temp the closer you are get to ambient room temp so the difference is less. 

Of course if you had those water filled fan forced fan convectors then you would likely remove more heat from the system some of these I have seen designed with flows as low as 25c and it works great with UFH. 

Ultrasonic

richardc1983 said:

If this is a normal domestic combi installation, in a relatively modern copper piped system, then there is no need to worry about legionella. The hot water in use comes direct from the chlorinated rising main and is heated without venting, so retains its chlorine. There is no storage and no circulation. My only precaution - if any - would be to clean and bleach the shower heads once a year. Water in a combi boiler and closed loop radiator system is moving it is not sitting about either. 

https://www.plumbersforums.net/threads/question-about-dhw-temp-and-legionnaires.119907/

I was talking exclusively about the heating system. I have zero concerns regarding the hot water.

It would be helpful if you quoted specific points you're responding to by the way, rather than simply posting and leaving others to figure out the context.

Ultrasonic

BUFF said:
If you want to every week/month or whatever you could run it at over 60C for a while.

That thought occurred to me actually, and would alleviate any possible concerns. 

I dug out the installation paperwork for my boiler and in pen it's been filled out to say that the 'Central heating flow temperature' was 70°C and that the 'Central heating return temperature' was 60°C. I've no idea if this was measured to estimated but it does suggest that a 10°C temperature drop may be a more realistic estimate than 20°C. Possibly this may depend on the starting temperature though, in that if the house is cold I'd guess more heat will be lost initially?

Also on the paperwork was mention of an 'inhibitor' named Fernox F1 but from a quick Google this appears to be more for inhibiting corrosion than preventing bacteria growth.

As I'll be home all of today I'm giving a 60°C setting a try (rather than 70°C). It definitely took longer to heat up this morning (as would be expected). It used less energy before the 18°C room temperature was reached to switch the heating off but I think the air temperature didn't 'overshoot' as much as normal so that the room hadn't got as warm.

QrizB

Ultrasonic said:

BUFF said:
If you want to every week/month or whatever you could run it at over 60C for a while.

That thought occurred to me actually, and would alleviate any possible concerns.

That's what I do with mine. My flow temp is usually 50-55C but once a month I turn it up to max and heat a tankful of water.