Boilers... Hot water... What are best options

[rexehuk]

I'm currently redoing a town house, as part of this we're turning the main bathroom into a wet room with thermostatic shower (high pressure would be nice).

Currently, we have a Valiant ecoTEC Plus 418, with an indirect 117 litre cylinder. Both of these are located on the ground floor, part of a conventional system so header tank/expansion in the loft.

Our wet room will be on the 2nd floor, kind of straight line from the cylinder with slight offset. The total distance from cylinder to bathroom floor straight up is around 4.8M, adding another 2m if you consider the spout height in bathroom would be from ceiling or top of wall dependant on shower choice.

Now, with 117 litre cylinder we're expecting a short shower... and are worried about it providing 2 showers every morning lasting say 20 minutes a piece. Not only that, if we have guests it would be nice to have 4-5 showers in succession.

The only testing we've done thus far is flow, and we're achieving at the moment 10 litre/minute on hot and cold feeds independently. I thought that was fairly good, as it's pushing up 2 floors and from what I can tell no hot water/shower pump fitted. Is this likely however to deliver a nice powerful shower?

What options are open to us? All of the pipe work is currently exposed... but can the existing hot water cylinder be swapped out for something like a megaflow?

Any help would be much appreciated! Boiler systems still miff me, despite learning a ton by doing the house. Would be great to get the options on the table, as well as any concerns I have confirmed.

 

[Skillmister]

20 minute showers

 

[Participant]

Your options can't be determined from the information provided.

On the face of it, 10L/min flow is absolutely insufficient for an unvented system and would deliver a shower akin to an electric shower, let alone if someone flushes a toilet or runs a tap elsewhere, though I'd like to know at what outlet this was measured (presume 2nd floor bath taps?). If you run hot and cold concurrently is the flow much higher? You need to measure the flow rates (including dynamic flow) at the garden tap / kitchen tap to rule out internal plumbing restrictions, which you can re-plumb in 22mm if necessary.

Most unvented systems require a minimum cold water flow of 20L/min and 1.5 bar pressure; this in itself will deliver an average shower, let alone if the water has to overcome 2 floors' worth of gravity and especially if you ever intend on operating two showers at once. You need to check the dynamic / working pressure of the system, i.e. measure the pressure at the garden tap with all other outlets running concurrently, because this will determine if it's the house's pipework that's limiting the flow or the pressure of the main. The former can be rectified, the latter not so much (unless you opt for an accumulator).

So assuming 10L/min is the maximum flow supplied to your property from the cold main, which is fairly puny, you will almost certainly have one or both of a small incoming main that needs to be upgraded, or low static pressure, which can't be upgraded.

If I were you, my next steps would be to determine the incoming main's static and dynamic pressure and the size of the pipe supplying the property. From there you can determine whether a megaflo / other unvented cylinder is a viable option, or if you instead need to opt for large volumes of stored water with a pump to the shower.

On the face of it I'd be looking at large stored volumes of hot and cold water - a 20 minute shower at 20L/min is 400L (blended hot and cold of course) - with a 2-3 bar shower pump.

Given that the current boiler isn't a combi though, and the hot water cylinder is on the ground floor, how is the hot water to the current bathroom currently provided as you state there's no pump in situ? There's no gravity head for the hot in the bathroom on the 2nd floor so are you sure the current system is vented?

P.S. - absolutely nothing wrong with a 20 minute shower. This isn't 1940; people want their luxury showering experiences and I don't see why this is sniffed at.

 

[hornetstinger]

I don't take 20 minute showers. 5-10 minutes.

 

[Participant]

I don't take 20 minute showers. 5-10 minutes.

Will you be living in the OP's house? If not, shut up and go away perhaps?

 

[rexehuk]

Your options can't be determined from the information provided.

On the face of it, 10L/min flow is absolutely insufficient for an unvented system and would deliver a shower akin to an electric shower, let alone if someone flushes a toilet or runs a tap elsewhere, though I'd like to know at what outlet this was measured (presume 2nd floor bath taps?). If you run hot and cold concurrently is the flow much higher? You need to measure the flow rates (including dynamic flow) at the garden tap / kitchen tap to rule out internal plumbing restrictions, which you can re-plumb in 22mm if necessary.

Given that the current boiler isn't a combi though, and the hot water cylinder is on the ground floor, how is the hot water to the current bathroom currently provided as you state there's no pump in situ? There's no gravity head for the hot in the bathroom on the 2nd floor so are you sure the current system is vented?

P.S. - absolutely nothing wrong with a 20 minute shower. This isn't 1940; people want their luxury showering experiences and I don't see why this is sniffed at.

Cheers for the reply!

Measured next to boiler/tank (we have a sink down there) and that's above 20L minute which I guess is good? Don't think I even had the tap on full whack.

On the hot water front... have wondered that myself. All we have off the tank is a grundfos pump, but pretty sure that's for the central heating? It's a UPS2 15-50/60. I assumed it was the header pressure from the drop pushing it out...

On the 20 minute shower front... well I like my showers as does partner and we don't have baths so. If I'm dropping that much money on a wet room with a roof light above my shower, then you bet I'm going to enjoy it.

 

[rexehuk]

This is our cylinder by the way

http://www.screwfix.com/p/rm-indire...mm/47140#product_additional_details_container

 

[Participant]

There must be another hot water cylinder in the loft. The grundfos is a central heating pump and the cylinder is a standard indirect ie vented. Either that or there's another water pump you can't see or hear delivering 10L/min to your 2nd floor!

Either way, you need to measure the pressure to determine if unvented will be suitable.

 

[rexehuk]

There must be another hot water cylinder in the loft. The grundfos is a central heating pump and the cylinder is a standard indirect ie vented. Either that or there's another water pump you can't see or hear delivering 10L/min to your 2nd floor!

Interesting theory. I will check again in the loft but 99% sure it's just the exp and header in there.

Thing is we required the house, so all the old circuits are toast. If they put a pump somewhere it would be dead by now, unless it's hidden downstream of the boiler circuit I've revived.

Think I'll get a plumber over to work out what's going on!

 

[robj20]

There must be another hot water cylinder in the loft. The grundfos is a central heating pump and the cylinder is a standard indirect ie vented. Either that or there's another water pump you can't see or hear delivering 10L/min to your 2nd floor!

Either way, you need to measure the pressure to determine if unvented will be suitable.

Why must there be a cylinder in the loft, the header tank provides the pressure for the 2nd floor, got to be at least 2 meters differential between the taps and the header tank.

 

[Participant]

Why must there be a cylinder in the loft, the header tank provides the pressure for the 2nd floor, got to be at least 2 meters differential between the taps and the header tank.

Header tank supplies and accommodates expansion of the heating system, it doesn't provide pressure for the dhw system . Does it!?

In any case, the choices are negative head pump near the hot water cylinder or unvented system if sufficient flow and pressure is present.

 

[robj20]

Header tank supplies and accommodates expansion of the heating system, it doesn't provide pressure for the dhw system .

It does, you can either have one header tank or two. Two, one is for the expansion of the heating, the other is for the DHW. Ours had one which served as both.

 

[rexehuk]

It does, you can either have one header tank or two. Two, one is for the expansion of the heating, the other is for the DHW. Ours had one which served as both.

Well yeah we have that configuration. 1 large header tank, and 1 small expansion tank.

I've bought a pressure gauge (thanks Prime) so should know shortly what my mains pressure is coming into the house. Luckily there's a tap fitted right above my stopcock, so we'll see what it's kicking out.

 

[robj20]

Static pressure isn't much use by its self, you want the dynamic pressure.
Measure the flow of a tap, leave it running and also measure the pressure. So you have something like 3 bar at 10lpm. Along with static pressure it helps to show how your incoming is able to cope with flow.

 

[rexehuk]

Static pressure isn't much use by its self, you want the dynamic pressure.
Measure the flow of a tap, leave it running and also measure the pressure. So you have something like 3 bar at 10lpm. Along with static pressure it helps to show how your incoming is able to cope with flow.

I'll give that a go tomorrow.

The good news (I guess?) is that outside on the tap I'm getting close to 3 bar pressure... so does that open up options of other systems being viable?

 

[Participant]

Just less than 3 bar static is OK for an unvented system (the PRVs reduce anything incoming down to 3 bar anyway), but as robj20 says it's the dynamic pressure and flow that will matter most.

If your incoming main won't provide sufficient flow then your showers will have an initial burst at 3 bar followed by a rapid reduction as the downstream pressure reduces.

 

[rexehuk]

Had a plumber over today. Suggested we have two options, pressurised or moving to combi.

After seeing our flue which is about 5m in length he said best option is going for pressurised cylinder, as a replacement flue would add a fair cost.

Proposed he's going to run new feed from stop **** because they reduced down to 15mm for some reason. Said we have in excess of what's needed flow wise for the tank and decent pressure.

Just waiting for costs now, he seemed genuine and has good reviews on checkatrade. My only concern is him pressurising the heating, could blow some old joints as the work I've seen to date is flakey at best!

 

[samcat]

Are you thinking of installing Solar PV (electric) panels at some point?
If so a cylinder is a good idea, as you can have an immersion and a solar diverter that diverts electricity thats not being used and would be exported to the grid into the tank to make hot water for free.
Works well for us, I wouldn't be without a cylinder for this reason alone.

 

[mattyg]

Boiler room


You need to check your flow via an unrestricted outlet. Taps can vary massively. This is our system. Complete re pipe etc. 3 floors 17 rads.

You wont need two boilers (unless its a big house) We also have secondary H/W circulation. this pumps hot water past all the hot water taps so as soon as we turn the hot water we get a second of warm water before its hot. Even at the far end of the house. This, I believe is more efficient in a big house or even a busy house, than having to draw off cooled hot water to get new hot water.

I cant really tell any difference in temp on the hot from the closest to the furthest so probably not that much of a temp diff between outlet and return.

 

[rexehuk]

He checked our taps etc and confirmed all is good for the upgrade.

That is a serious install, are you running a swimming pool with the size of that pipework? Looks very sexy, copper is wonderful.