Cost of running hot water secondary return
Discussion
I'd be interested to hear from others on this topic.
Recently installed unvented system with hot water return and pump.
The tank is set to 65 and you get 63 deg water at the taps in a matter of seconds (possibly too hot, but that's another question).
If I turn off the boiler, then about an hour later, the water temp at the tap has already dropped to about 53.
This suggests that the secondary return loop has 'cost' 10 deg of temperature from the 300L tank in only an hour.
An online calculator suggests this is ~3.5kwh of energy loss.
Over a year, this means it might cost be £1k+ to run (16 hours a day x 3.5kwh x 7p).
Is this simply the price people pay for convenience? Or does this mean my pipes are not insulated properly?
(note: house is 5 bed 230 sqm. As a control experiment, HW loses very little temperature in the tank with the pump off)
Recently installed unvented system with hot water return and pump.
The tank is set to 65 and you get 63 deg water at the taps in a matter of seconds (possibly too hot, but that's another question).
If I turn off the boiler, then about an hour later, the water temp at the tap has already dropped to about 53.
This suggests that the secondary return loop has 'cost' 10 deg of temperature from the 300L tank in only an hour.
An online calculator suggests this is ~3.5kwh of energy loss.
Over a year, this means it might cost be £1k+ to run (16 hours a day x 3.5kwh x 7p).
Is this simply the price people pay for convenience? Or does this mean my pipes are not insulated properly?
(note: house is 5 bed 230 sqm. As a control experiment, HW loses very little temperature in the tank with the pump off)
We have a long, thin house with the unvented tank at one end and the main bathroom at he other, so the installer recommended a recirculation pump. However it doesn't have to run continuously. Ours is on a time-switch and just runs for an hour in the morning when it's most useful.
I had wondered about getting it to operate remotely, triggered by a button or even the bathroom light switch.
I had wondered about getting it to operate remotely, triggered by a button or even the bathroom light switch.
I've noticed similar with our newly installed heating system with hot water recirc although I don't get as much drop. I heat my tank to 55c in the morning, that does 2 showers and stays hot enough until mid afternoon when it's dropped to about 40c at the mid tank sensor and I trigger it to heat back up which then does the evening.
If not already try and insulate all the hot pipes wherever you can under floorboards etc and ensure the pump is only running when you need it. We've got a Grundfos pump with a remote temperature probe that clamps on the top tank outlet and learns when the hot water is turned on then builds up a schedule based on that so only runs at times hot water is likely to be used. That works reasonably well but I still think a smart system could take it a stage further, some cheap smart home motion sensors and a smart switch on the pump, then a routine to only run the pump for a couple of minutes to prime the system when movement is detected in the vicinity of an outlet (when someone enters the bathroom for example).
If not already try and insulate all the hot pipes wherever you can under floorboards etc and ensure the pump is only running when you need it. We've got a Grundfos pump with a remote temperature probe that clamps on the top tank outlet and learns when the hot water is turned on then builds up a schedule based on that so only runs at times hot water is likely to be used. That works reasonably well but I still think a smart system could take it a stage further, some cheap smart home motion sensors and a smart switch on the pump, then a routine to only run the pump for a couple of minutes to prime the system when movement is detected in the vicinity of an outlet (when someone enters the bathroom for example).
Edited by LocoBlade on Saturday 12th March 10:33
LocoBlade said:
I've noticed similar with our newly installed heating system with hot water recirc although I don't get as much drop. I heat my tank to 55c in the morning, that does 2 showers and stays hot enough until mid afternoon when it's dried to about 40c at the mid tank sensor and I trigger it to heat back up which then does the evening.
.
I might try running at 55 degrees also. With having instant HW, 65 is just too hot. Seems silly to pump it around that hot only to mix it again with cold..
Whereas without the pump, hotter probably better so it reacts more quickly.
I know some are concerned about bacteria. But perhaps I can just turn it up once a week or so to make sure. Maybe also 55 at the stat means 60+ at the top of the tank.
I did a bit of Googling as I didn't know what this set up was and this link suggests....
[i]To avoid high energy bills it is important that the setting on the thermostat in the flow boiler is
reduced in temperature. This should be reset to approximately 45oC [/i]
https://www.kensaheatpumps.com/wp-content/uploads/...
[i]To avoid high energy bills it is important that the setting on the thermostat in the flow boiler is
reduced in temperature. This should be reset to approximately 45oC [/i]
https://www.kensaheatpumps.com/wp-content/uploads/...
TimmyMallett said:
I did a bit of Googling as I didn't know what this set up was and this link suggests....
[i]To avoid high energy bills it is important that the setting on the thermostat in the flow boiler is
reduced in temperature. This should be reset to approximately 45oC [/i]
https://www.kensaheatpumps.com/wp-content/uploads/...
That's an interesting set up because the loop can run at a temp lower than the tank itself. However that wouldn't work with my setup unfortunately. The return goes straight back into the cylinder.[i]To avoid high energy bills it is important that the setting on the thermostat in the flow boiler is
reduced in temperature. This should be reset to approximately 45oC [/i]
https://www.kensaheatpumps.com/wp-content/uploads/...
We also have a long bungalow with a centrally located HW cylinder with a hot water loop. It is pumped via a Grundfos Auto Adapt Comfort 15-14 BAPM which is a pump designed specifically for this purpose.
Replacement cost, looking online, varies from a whopping £163 to a humungous £290!
It is meant to be a clever piece of kit that can adapt to your lifestyle - how it works I have no idea and how it can predict my lifestyle? Even I dunno who I am some days!
How much it costs to run a loop with this pump is a complete mystery that I would love to know the answer to.
I have no idea how well the previous owner insulated the pipes but I'll bet the mice have chewed most of it off.
Replacement cost, looking online, varies from a whopping £163 to a humungous £290!
It is meant to be a clever piece of kit that can adapt to your lifestyle - how it works I have no idea and how it can predict my lifestyle? Even I dunno who I am some days!
How much it costs to run a loop with this pump is a complete mystery that I would love to know the answer to.
I have no idea how well the previous owner insulated the pipes but I'll bet the mice have chewed most of it off.
LocoBlade said:
We've got a Grundfos pump with a remote temperature probe that clamps on the top tank outlet and learns when the hot water is turned on then builds up a schedule based on that so only runs at times hot water is likely to be used.
We've got similar, but I turned it off shortly after having it installed (about 2 months) as I couldn't understand how it worked and sensed. I bought a Grundfos UP 15-14BA PM(80) Brass Comfort Hot Water Circulator Pump with Auto Adapt which does what you say - senses the temp rise when the 'call for hot water' is demanded, then learns from that - but if it learns that I need hot water at 7:00am but am then away for a few weeks, then at 7:00am the pump starts circulating and the temp sensor senses the heat flow which re-enforces the schedule - so how does it ever learn a new schedule.Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
S6PNJ said:
We've got similar, but I turned it off shortly after having it installed (about 2 months) as I couldn't understand how it worked and sensed. I bought a Grundfos UP 15-14BA PM(80) Brass Comfort Hot Water Circulator Pump with Auto Adapt which does what you say - senses the temp rise when the 'call for hot water' is demanded, then learns from that - but if it learns that I need hot water at 7:00am but am then away for a few weeks, then at 7:00am the pump starts circulating and the temp sensor senses the heat flow which re-enforces the schedule - so how does it ever learn a new schedule.
Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
Do you have any idea how much more it costs on gas on days when you run the pump v.s. not?Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
DayZer0 said:
S6PNJ said:
We've got similar, but I turned it off shortly after having it installed (about 2 months) as I couldn't understand how it worked and sensed. I bought a Grundfos UP 15-14BA PM(80) Brass Comfort Hot Water Circulator Pump with Auto Adapt which does what you say - senses the temp rise when the 'call for hot water' is demanded, then learns from that - but if it learns that I need hot water at 7:00am but am then away for a few weeks, then at 7:00am the pump starts circulating and the temp sensor senses the heat flow which re-enforces the schedule - so how does it ever learn a new schedule.
Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
Do you have any idea how much more it costs on gas on days when you run the pump v.s. not?Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
S6PNJ said:
We've got similar, but I turned it off shortly after having it installed (about 2 months) as I couldn't understand how it worked and sensed. I bought a Grundfos UP 15-14BA PM(80) Brass Comfort Hot Water Circulator Pump with Auto Adapt which does what you say - senses the temp rise when the 'call for hot water' is demanded, then learns from that - but if it learns that I need hot water at 7:00am but am then away for a few weeks, then at 7:00am the pump starts circulating and the temp sensor senses the heat flow which re-enforces the schedule - so how does it ever learn a new schedule.
Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
This is how I feel - I have looked for tips on practical usage but all I can find is the manufacturer's propaganda, thus it is "essential" Oh and the fact that our schedule is not very 'schedule like', so every day is different pretty much, so a big waste of money for me.
Yeh mines one of those Grundfos Auto Adapts. It apparently learns a 2 week cycle and would carry on refining that if things change. It kinda works for us at the moment as I work alternate weeks at work meaning I get up at 5:30 every other week and there's always hot water straight away for my shower, but what I don't know if how much/often it pumps in order to achieve that, does it do it 5 minutes before I get up or is it running half the night in preparation? 
paulrockliffe said:
Doesn't really need to be particularly clever, my burglar alarm will spin up a pump for 60s if it detects someone in the bathroom with just a little wiring to a relay and some changes in the settings.
This is all you really need - motion trigger the system when it's likely to be needed. Predictive systems just add unnecessary complexity to a simple problem, and running continuously or based on temperature is just a waste. Obviously decent insulation is a good plan too, so not just 13mm polyethylene.
I don't think that anyone has mentioned a thermostat on the return pump.
Some pumps have no timer or thermostat, some just a timer and some have both.
With this setup you can set a timer and when the water returning to the cylinder reaches the preset temp, the pump will switch off. The pump only runs for a few seconds or so depending on the length of the run.
Some pumps have no timer or thermostat, some just a timer and some have both.
With this setup you can set a timer and when the water returning to the cylinder reaches the preset temp, the pump will switch off. The pump only runs for a few seconds or so depending on the length of the run.
This is interesting, we had our system updated and the old secondary return pump was seized and thus replaced. New one is on a timer only, runs an hour in the morning and an hour in the evening (told that continuous running would be inefficient and trigger the boiler occasionally).
Is this going to be expensive, and what would happen if we simply stopped using it (other than having cold water run off obviously)?
Is this going to be expensive, and what would happen if we simply stopped using it (other than having cold water run off obviously)?
LocoBlade said:
There's not really any point in it running for an hour twice a day because the water in the pipes will be cold within 30 minutes of it stopping, then you're back to the same situation of not having it in the first place.
The idea is it runs during peak time (breakfast and washing up after dinner essentially), running it all day for the odd hand wash in the downstairs loo seems pretty wasteful if they cost a bit to runGassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff