Central heating circulation pump - electric usage

[Dr Mike Oxgreen]

With the mild weather we currently have, I’ve set the flow temperature down low on the combi boiler to maximise gas saving from condensing. It’s currently running at about 45°C.

But I’m wondering: does this actually save money overall?

With the flow temperature this low, inevitably the heating warms the house more slowly, so the boiler’s circulation pump is running for longer. I’ve estimated in the past that this accounts for at least 150 Watts of electric while it’s running.

Given that electric is about three times as expensive as gas, do the numbers actually stack up? Does the cost saving in gas due to better condensing outweigh the extra electric cost of running the circulation pump longer?

Has anyone done some measurements and calculations on this?

[megaphone]

Good question, looking forward to someone working it out!

My combi runs at 60w total when CH is on. I run my CH flow temp at 45deg all winter.

[LocoBlade]

If it's a modern pump it won't use very much. We run our Vaillant boiler with weather compensation meaning the boiler runs pretty much 24/7 through winter. The heating system also has two Grundfos UPS3 pumps, one for each heating circuit in addition to the internal boiler pump that also run pretty much constantly and judging by last year's usage there's no discernible difference in our overall house electricity consumption between winter and summer months (May/June was low because we were on holiday for 2 weeks across that period)

Edited by LocoBlade on Thursday 24th October 22:06

[OutInTheShed]

LocoBlade]If it's a modern pump it won't use very much...... said:

It's not the age of the pump so much as how hard it's working.

If it's heavily loaded with a big pressure differential, because all the valves are nearly shut, it will use much more power than the same pump running at the same speed on a more open system.
Three houses ago, I had a GCH system which was small bore, and downstairs rads fed from the ceiling, the pump was working pretty hard there.

Current combi seems to modulate the pump in a complex inscrutable fashion, doesn't seem to use much electricity, but we do have the main rads fairly open.

[119]

OutInTheShed said:

LocoBlade]If it's a modern pump it won't use very much...... said:

It's not the age of the pump so much as how hard it's working.

If it's heavily loaded with a big pressure differential, because all the valves are nearly shut, it will use much more power than the same pump running at the same speed on a more open system.
Three houses ago, I had a GCH system which was small bore, and downstairs rads fed from the ceiling, the pump was working pretty hard there.

Current combi seems to modulate the pump in a complex inscrutable fashion, doesn't seem to use much electricity, but we do have the main rads fairly open.

The newer pumps adjust their speed on demand.

[B'stard Child]

My new DAB Evosta_3 displays the instantaneous W (as well as speed setting, pump head and m3/hr)

I am amazed at how little it consumes on speed setting 2 - between 12 and 16 Watts depending on how much resistance there is in the circuit

Old Grundfos on speed 2 was using 60 - 65 Watts (with similar set up) and 35 - 40 watts on speed setting 1

I don't think I'd be worrying too much about pump electrical consumption unless I had multiple pumps and was running them flat out

[LocoBlade]

119 said:

OutInTheShed said:

It's not the age of the pump so much as how hard it's working.

The newer pumps adjust their speed on demand.

Yes to both, newer pumps have more efficient motors and better modulation/control, but having multiple pumps perhaps circulating one zone each is generally more efficient than a single pump doing all the work

[B'stard Child]

B'stard Child said:

My new DAB Evosta_3 displays the instantaneous W (as well as speed setting, pump head and m3/hr)

I am amazed at how little it consumes on speed setting 2 - between 12 and 16 Watts depending on how much resistance there is in the circuit

Old Grundfos on speed 2 was using 60 - 65 Watts (with similar set up) and 35 - 40 watts on speed setting 1

I don't think I'd be worrying too much about pump electrical consumption unless I had multiple pumps and was running them flat out

In a strange quirk of fate the DAB pump expired tonight and I'm back to the old grunfoss stuck on speed 3 - it was popping 3 am fuses like Mrs BC pops chocolate

[.:ian:.]

The energy usage of a 100w pump will always be inconsequential compared to the energy usage of a boiler.

The wider question on whether it will be cheaper to run at low power all the time, well to supply xKWh it will always be cheaper running at 98% efficiency than 88%

The only difference is how long it will take to get up to the target temperature, if your house loses 8KWh and the boiler supplies 10KWh in low power mode, it will take an eternity to heat up from cold.