Boiler water temp

Mikemoreton36

Octopus suggest a combi boiler radiator water temp of 50°. Most of the advice from boiler companies suggest a temp of 70°. The lower the temp, the longer it will take to heat a space so, other than improving the efficiency of the boiler, the saving on gas is marginal. Lower temps means the room temp will take longer to reach the set temp and your boiler will be on longer thus consuming more gas. Remember the old adage"there's no such thing as a free lunch". 

Verdigris

The idea of running at a lower temperature is to ensure the return flow is at a low enough temperature to fully exploit the condensing effect of the boiler, thus leading the better utilisation of gas. Modern boilers have modulating burners, so even though the boiler may be on for longer, the flame is smaller.

matelodave

Mikemoreton36 said:

Octopus suggest a combi boiler radiator water temp of 50°. Most of the advice from boiler companies suggest a temp of 70°. The lower the temp, the longer it will take to heat a space so, other than improving the efficiency of the boiler, the saving on gas is marginal. Lower temps means the room temp will take longer to reach the set temp and your boiler will be on longer thus consuming more gas. Remember the old adage"there's no such thing as a free lunch". 

Compare running your boiler at a lower temperature (when it will be in condensing mode and therefore more efficient rather than at 70 degrees)) with thrashing up the M1 at 70mph or cruising at 50mph.

 You'll still get there, but at 50 it will take a bit longer but will cost you a lot less. 

At 70 your boiler will be firing up and shutting down rather than just idling at 50. The same with driving, blatting up to 70 and then slowing down and speeding up is a lot less efficient than cruising along at say 50. (my car does around 48mpg at 70mph and around 58-60mpg at 50mph which although a bit boring is a worthwhile saving)

[Deleted User]

The science indicates the lower the boiler RETURN temperature the better for efficiency. Most research indicates that very few boilers installed in the UK are running in a condensing mode. A large plume of steam is not an indication that the boiler is condensing.

BUFF

Mikemoreton36 said:

Octopus suggest a combi boiler radiator water temp of 50°. 

I would suggest that for a large % of the UK this is probably not the best advice as their radiators/system were not sized to run at this temperature.
However, for condensing boilers a return temp of 55C> (thereby ensuring condensing occurs) would typically mean a flow temp. of ~70-75C>. If you can run lower return temp than 55C the more efficient the boiler will be but it's single figure % gains.
Ultimately it's an individual's call on a balance between cost, comfort & convenience.

Running lower temps also tends to make life easier for the boiler & therefore improve reliability/life.

I do wonder though what impact on cost savings (given that electricity is much deare than gas per kWh)  running the pump & fan for much longer causes?

QrizB

BUFF said:

Mikemoreton36 said:

Octopus suggest a combi boiler radiator water temp of 50°. 

I would suggest that for a large % of the UK this is probably not the best advice as their radiators/system were not sized to run at this temperature.

I would counter by suggesting it will work fine so long as we don't have another Beast for the East. Heat loss calcs assume a sub-zero outdoor temp (varies by region) but most of the time it's warmer than that, so the reduced rad output is still sufficient to maintain the design temperature.

If we do have a cold spell, it's only a moment's work to turn the flow temperature up.

You can think of it as DIY weather compensation!

Verdigris

You can think of it as DIY weather compensation!

We all have to get our entertainment where we can.

BUFF

QrizB said:

BUFF said:

Mikemoreton36 said:

Octopus suggest a combi boiler radiator water temp of 50°. 

I would suggest that for a large % of the UK this is probably not the best advice as their radiators/system were not sized to run at this temperature.

I would counter by suggesting it will work fine so long as we don't have another Beast for the East. Heat loss calcs assume a sub-zero outdoor temp (varies by region) but most of the time it's warmer than that, so the reduced rad output is still sufficient to maintain the design temperature.

If we do have a cold spell, it's only a moment's work to turn the flow temperature up.

You can think of it as DIY weather compensation!

I am aware of this & already practice it.
However, I live in a pre-1919 building (which makeup ~20% of the UK's housing stock) with a condensing boiler & what would be considered oversize radiators on a traditional boiler system (but probably still too small for a heat pump). Even running at a flow temp of 53C during this mild winter I would say is pushing the boundaries of what I think most people would consider a reasonable comfort/convenience balance (you can also chuck in cost if you want ). & I am someone who is happy at 16C when many are not ...

Verdigris

Even running at a flow temp of 53C during this mild winter

It's the return temperature that matters.

Ultrasonic

BUFF said:

Mikemoreton36 said:

Octopus suggest a combi boiler radiator water temp of 50°. 

I would suggest that for a large % of the UK this is probably not the best advice as their radiators/system were not sized to run at this temperature.
However, for condensing boilers a return temp of 55C> (thereby ensuring condensing occurs) would typically mean a flow temp. of ~70-75C>. If you can run lower return temp than 55C the more efficient the boiler will be but it's single figure % gains.
Ultimately it's an individual's call on a balance between cost, comfort & convenience.

Running lower temps also tends to make life easier for the boiler & therefore improve reliability/life.

I do wonder though what impact on cost savings (given that electricity is much deare than gas per kWh)  running the pump & fan for much longer causes?

The installation paperwork for my boiler suggests the return temperature is 10°C below the flow temperature, so running my system at a 70°C flow temperature is unlikely to lead to any condensation.

@Mikemoreton36 provided you have a condensing boiler I'd suggest you just give it a try. I dropped my boiler flow temperature from 70°C to 55°C about a week ago and it's working fine. It's a little slower to heat up obviously, but that's it. As per the graph posted above it's probably about 5% more efficient this way. Not enough to reliably be able to detect but it seems the smarter thing to do. Should the weather get really cold outside so that I can't heat my home OK this way, I'll just turn the flow temperature up again for that period.

BUFF

Verdigris said:

Even running at a flow temp of 53C during this mild winter

It's the return temperature that matters.

yes, but  it's extremely unlikely that the return temp is higher than the flow   so the return temp is even lower (usually 10C-20C lower depending upon system & setup)... 

in the Octopus advice  they advise a flow temp of 50C which, based on my own personal experience at a slightly higher temp, is imo probably a step too far for many. I  think that a significant no. (mostly those living in older buildings) would not find it a comfortable/convenient way to run at that low a temp..