Best spec for high pressure hot water to multiple outlets?

[sendu]

I'm doing a renovation and want the best possible hot water pressure to multiple outlets simultaneously, eg. up to 3 showers running at once, or shower plus washing machine plus kitchen tap etc. It's a 5 bed with 2 en-suite and 1 family bathroom.

 

Am I right in thinking that a high-spec system boiler with a "tank-in-tank" is best way to go? Any recommendations for these? Could such a system give effectively unlimited hot water if the boiler is powerful enough?

 

Is it worth getting rid of all existing hot water pipes and re-doing the plumbing with a view to maintaining high pressure to all outlets in the house?

 

Does it make any significant different where the boiler, tank and main outlets are in relation to each other? Can I have boiler and tank next to each other in the bottom left corner of the house, and the family bathroom in the top right corner of the house?

[Alister84]

Id be interested to know if you found a good solution to this @sendu . Planning our new build and demand for hot water is near constant with multiple bathrooms and teenagers.

[Temp]

If it's a restoration using an existing mains supply  you need to start by checking both the pressure and the flow rate from the mains is adequate for what you want. If not then you may need to get it upgraded. The performance of the mains supply may partly dictate the best solution. 

 

If you had to heat the water instantly (like an electric shower or combi boiler does) the power required might be 10-12kW per shower. So three showers and some left over would likely need a 40kW+ boiler to run indefinitely but is that really necessary?

 

When we built our house one company proposed a solution using two boilers. We didn't go down that route in the end but can see it might make sense in some situations, for example in a large house with showers far apart it might make sense for one to be a combi boiler feeding one of the showers. 

 

We ended up with a thermal store fitted with two heat exchangers. Give us mains pressure hot water everywhere. Down side is it leaks quite a lot of heat into the room it's in.

[Adsibob]

I’m interested in reviving this thread as I have a similar query, in that I am also gutting and replumbing a 5bed property with three bathrooms. I’m not so worried about an endless supply of hot water, as I think a 250L cylinder will be enough (and I would imagine 300L would be enough for @sendu since bathing water is much cooler than cylinder water so once it’s mixed with cold water, a 300L cylinder of hot water could provide for several baths and even more showers). My concern is more about the long run of pipes making the time it takes for hot water to travel from the cylinder to the outlet as much as a 12m distance for some outlets, most of which is upwards against gravity. 

A solution that has been suggested to me for this is to have a whati think it’s known as a primary circuit which essentially continuously or intermittently (depends on the setup) circulates hot water to the outlets before the tap is turned on so that the water is waiting for you. There are two ways I’ve been told about how this can be achieved: with PIR motion sensors that activate the circuit when one approaches the outlet, or a less sophisticated solution which continuously runs the water around the circuit with a pump during waking hours. Still investigating which one suits me best: 

My main concern about the PIR activated system is that it is possibly more likely to go wrong, but I’m not basing that on any evidence. It’s just a gut instinct. It’s more expensive to install, but it should save slightly on running costs/heat loss vs the pump.

 

My main concern about the pump is noise. I hate house sounds, particularly pumps.

 

If anyone could comment about either  system and their pros and cons, that would be really helpful.

[Temp]

1 hour ago, Adsibob said:

A solution that has been suggested to me for this is to have a whati think it’s known as a primary circuit which essentially continuously or intermittently (depends on the setup) circulates hot water to the outlets before the tap is turned on so that the water is waiting for you.

 

Its called a Secondary Loop. The primary circuit 8s boiler to tank. Secondary is tank to taps.

 

We have a secondary loop. They key is to run the loop as close to the tap as possible. In our WC the plumber T'd off about 3m from the loop to the tap which means most people are done washing hands before the hot water arrives so the loop is ineffective in that WC.

[Dave Jones]

On 17/02/2020 at 10:37, sendu said:

I'm doing a renovation and want the best possible hot water pressure to multiple outlets simultaneously, eg. up to 3 showers running at once, or shower plus washing machine plus kitchen tap etc. It's a 5 bed with 2 en-suite and 1 family bathroom.

 

Am I right in thinking that a high-spec system boiler with a "tank-in-tank" is best way to go? Any recommendations for these? Could such a system give effectively unlimited hot water if the boiler is powerful enough?

 

Is it worth getting rid of all existing hot water pipes and re-doing the plumbing with a view to maintaining high pressure to all outlets in the house?

 

Does it make any significant different where the boiler, tank and main outlets are in relation to each other? Can I have boiler and tank next to each other in the bottom left corner of the house, and the family bathroom in the top right corner of the house?

 

looking at similar, its looking like dual combi boilers and a couple of tanks feeding the bathrooms with various pumps. The combi's can keep the tanks red hot irrespective of demand.

Edited January 16, 2021 by Dave Jones

[PeterW]

7 minutes ago, Dave Jones said:

 

looking at similar, its looking like dual combi boilers and a couple of tanks feeding the bathrooms with various pumps. The combi's can keep the tanks red hot irrespective of demand.

How are you storing heated DHW from a combi..? Or are you suggesting that you use the heating circuit to keep a local tank hot and then replenish it from the combo flow when it kicks in ..??

 

5 hours ago, Adsibob said:

replumbing a 5bed property with three bathrooms. I’m not so worried about an endless supply of hot water, as I think a 250L cylinder will be enough

Not likely at all. A 250 litre tank at 60°C holds around 330 litres of shower temperature water when blended down. That’s around 14 minutes for a pair of showers running together before the tank is cold. In a 5 bed/ 3 bath I would recommend 400 litres in a UVC. Anything smaller and you will need a bigger system boiler with a higher output to keep up with usage. 
 

5 hours ago, Adsibob said:

intermittently (depends on the setup) circulates hot water to the outlets before the tap is turned on so that the water is waiting for you. There are two ways I’ve been told about how this can be achieved: with PIR motion sensors that activate the circuit when one approaches the outlet, or a less sophisticated solution which continuously runs the water around the circuit with a pump during waking hours.

Secondary circulation loop would work here but you need to design in the outlets too - which need hot water “instantly” and which can wait. If you go the traditional route of running large bore to the bathrooms and then tee off from this for the shower / basin / bath you need to get the return as close to the basin as possible as otherwise the response time will be too slowed @Temp points out.  Baths and to a point showers are less of an issue due to the volume of water involved, so consider a secondary loop run in 10mm that only serves the basins and kitchen / utility tap as that will be more than adequate. We changed a permanent running install to one that ran 5 minutes every hour in a commercial building and reduced the water heating costs by £100/yr using a £20 timer. A well insulated pipe doesn’t lose that much heat and usage will also ensure it stays hot. 
 

 

[Temp]

5 hours ago, Dave Jones said:

 

looking at similar, its looking like dual combi boilers and a couple of tanks feeding the bathrooms with various pumps. The combi's can keep the tanks red hot irrespective of demand.

 

 Did you mean a system boiler? It is possible to use a combi boiler to heat a tank (there are even some advantages) but its not a very common thing to do.

 

With a combi the CH circuit gets a diverter so the CH side can heat both the CH and a DHW tank. The tank is used for high flow rate outlets like showers. The DHW side of the boiler can still be used or low flow rate outlets like taps or dedicated to one shower.

Edited January 16, 2021 by Temp

[Adsibob]

7 hours ago, PeterW said:

12 hours ago, Adsibob said:

replumbing a 5bed property with three bathrooms. I’m not so worried about an endless supply of hot water, as I think a 250L cylinder will be enough

Not likely at all. A 250 litre tank at 60°C holds around 330 litres of shower temperature water when blended down. That’s around 14 minutes for a pair of showers running together before the tank is cold. In a 5 bed/ 3 bath I would recommend 400 litres in a UVC. Anything smaller and you will need a bigger system boiler with a higher output to keep up with usage. 

Thanks @PeterW. I was thinking of having the tank temperature set higher than 60°C, maybe 64°C or even 65°C. My understanding is that anything hotter risks scalding but actually where we're living at the moment the tank temperature is set to 67°C and it only really approximates scalding if you leave your hand there for a bit too long, but that could be because this is an old ground floor Victorian mansion flat with poor/zero insulation. The tank is about 20 years old and doesn't look very well insulated and no idea about the pipes being insulated, so maybe by the time the water gets to the outlet it's dropped to 66°C. My point being, 64°C or 65°C should generate quite a bit more bathing water than the 330litres you suggest I could get from a 250 litre tank.
The reason I'm concerned about a 400 litre tank is partly space considerations and partly heat loss, which will be greater than 250 litres. I'm not sure i have space for a 300 it depends whether it needs an air gap around it or whether it can go right up against a wall. The space it is meant to be going into is 1750 wide (assuming the builder's accuracy is good - as this space hasn't been built yet!) and I've just checked the Telford Tempest 300L horiz. indirect unvented cylinder is 1650 wide, so that leaves 100mm to spare, so 5cm either side. Is that enough?  

 

According to tradeplumbing.co.uk they recommend:

 

1 Bedroom Property + Shower & Bath - 75/120 (indirect) or 120/150 (direct)

2 Bedroom Property + Shower & Bath - 150 (indirect) or 180 (direct)

3 Bedroom Property + Shower & 2 x Bath - 180 (indirect) or 210 (direct)

4 Bedroom Property + Shower & 2 x Bath - 210/250 (indirect) or 250/300 (direct)

LARGE Properties - 300+ (indirect) or 300+ (direct)

 

So I guess you are right that 250 may not be enough, but 400 really seems excessive. Surely a 300 indirect set at 64°C or 65°C will be enough?

 

[PeterW]

5 minutes ago, Adsibob said:

My point being, 64°C or 65°C should generate quite a bit more bathing water than the 330litres you suggest I could get from a 250 litre tank.

not really - you’ll get another 25 litres at best, so an extra minute per shower. 

 

29 minutes ago, Adsibob said:

where we're living at the moment the tank temperature is set to 67°C and it only really approximates scalding if you leave your hand there for a bit too long,

 

You’re not getting 67°C to the taps if you can put a hand under it as that is enough to scald within 3 seconds. I expect your settings are as accurate on the tank and it’s closer to 55°C and also is losing heat if it’s an older smaller tank due to fluid turbulence. 
 

It is best practice (and a legal requirement for a bath) to install mixing valves or TMVs on baths and ideally all hot water from an unvented cylinder. 
 

31 minutes ago, Adsibob said:

The reason I'm concerned about a 400 litre tank is partly space considerations and partly heat loss, which will be greater than 250 litres.

So the heat loss in 24 hours from a 250 is 2.16kW, from a 300 it is 2.32kW and a 400 it is 2.58kW so not worth even considering 

 

33 minutes ago, Adsibob said:

The space it is meant to be going into is 1750 wide (assuming the builder's accuracy is good - as this space hasn't been built yet!) and I've just checked the Telford Tempest 300L horiz. indirect unvented cylinder is 1650 wide, so that leaves 100mm to spare, so 5cm either side. Is that enough?  

Why horizontal ..?? A vertical cylinder needs 710mm, and you can get all the pipe work within the 10-2 area on the front of a tank as all Telford cylinders are built to order. That would fit in a space 800mm wide,  the 400 has a 40 litre expansion vessel that can be mounted above it and the whole lot is only 2.1m tall including the expansion. 
 

35 minutes ago, Adsibob said:

According to tradeplumbing.co.uk they recommend....

If I specified a 120 litre tank for a flat where it would drain it dry with a 10 minute shower I would be crucified ... 

 

Price differential between 250 - 300 - 400 is about £35-40 each time so it’s not costing that much more in the scheme of things to install a decent hot water system. 
 

Is this boiler or ASHP out of interest ..?

[AliG]

I have a 500L UVC but set it to only 50C, I can turn it up if we have a lot of people staying.

 

It came from this company, as you can see from the specs it takes time to reheat a tank and all the time you are diluting the water temperature down. The Telford 300L cylinder says 29 minute reheat from 75% draw off so similar to the numbers below. An UVC cannot take the full 40kW output of a large boiler usually, so you cannot just add a bigger boiler to heat it up faster.

 

A couple of simultaneous 10 minute showers at 40C are going to use around 150L of 64C water. So your tank would need around half an hour to reheat. If you draw 150L of water from a 250L cylinder at this time of year when the water temp is only maybe 4 or 5C then you are going to reduce the temperature in the cylinder to around 30C The water will be heating up as you draw it out, but a 250L cylinder would struggle to hold 40C for the duration of 2x10 min simultaneous 10L/min showers. It would be at around 37C when the showers were over. A 300L tank on the other hand would only see a drop to 35C as you are using less of its capacity. Thus including the heating capacity it can hold the temperature over 40C for the same two showers.

 

The issue then is what if someone comes along to have a third shower. You would only have to wait around 5 minutes for the 250L to be back at 40C. But if you start with the temperature at 40C, by the time you are finished it would be 26C, again the boiler is running, so it would actually end up at around 33C. To be able to have a shower you need a starting temperature in the low 50s in a 250L tank and 50C in a 300L tank so either tank would need close to 20 minutes to heat up after 2 showers before you should start another one.

 

From these numbers basically a 250L tank would struggle to hold the temperature above 40C for two simultaneous long showers or a bath and a shower. A 300L would do it more comfortably. Neither tank is going to have enough hot water for 3 simultaneous showers. This is why I went to 500L as 3 simultaneous showers or a bath and 2 showers was my target. We often have a lot of people staying.

Edited January 16, 2021 by AliG

[Adsibob]

1 hour ago, PeterW said:

Why horizontal ..?? A vertical cylinder needs 710mm, and you can get all the pipe work within the 10-2 area on the front of a tank as all Telford cylinders are built to order. That would fit in a space 800mm wide,  the 400 has a 40 litre expansion vessel that can be mounted above it and the whole lot is only 2.1m tall including the expansion. 

I don't have space for a vertical one. It's beneath some eaves in an alcove which would otherwise be unusable and that alcove is a great location becaise it's very close to two of the baths and not too far to the third - although given I'm plumbing in a secondary loop, maybe distance from tank to the outlets is irrelevant? In that case, a vertical tank could go in some of the loft space, although that does mean making my fifth bedroom (which is in the loft conversion) slightly smaller. But I was pretty happy with the location of the horizontal tank.

Maybe the solution is to make one of the showers electric and just plan better if we want baths more regularly. Not ideal really.

[Adsibob]

2 hours ago, PeterW said:

Is this boiler or ASHP out of interest ..?

Current thinking is to with a Veissman Vitodens 200W gas  boiler, though I haven't figured out whether to get 30kw or 35kw model. Any thoughts?

 

I originally wanted a ground source heatpump but our garden isn't big enough for a horizontal layout and to get the bore holes drilled for a vertical set up was apparently impossible because our driveway wasn't big enough for the drilling rig.  Mine is about 40 sq metres but apparently that's not big enough, based on enquiries with four different drilling companies. I don't understand why there isn't a company which can liaise with the local council to temporarily annex the pavement so that they can use that together with the driveway space for the rig. I'm very much into renewable energy, but in London where space is cramped ground source just is not realistic unless you can crane the rig over the house into your back garden!

 

For air source, these aren't as efficient as ground source, and given how noisy and unsightly they can be, the need for planning permission (at least in my borough), it didn't seem worth it. One exception was an impressive Austrian made Ochsner air source heat pump which was some sort of table system that also drew heat from rainwater as well as air. It was quiet enough and possible to install in the back garden where it wouldn't need planning permission. But the supply and installation was coming to around £20k and it would have also made our utility room quite a lot smaller because of the rather large sized compressor. They also didn't have as good warranties as the Veismman and the annual service was more expensive too. These prices are just not really realistic and it's frustrating the government has not done more to incentivise advances in this type of technology or make it easier to drill bores in your front drive/yard.

[AliG]

Either 30 or 35kw boiler should be fine.

 

As you are tight for space the way to effectively increase the size of your tank is to run it hotter. You can fill it with 75C water and then have a mixer valve that minimises the temperature coming to the taps.

 

15mm copper pipe holds 0.14L per metre and 22mm holds 0.31L per metre. Plastic pipe has thicker walls so is a bit less. So a 12M 15mm pipe would hold around 1.5L of water. Assuming a shower at 10L/min it would take around 10 seconds for 15mm pipe to run hot and 20 seconds for 22mm pipe. I wouldn't worry about it. Gravity shouldn't have any impact as long as you have enough water pressure.

 

I have a circulating water circuit as my longest pipe run is over 30M and there was nowhere else to put the tank. They waste a lot of energy if you leave them running all the time. I just run it 4 times a day. It is like having a radiator that is hot in your house 24hours a day 365 days a year and I would recommend trying to minimise the amount water in the pipes instead which reduces losses and speeds up the water getting to the tap. 

[Adsibob]

36 minutes ago, AliG said:

Either 30 or 35kw boiler should be fine.

Given the price increase to a 35kW is pretty minimal and the Veissman is known to have excellent modulating properties, I think it makes sense to go with the larger output.

[Adsibob]

42 minutes ago, AliG said:

Either 30 or 35kw boiler should be fine.

 

As you are tight for space the way to effectively increase the size of your tank is to run it hotter. You can fill it with 75C water and then have a mixer valve that minimises the temperature coming to the taps.

 

15mm copper pipe holds 0.14L per metre and 22mm holds 0.31L per metre. Plastic pipe has thicker walls so is a bit less. So a 12M 15mm pipe would hold around 1.5L of water. Assuming a shower at 10L/min it would take around 10 seconds for 15mm pipe to run hot and 20 seconds for 22mm pipe. I wouldn't worry about it. Gravity shouldn't have any impact as long as you have enough water pressure.

 

I have a circulating water circuit as my longest pipe run is over 30M and there was nowhere else to put the tank. They waste a lot of energy if you leave them running all the time. I just run it 4 times a day. It is like having a radiator that is hot in your house 24hours a day 365 days a year and I would recommend trying to minimise the amount water in the pipes instead which reduces losses and speeds up the water getting to the tap. 

So are you saying that if my maximum pipe run from tank to outlet is about 12M, I shouldn't bother with a secondary loop because the extra heating costs are not worth the time saving? I find that a little bit surprising because the property I'm renting at the moment (not the house I'm re-doing) has pretty good water pressure, with a Megaflo Heatae Saedia CL250 tank about 13M or maximum 15M from the bathroom and the outlets in that bathroom take quite a bit longer to heat up: the first use of the day will take about 30 seconds to get warm and 40 seconds to get hot. That is with turning the tap on full (which results in more water than one would normally need to wash your hands). But the problem isn't just limited to the basin, in that when I'm in the bath, say I want to add more hot water after 20 minutes or so, I need to endure 20-30 secs of cold water first. Obviously I don't know how this was set up, and maybe the pipe runs are not direct, but that would be surprising as everything is on the same floor (it's a ground floor flat) with the tank at one end of the corridor and the bathroom at the other. There is actually a grunfos pump by the side of the heatrae megaflo that is not currently switched on. The landlord said I could switch it on if I wanted to but I've not yet experimented. It's right by our bedroom and the Mrs is sensitive to sound.

[Adsibob]

1 hour ago, AliG said:

As you are tight for space the way to effectively increase the size of your tank is to run it hotter. You can fill it with 75C water and then have a mixer valve that minimises the temperature coming to the taps.

That's an interesting idea @AliG. Is that one mixing valve per outlet, or just one for the whole system? Why doesn't everybody do this and fit a smaller tank? there must be a downside, like increased running costs.

[AliG]

A larger tank would be cheaper than a TMV and a TMV has moving parts so can break. I think they also may limit the flow or pressure available.

 

There are various regs that affect the installation of these so it’s not always possible. You’d need someone who knows more about plumbing than me.

Seems like a Horne TMV2 is a well respected valve for this purpose. 

 

[PeterW]

There is a legal requirement for a bath to be fitted with a TMV3, or the supply limited to below 48°C and I have seen BCOs check this. 
 

The quickest and easiest way to do this is blend the whole system from the UVC at the outset. It is easy to do, and they aren’t expensive. I usually specify Reliance TMVs as they are maintainable. You will comfortably get 35 litres/min through which is more than enough for two or more showers running simultaneously. 
 

The other  issue with higher temperatures is higher standing losses, and in certain circumstances you will loose the efficiency of condensing on the boiler. 
 

 

[PeterW]

3 hours ago, Adsibob said:

Current thinking is to with a Veissman Vitodens 200W gas  boiler, though I haven't figured out whether to get 30kw or 35kw model. Any thoughts?

I’m sure there is an offer on Veissman in Wolseleys at the moment as this is the second question about these this week ..!

 

Rule on boilers is simple - how many installers can you find to install it is one thing, but what about service and maintain it ..? Lots of PHEs do Worcester Bosch, Baxi, Ideal and Vaillant. They reduce quickly when you go down to Vokera, Alpha and Veissman so when it goes wrong who can you call ..?

 

Are you having UFH or rads ..?

 

 

 

 

 

[Adsibob]

18 minutes ago, PeterW said:

Rule on boilers is simple - how many installers can you find to install it is one thing, but what about service and maintain it ..? Lots of PHEs do Worcester Bosch, Baxi, Ideal and Vaillant. They reduce quickly when you go down to Vokera, Alpha and Veissman so when it goes wrong who can you call ..?

 

Are you having UFH or rads ..?

Yeah, I see where you are coming from, but I’m pretty fed up of Vaillants - I’ve had problems with two of their combi boilers. I like the Tado thermostats, and they talk directly to Veissmans without needing extra kit. Veissman also rated highly by which magazine.

 

Apart from towel heater rads in the bathrooms, we are planning to have about 9 zones of UFH throughout the ground and first stories and then haven’t decided about the loft. It was going to be rads there, but might get away with no heating in the loft, or just some undersized rads. Why do you ask? 

[PeterW]

So a big boiler and UFH will need a buffer tank or it will short cycle. Does theTado do multiple zones for UFH or does it just do one or two zones...?

[Adsibob]

5 minutes ago, PeterW said:

So a big boiler and UFH will need a buffer tank or it will short cycle. Does theTado do multiple zones for UFH or does it just do one or two zones...?

What’s a buffer tank? Is that the same as an expansion vessel? I’minstalli g a low loss header as well, as I thought that would make the boiler more efficient. 

 

Tado is just a smart thermostat that can be controlled from anywhere in the world and that can use geofencing so that your standard routine is switched off when you leave your house, meaning you never forget to switch the heating on. It then switches back to “home mode” when you return to within x distance of your house - you can set x. 
 

so each zone will need its own thermostat. So I will need 9 tados. Expensive, but amazon do good deals on them whenever there is an amazon prime day or Black Friday sale. I will put my existing Tado TRV valves from my old radiator setup onto the towel rads in each bathroom, and then I can add those to the routine. It’s really a wonderful setup. When we installed them in our old house we saved a third on our heating bill. Also really good during winter if you unexpectedly return home, as you can switch your heating in on during the journey home. 

[Dan F]

 

15 hours ago, PeterW said:

In a 5 bed/ 3 bath I would recommend 400 litres in a UVC. Anything smaller and you will need a bigger system boiler with a higher output to keep up with usage. 

 

Or use 300 liter + WWHRS.  The WWHRS means (depending on system used) that the cold water is closer to 28C than 10C, meaning the water in your UVC goes a fair bit further.  

 

6 hours ago, AliG said:

it takes time to reheat a tank and all the time you are diluting the water temperature down.

 

There are couple of approaches/products that are supposed to mitigate this dilution issue and improve hot-water availability.  

- https://www.mcdonaldwaterstorage.com/products/plateflow-plate-heat-exchanger

- https://www.mixergy.co.uk/

 

21 hours ago, Adsibob said:

My main concern about the PIR activated system is that it is possibly more likely to go wrong, but I’m not basing that on any evidence. It’s just a gut instinct. It’s more expensive to install, but it should save slightly on running costs/heat loss vs the pump.

 

You can get pumps than recirculate based on temperature and can even "learn" usage patterns if you want to avoid PIR''s.   I'm not sure I'd worry about the noise, if you've ever lived in a house with central heating there is a pump pumping the water around.  https://product-selection.grundfos.com/products/comfort

 

 

[PeterW]

27 minutes ago, Dan F said:

 

There are couple of approaches/products that are supposed to mitigate this dilution issue and improve hot-water availability.  

- https://www.mcdonaldwaterstorage.com/products/plateflow-plate-heat-exchanger

Cost of a plate flow with buffer - and finding the space for another 200 litre tank - you may as well put a bigger tank in in the first place. 
 

And waste water heat recovery only works with showers - it doesn’t work with baths which is a serious limitation. 
 

As I said, min 400 litres in a house that size as for the £75 difference it’s just not worth the hassle.