Worcester boiler central heating temp

FreeBear

Ectophile said:

gazb_2 said:

We have the same boiler. What number would you recommend for a bungalow with 9” solid walls with radiators? Thanks 

As low as you can get away with. Modern boilers are more efficient at lower temperatures.

But if the house never gets up to temperature, then it's too low.

With a 40°C flow and 30°C return temperature, it is possible to get ~98% efficiency out of a modern boiler. But to operate at such a low flow/return temperature, the radiators need to be considerably larger than fitted in most homes. Level of insulation, draught proofing, and radiator size will dictate the optimum flow temperature.

Installed a new boiler earlier in the year along with larger radiators, and have settled on a 52°C flow temperature as a compromise between efficiency, gas consumption, and speed of heating. Have tried running the system at 40°C, and it is barely enough to maintain the temperature.

Need to install a heat meter & gas flow sensor so that I can monitor consumption and heat output.

gazb_2

How much larger do the radiators need to be? 150%, 200%? Thanks 

FreeBear

gazb_2 said: How much larger do the radiators need to be? 150%, 200%? Thanks 

Depends on what flow temperature the radiators had been sized at and the actual temperature you want to run at. This site provides a handy chart and calculator - https://www.clyderadiators.co.uk/delta-t-conversion

Do pay attention to how Delta-T (∆T) is calculated - It is not the same as the flow temperature.

matelodave

gazb_2 said:

How much larger do the radiators need to be? 150%, 200%? Thanks 

Very simply, if your radiators were designed with a flow temperature of 70 degrees to achieve a room temperature of 20 degrees your DeltaT = 70-20 = 50 degrees.

Reducing the flow temp to 50 degrees will give you a deltaT of  50-20 = 30degrees which means you'll reduce the heat output of the radiator by 50%. So to get the same amount of heat in the same amount of time you'd need to double their size.

However, although the peak heat output has been reduced you may find that heating for longer at a lower flow temperature could still keep you just as warm (although it will take longer to get the room up to temperature).

You should be aiming for the lowest flow temp you can get away with taking into account the time to reheat the room/house and the room temps you are comfortable with.

Think of it a bit like driving a car - blatt up the motorway at 70mph and keep slowing down and speeding up or cruise gently at 50. You'll still get there and, although it'll take a bit longer, your fuel consumption will be significantly less at the lower speed. and there's less stress on the car.

Alnat1

matelodave said:

Think of it a bit like driving a car - blatt up the motorway at 70mph and keep slowing down and speeding up or cruise gently at 50. You'll still get there and, although it'll take a bit longer, your fuel consumption will be significantly less at the lower speed. and there's less stress on the car.

I gave my dad a very similar comparison yesterday to help explain why there is a more economical way to run his boiler. He told me I know nothing, he's had boilers way longer than I have (since 1971 to my 1990) and insisted the boiler is meant to be run at 76C or it wouldn't have that option. 

He also heats a large old tank to 70C for 2 x 2 hours a day which he only uses for washing his hands and a daily shave, his shower is electric. I should say he did heat it to 70C, I've lowered it to 62C and my bro is going to decrease it down to 57C next week. The water was coming out of the taps scalding hot, dad is 87, I worry but he's a stubborn old ***

FreeBear

Alnat1 said:

matelodave said:

Think of it a bit like driving a car - blatt up the motorway at 70mph and keep slowing down and speeding up or cruise gently at 50. You'll still get there and, although it'll take a bit longer, your fuel consumption will be significantly less at the lower speed. and there's less stress on the car.

I gave my dad a very similar comparison yesterday to help explain why there is a more economical way to run his boiler. He told me I know nothing, he's had boilers way longer than I have (since 1971 to my 1990) and insisted the boiler is meant to be run at 76C or it wouldn't have that option.

If the whole heating system has been sized to run at 70°C or higher and the boiler is a vintage non-condensing model, it isn't going to improve efficiency by turning the flow temperature down. With a modern condensing boiler and "oversized" radiators (with TRVs), turn the flow temperature down a few degrees each time you visit. Dropping from 76°C down to 70°C will make difference to efficiency. Knock it back to 65°C a month later, and the efficiency should jump up noticeably (assuming a 20°C difference between flow & return). Would also be worth checking that the radiators have been balanced properly.

With a 20°C difference between flow & return, at a flow temperature of 70°C, the boiler will be running condensing mode and should be around 90% efficient. dropping to 65°C will gain a couple more percentage points, as will going down to 60°C. Going much lower, and you are only going to gain one or two % and the heating system may not heat the property effectively or quickly enough.

Alnat1

I believe the boiler is around 12-15 years old so not as old as the rest of the system and should be condensing type. I know it's a Glow Worm, a brand my dad may have asked for as we had that make in 2 houses when I was growing up, but I don't know the model. The radiators are definitely unbalanced, one bathroom doesn't heat at all, broken TRVs etc. He won't use the timer, turns it on and off manually and I think the room thermostat might not work. I live 2 hours drive away.

Unfortunately the boiler is in the kitchen and easily accessible to dad so he'd know if we altered the temperature and turn it back up. The tank can only be accessed by climbing on the bannister as it's in a high cupboard in the stairwell and allows us to be sneaky.

FreeBear

Alnat1 said:

I believe the boiler is around 12-15 years old so not as old as the rest of the system and should be condensing type. I know it's a Glow Worm, a brand my dad may have asked for as we had that make in 2 houses when I was growing up, but I don't know the model. The radiators are definitely unbalanced, one bathroom doesn't heat at all, broken TRVs etc. He won't use the timer, turns it on and off manually and I think the room thermostat might not work.

The CH system was probably designed with a 70°C flow temperature - Even that high, once the radiators are properly balanced, it should be operating in condensing mode. Efficiency is likely to be around 86% which isn't too bad.

The bathroom radiator probably needs bleeding (along with the others). So do that when balancing the system, and the gas bill should be reduced and the house heats up to a comfortable temperature.

JSHarris

At our old house I managed to find double finned rads that were the same physical width as the singles that the house was built with.  I went around swapping some of the singles for doubles (not the bedroom rads).  Meant I could turn the boiler flow way down and still get more then enough heat.  Not massively expensive, as all the rads came from B&Q, just took a bit of finagling to get the pipes to line up.  I think I recovered the cost of the rads the first winter, just from the saving in gas.  Only glitch was that the rads stuck out further and had a smaller gap at the back, which caused some marital disharmony over the way the curtains got caught on them.

gazb_2

How much of a saving would it be lowing the flow temp to say 40degrees from 60?