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New Heat Pump - mixer shower pressure

Air Source Heat Pumps (ASHPs)

Last Post by Spanners 1 year ago

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Spanners

(@spanners)

New Member Member

Joined: 1 year ago

Posts: 3

Topic starter 27/03/2025 2:52 pm [#2225]

In just over 2 weeks I will have a Daikin heat pump, hat water cylinder etc installed. I have an electric shower which I want to replace with a hot and cold mixing shower at a later stage after the heat pump installation.

When I had my heat pump survey the guy said that my water mains pressure was 7.5 Bar which I thought was pretty high, when looking at the specs for the mixer shower I am intending to install, it states that the water pressure to the shower is recommend to be between 2.5 and 3.4 Bar.

My Daikin hot water tank will be on the ground floor and my mixer shower will be on the first floor.

My question is that after the heat pump has been installed, will my domestic hot and cold water still be at 7.5 Bar and if so, what would be the best way the reduce the pressure (and maybe equalise the pressures between the hot and cold water if needed) and also where would be the best place be to install any water pressure reducing or equalising valves that are needed?

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shower water pressure

JamesPa

(@jamespa)

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27/03/2025 6:24 pm

Posted by: @spanners

↑

My question is that after the heat pump has been installed, will my domestic hot and cold water still be at 7.5 Bar and if so, what would be the best way the reduce the pressure (and maybe equalise the pressures between the hot and cold water if needed) and also where would be the best place be to install any water pressure reducing or equalising valves that are needed?

The new installation will come with a pressure limiter which will limit the water pressure on all hot outlets and any cold outlets which were previously 'indirect' (ie fed from a tank in the loft) to 3 bar. This works just great for a shower.

Alternatively it is possible to install a pressure limiter on the incoming mains.

Hope that helps.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Mars

(@editor)

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27/03/2025 10:26 pm

Posted by: @spanners

↑

When I had my heat pump survey the guy said that my water mains pressure was 7.5 Bar which I thought was pretty high, when looking at the specs for the mixer shower I am intending to install, it states that the water pressure to the shower is recommend to be between 2.5 and 3.4 Bar.

7.5 bar… Bloody hell. That’s not mains pressure, that’s a fire hose 😂

You could probably jet-wash your driveway with that.

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Spanners

(@spanners)

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Posts: 3

Topic starter 27/03/2025 10:36 pm

@Mars I know, unless the surveyor guy was mistaken? I might just double check it with a gauge to be sure.

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😂

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JamesPa

(@jamespa)

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28/03/2025 7:51 am

Posted by: @spanners

↑

@Mars I know, unless the surveyor guy was mistaken? I might just double check it with a gauge to be sure.

He may well be right. I have 9 bar which, on one occasion, burst open a steel radiator (with a bit of help from my stupidity).

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Judith

(@judith)

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29/03/2025 9:04 am

Mixer showers need virtually identical hot and cold pressures (or at least our new one did) or you need a high flow to mix properly. Our mains varies from 1.5bar (very poor, they suffer at the top of the hill) to 4 normally. Our retrospectively fitted pressure reducing valve is on the output of the water softener, usually set about 2 bar.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

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JamesPa

(@jamespa)

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30/03/2025 9:24 am

Posted by: @judith

↑

Mixer showers need virtually identical hot and cold pressures (or at least our new one did) or you need a high flow to mix properly. Our mains varies from 1.5bar (very poor, they suffer at the top of the hill) to 4 normally. Our retrospectively fitted pressure reducing valve is on the output of the water softener, usually set about 2 bar.

Agree. Fortunately UVC installations (which almost always are included with an ASHP) include a pressure reducing/balancing valve to supply cold water to the former 'indirect' circuit (if there was one) at the same pressure as the hot water from the tank thus sorting this out, assuming your plumber knows what he is doing! Both hot and cold for the mixing shower need to be supplied from this valve. Many times your plumbing will be such that this is automatically the case, but this isn't guaranteed unless checked because plumbing can be weird and wonderful if 'added to' at various times. This sort of thing is part of a competent ASHP install.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Transparent

(@transparent)

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30/03/2025 11:10 am

Posted by: @spanners

↑

My Daikin hot water tank will be on the ground floor and my mixer shower will be on the first floor.

Just note that this will yield a reduction in pressure of about one-third Bar between the DHW tank and the shower.

1 Bar is about 10 metres head of water.

Each floor in a house is approximately 2.6m, including the joists.

And the measurement is to the shower-head, which is about 2m above FFL (Finished Floor Level).

The HP installer will almost certainly fit a pressure-reducing valve on the cold incomer to the property.
Otherwise he has greater risk that the high water pressure will cause leaks in the new pipework he fits for domestic H & C feeds.

It won't affect the circulating water that goes through the heat-pump and radiators because that's a closed system.
It's pressurised to about 1½ Bar through the filling-loop when it's installed.

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Spanners

(@spanners)

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Joined: 1 year ago

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Topic starter 02/04/2025 11:36 am

Just a little update, I eventually decided to put a pressure regulator in just after the main stop tap under the sink to bring the pressure down from the 7.5 Bar to a more reasonable 3 Bar, if it needs to be adjusted later, I can always tweak it a little.

My Heat Pump install will go ahead in 12 days and I will mention what I have done here as there will be a discrepancy in what was stated on the Heat Pump survey. I’m not sure if the installers would have done the same thing to reduce the pressure but thought I’d do it anyway just to make sure in preparation for a mixer shower that I will be installing later in the year that would need a pressure to be less than 3.4 Bar as stated in the manual.

Thanks to everyone who replied to my original post. Keep up the good work peoples👍