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

Astria

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

None whatsoever, but if the flow temperature is 75C then you need to have sufficiently sized radiators to drop approx 30C of heat before it returns to the boiler, so I would say the opposite is true - you are better off using a lower flow temperature to get a lower return temperature. In modern houses, a flow temperature of 55C may be ideal, but for older properties and properties with less insulation, then you may need 65C.

Cardew

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler. Otherwise any A+ rating is lost and your boiler will have the efficiency of a gas guzzling back boiler of old.

In practice this means turning the boiler temperature all the way up to max (72 degC or more) and balancing your radiators. To balance the radiators the TRV valves should temporarily be set to max and you adjust the lockshield valve (opposite end to TRV) so they all heat up at the same rate and the temperature differential across the radiator set to 12 degC. It helped me that I had a cheap temperature gun purchased from Lidl. The aim is to get the boiler return 20 degC lower, it needs to be no higher than 55 degC or there's no condensing.

I won't post any links, there's plenty of advice and guides via Google and they all say the same thing.

Welcome to the forum.

The very expensive Veissmann weather compensation fitted to my boiler does not agree with your theory!!

limecc

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

The lower the better, 50 degC would be great. Any higher than 55 degC and latent energy cannot be captured as exhaust vapour turns to liquid. In fact it's just expelled with the gas and the heat is lost. I haven't been around long enough to post links so Google search: How to balance and bleed your radiators on the Which dot co dot uk website.

which_co_uk/reviews/boilers/article/boiler-maintenance/how-to-balance-your-radiators-ae5wh1q2IyRH

Astria

limecc said:

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

The lower the better, 50 degC would be great. Any higher than 55 degC and latent energy cannot be captured as exhaust vapour turns to liquid. In fact it's just expelled with the gas and the heat is lost. I haven't been around long enough to post links so Google search: How to balance and bleed your radiators on the Which dot co dot uk website.

which_co_uk/reviews/boilers/article/boiler-maintenance/how-to-balance-your-radiators-ae5wh1q2IyRH

Yes, the lower the better return temperature, it doesn't matter about the flow temperature as long as you can get rid of the heat produced so the return temperature is 50c or less. So in effect, if you have larger or more radiators you can increase the output temperature, if you have less or smaller radiators you need to decrease the output temperature.

limecc

Astria said:

limecc said:

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

The lower the better, 50 degC would be great. Any higher than 55 degC and latent energy cannot be captured as exhaust vapour turns to liquid. In fact it's just expelled with the gas and the heat is lost. I haven't been around long enough to post links so Google search: How to balance and bleed your radiators on the Which dot co dot uk website.

which_co_uk/reviews/boilers/article/boiler-maintenance/how-to-balance-your-radiators-ae5wh1q2IyRH

Yes, the lower the better return temperature, it doesn't matter about the flow temperature as long as you can get rid of the heat produced so the return temperature is 50c or less. So in effect, if you have larger or more radiators you can increase the output temperature, if you have less or smaller radiators you need to decrease the output temperature.

You are correct and apologies for me missing or mis-reading yours and other replies. My Gas Safe installer said to have a high differential temp and set the boiler to max.

I was reading that radiators are sized according to flow temperature so a lower temp might not work like you say and in a traditional system like mine 65 degC minimum is needed to kill Legionalla in the stored water cylinder. Setting the pump speed to the lowest setting probably helps the radiators dissipate heat.

Cardew

limecc said:

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

The lower the better, 50 degC would be great. Any higher than 55 degC and latent energy cannot be captured as exhaust vapour turns to liquid. In fact it's just expelled with the gas and the heat is lost. I haven't been around long enough to post links so Google search: How to balance and bleed your radiators on the Which dot co dot uk website.

which_co_uk/reviews/boilers/article/boiler-maintenance/how-to-balance-your-radiators-ae5wh1q2IyRH

limecc said:

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

The lower the better, 50 degC would be great. Any higher than 55 degC and latent energy cannot be captured as exhaust vapour turns to liquid. In fact it's just expelled with the gas and the heat is lost. I haven't been around long enough to post links so Google search: How to balance and bleed your radiators on the Which dot co dot uk website.

which_co_uk/reviews/boilers/article/boiler-maintenance/how-to-balance-your-radiators-ae5wh1q2IyRH

 How to balance your radiators is different to how to run your heating. That is why modern heating systems have weather compensation and load compensation to keep the boiler running at optimum efficiency.

richardc1983

Watch the latest video, it is very interesting and easy to follow. It explains a lot... 

https://youtu.be/T022zY9I__0 

orrery

Or just get a controller that uses proportional control i.e. turns the system on and off in proportion to the need. If the need for heat is large than it just stays turned on until it gets within a degree or so of the desired target, then drops into proportional mode.

Turning on and off means that each 'on' period is short enough to prevent the return temperature rising too far.

BUFF

limecc said:

I was reading that radiators are sized according to flow temperature so a lower temp might not work like you say and in a traditional system like mine 65 degC minimum is needed to kill Legionalla in the stored water cylinder.

Generally your CH & DHW are separate & can be run at different temps. - you are not running DHW through your radiators.

skidnote

Is there any chance of a energy/money saving guide for those of us 'lucky' enough to have air source heat pumps?  They are not moneysaving unless configured properly, which I suspect most installers aren't smart enough to do (beyond turning them on and checking they work).  From what I understand, they are supposed to be running all the time, albeit at a lower constant temperature.