best hot water system for low pressure mains

[joe brown]

Hello everyone, I have been asked by a friend what the best solution is for them, they want a new system installed but have low pressure at the mains, obviously stored water is the answer but could it be powerfull enough to have an unvented system...any help appreciated

 

[dancinplumba]

hi if pressure not high enough for a combi then its not going to be high enough for unvented imo, you could put whole house pump in fed from cws tank and dhw cyl

 

[lame plumber]

accumalator for better flow rates, but bulky, system boiler will remove f & e tank fm roof space as well

 

[joe brown]

i was under the impression you could get away with an unvented system as it relies on the water pressure instead of gravity so the pressure didnt have to be as high... i assumed thats what they where for..thanks pal... i dont think they wanted to revert to old gravity systems.. are you sure they cant run on low pressure

 

[lame plumber]

unvented systems need pressure to work, upto 3 bar so no pressure no uv sys, gravity fed only option with roof tanks, supplemented with pumps and accumalators

 

[TBServices]

i was under the impression you could get away with an unvented system as it relies on the water pressure instead of gravity so the pressure didnt have to be as high... i assumed thats what they where for..thanks pal... i dont think they wanted to revert to old gravity systems.. are you sure they cant run on low pressure

Tbh if you don't know the requirements for unvented cylinders, you can't be qualified to install one, so I can't imagine you'd be pushing that route!

 

[joe brown]

i havent done my unvented your correct but i was under the impression they operate from 1.5b to 3.0b i may be wrong,

 

[lame plumber]

so what is the dynamic mains water pressure your looking at?

 

[dancinplumba]

i havent done my unvented your correct but i was under the impression they operate from 1.5b to 3.0b i may be wrong,

they have 3bar prv will work less than that but if you have 1.5 bar then stick combi in unless its got large dhw demand

 

[Nostrum]

You'll also need a good flow rate for unvented as every tap is relying on the same source. You'll need a massive incomer to achieve a good flow rate with poor pressure which I can't see them having.

Stored gravity sounds like the best option, but you need to measure, dynamic pressure and flow rate to assess the other options.

 

[Best]

Agree ^^^
Stored gravity may be best option & can have good flow rates if the cold tank is high enough & large pipes are used from it & also taps & shower valves used that are suitable for low pressure. Depending on the owners needs, but if they want very high flow, a pump can be fitted beside the hot cylinder for whole house or supply just a shower valve.

 

[Reg Man]

Pressure and volume together need to be sufficient. 2-3bar 20l per min preferably.

I came unstuck once on a isolated area. everything was fine for 2 years great pressure and volume, then someone built a huge housing estate in the field next door and they robbed alot of the pressure and flow.

 

[AWheating]

measure the dynamic pressure and flow rate of the cold main and then come back and tell us what it is.