@jamespa Yes, that's what we both said above I believe. When the pump is running in my case (for four hours in the morning, not constantly or 24x7) it has to displace the cold water in the pipes and replace it with warm water so its instant hot water. Without the recirc pump, I need to heat the DHW to mid-50's to have a warm shower; with the pump on, I only have to heat it to mid-40's and its warmer at the tap. If there's less hot water in the tank after a recirc cycle (4 hrs in the morning, and 20 mins in the evening for my son's showers after football when I turn it on and off manually) I can live with that as we don't have any demand for hot water between these events, and there is a DHW cycle at lunchtime to top back up (to mid-40's). As I say, compared to the consumption related to space heating, its all a minor thing.

Posted by: @marzipan71

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@jamespa Yes, that's what we both said above I believe. When the pump is running in my case (for four hours in the morning, not constantly or 24x7) it has to displace the cold water in the pipes and replace it with warm water so its instant hot water. Without the recirc pump, I need to heat the DHW to mid-50's to have a warm shower; with the pump on, I only have to heat it to mid-40's and its warmer at the tap. If there's less hot water in the tank after a recirc cycle (4 hrs in the morning, and 20 mins in the evening for my son's showers after football when I turn it on and off manually) I can live with that as we don't have any demand for hot water between these events, and there is a DHW cycle at lunchtime to top back up (to mid-40's). As I say, compared to the consumption related to space heating, its all a minor thing.

All noted and recognised.  Your response actually prompts me to break it down into two separate effects:  

1. The circulating pump, by creating continual movement in the tank, will likely reduce stratification.   So whereas, without circulation, you can continue to draw off hot water from the top of the tank even though the bottom has cooled, with circulation it is less likely you can do this because the constant movement means there may (will?) be more mixing.  Thus the amount of usable hot water stored is reduced even if there are no losses in the pipework.

2. The fact there is hot water in the DHW pipes constantly, because its circulating constantly, inevitably means that heat will be lost from the pipes to the surroundings depleting the energy stored in the system and thus the temperature of the water.

Unfortunately both these effects act against us.  In a very well insulated house where the occupants use a lot of DHW I could imagine this is a significant part of the energy consumption (and a significant problem in summer).  In a more average house it will, as you say, be a minor thing.

@jamespa Yes I'm sure you're right. As I say, I'd like to replace the mechanical DIN rail timer with a wifi & Alexa controlled version - that way, the recirc pump will be in a default off state. I can then tell Alexa to turn it on immediately before my shower (it reacts almost instantly at the shower, as I mentioned) then off after my wife's shower - so in total 30 mins, no more. 10 mins for my son's shower in the evening. That way it won't be recirculating for its current 4 hrs in the morning. I'm not sure I'd even be able to detect the effects of the recirc pump in that case in terms of electrical consumption (related to the DHW, not the pump which uses nothing) - and anyway, it will be at least partially offset by the reduced electrical consumption due to heating the DHW to mid-40's rather than mid-50's which my AI assistant tells me is 'huge' (caveat - it talks rubbish half the time). You'd have to tear my recirc pump from my cold, clammy hands at this point. I do think just turning it on on-demand is the way forward - where the internet always assumes its on 24x7 or whatever.

@johnnyb Hopefully this will inform your decision.  @marzipan71 @jamespa have captured my issue in a nutshell.  Have the timer set for your "known" requirements in the mornings such as showers, washing up etc. And then just manually switch on as required for the rest of the day....my lot have got use to it....eventually.

Posted by: @ngillam

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@johnnyb Hopefully this will inform your decision.  @marzipan71 @jamespa have captured my issue in a nutshell.  Have the timer set for your "known" requirements in the mornings such as showers, washing up etc. And then just manually switch on as required for the rest of the day....my lot have got use to it....eventually.

Exactly, yes. Now if my shower valve was internet-connected, and I had a WiFi recirc pump switch on the DIN rail, I could have the recirc pump start and stop for those on-demand family showers. Our rain shower heads are 10 litres per minute so three showers a day are far and away the biggest consumers of hot water.

Posted by: @marzipan71

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Posted by: @ngillam

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@johnnyb Hopefully this will inform your decision.  @marzipan71 @jamespa have captured my issue in a nutshell.  Have the timer set for your "known" requirements in the mornings such as showers, washing up etc. And then just manually switch on as required for the rest of the day....my lot have got use to it....eventually.

Exactly, yes. Now if my shower valve was internet-connected, and I had a WiFi recirc pump switch on the DIN rail, I could have the recirc pump start and stop for those on-demand family showers. Our rain shower heads are 10 litres per minute so three showers a day are far and away the biggest consumers of hot water.

 

Better still if the pump had extra-sensory perception and could read your thoughts in advance so it could turn itself on at just about the right time.

Alternatively, just wait a minute for the water to come through!

Ha ha yes - fair point. I was referring not to the gap between the hot water arriving (and without my pump it's 4 minutes for hot water to arrive - or 120 litres of wasted water a day across 3 showers, which is significant - 300 sq m single storey house) but more the behavioural change when you have a family and tell them that they need to open up a fuse box to access the DIN rail to switch on a timer thing before taking a shower. Of course, that's my job. Serious point being if the valve could send a signal to the pump it would mean there was no change in behaviour or explanation needed - other than the positive change of instant hot water instead of waiting around wasting water twiddling thumbs. In my house, when my son wants to take a shower my wife ends up calling me from my office saying 'Can you turn on the shower thingy?'. If we had to do something similar every time we wanted to flush a toilet there would soon be a solution, if you see what I mean. 

Well, I guess I will see how it goes, but it does sound like the pump is a 'nice to have' but needs using a little carefully if it isn't going to cool the tank quicker than it should be. My pipes are insulated with the thicker grey pipe insulation and I have loft roll inbetween the joists for sound insulation.

My family are used to strange things with the hot water and having cool or cold showers occasionally when the DHW timings don't work if someone uses extra hot water. That's one of the main reasons for fitting a 300ltr tank, I expect to only heat the tank once a day when electric is cheap.

My understanding is if the pump isn't switched on we still get hot water the same as if there wasn't a pump but if it is switched on the hot water is there nearly instantly, there isn't a negative to having a pump as I can leave it switched off or just switch it on when needed. After reading this thread I am trying to work out if I can still get cables to the bathrooms to switch the pump on when we need a shower, or get a wireless switch/switches.

If I only switch the pump on for morning showers then I don't expect the heat loss to be too much higher. We currently have to run the shower for 30 seconds or so to get hot water and it cools down quite quickly so unless we shower immediatly after each other, which rarely happens, we are starting again. If I can have it so we switch the pump only when we are about to use the bathroom and only need to turn the shower on as we get in it there may not be too much difference and there will be less wasted water.

@jamespa our hot water flow and return pipe fittings are both at the top of the tank. Unless one has a pipe running down the inside of the tank I don't think there will be much mixing.  

New houses often have extra bathrooms/ensuites that older houses weren't designed with. Our main bathroom has the shower directly above the hot water tank and will have nearly instant hot water anyway but our ensuite is further away. I had mentioned waiting for hot water in our current house to the plumbers and they are fitting a pump without me even realising it was part of the quote.

Posted by: @johnnyb

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@jamespa our hot water flow and return pipe fittings are both at the top of the tank. Unless one has a pipe running down the inside of the tank I don't think there will be much mixing.  

Noted.  That will probably help but does of course mean that the water which was piping hot at the top is returned to the top slightly cooler, as a result of being circulated.

Posted by: @johnnyb

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My understanding is if the pump isn't switched on we still get hot water the same as if there wasn't a pump but if it is switched on the hot water is there nearly instantly, there isn't a negative to having a pump as I can leave it switched off or just switch it on when needed

Thats my understanding also but someone reported otherwise, for reasons I haven't yet understood.  Try it and see, which doubtless you have already done!

Posted by: @johnnyb

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My understanding is if the pump isn't switched on we still get hot water the same as if there wasn't a pump but if it is switched on the hot water is there nearly instantly, there isn't a negative to having a pump as I can leave it switched off or just switch it on when needed. After reading this thread I am trying to work out if I can still get cables to the bathrooms to switch the pump on when we need a shower, or get a wireless switch/switches.

Yes, this is how it works. As I mentioned above, our water is now heated to mid-40's and arrives at that temp at the shower head, where without the recirc pump we had to heat the water to the low or mid-50's (depending on time of year) and it would arrive more or less mid-40's at the shower head. So in my book that's a big saving on heating the water, plus the water saving of not waiting for the shower to heat up (100 litres or more per day). My current DHW usage grid consumption is around 5kwh per day; space heating is around 20-50kwh depending on solar and OAT, so comfort trumps other considerations for me. Don't judge.

I've just today started my trial though of heating the water to 58C at lunchtime (max solar) and hoping (well, AI calculated it for me) that it should be around mid-40's by 6am the next day, given evening usage for my son's shower and general domestic use; this should elminate my 5am DHW cycle which in the absence of solar and with the system being cool spikes at 6kwh.

My ramblings about the shower valve being wifi connected - you made me think @johnnyb that it might be possible to install a switch either in a spare slot in my wall switch or a wireless switch that could tell a digital timer (rather than the mechancial timer I currently have) to swtich on or off. Would need one in my son's bathroom also. I'm not in any way electrical so not sure if that exists but my experience is that if you can imagine something wifi or smart, it probably exists.

Good luck!

@marzipan71 Wouldn't it be good if the light/extractor fan switch could be linked to the pump.....nobody showers in the dark.

Posted by: @ngillam

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@marzipan71 Wouldn't it be good if the light/extractor fan switch could be linked to the pump.....nobody showers in the dark.

Ah but you do pee with the light on (I assume) and I don't need the recirc pump when I'm peeing. Extractor fan might work yes unless its one of those humidity sensing ones. Of course all this falls apart when I try to tell my 10 year old to turn on an extra switch when he's showering - extractor fan, recirc pump, towel radiator...