New combi

[james2006]

Hi - I am looking to replace my boiler. Initially I was advised the water flow rate coming into the house was too low for a combi (only had around 12l/min).

However, I found out today that the stop cock was not fully open. With the stop cock open I get 21l/minute.

I am a little confused on measuring pressure as I have had comflicting views from plumbers. I have taken 2 measurements:

1) Standing pressure - this measured 3-4 bar and was measured at the outdoor tap.

2) Working pressure - this measures 1.5-2 bar and was measured on the outdoor tap with another mains fed tap running at the same time.

The house has a 2 x showers.

With these measurements would a combi work ok delivering 2 acceptable showers? I was thinking about a worcester 42 CDI? If not the alternative is to stick with the gravity feed system and add shower pumps.

Appreciate any thoughts.

Cheers


James

 

[DP]

Take it you have two showers and other hot water draw off? If yes, you will need quite a regimented regime at home for system to work. The boiler will only supply a specific flow rate of hot water. As other draw off are opened, delivery of hot water is divided. This division may not be propostional but will depend on height from the boiler to the delviery point as well as the distance from boiler. For example, if the boiler is on ground floor, one shower on ground floor and other upper level and you are in the shower upstairs and some one runs the (groundfloor) kitchen tap, your shower might not get required amount of hot water.

Then take into consideration the gas line to the boiler from the meter. 42kw will be like a V16 Bentley. Boiler will be looking to burn a hole in your pocket when pedal is to the metal but when all hot taps are running, performance may not be Bentleyish

 

[kevindgas]

21litres a minute divided by 2 = 10.5 litres per shower, not a fantastic flowrate for a shower, but may be ok. doubt it would support a rainwater type head though.

 

[james2006]

Thanks - So the concern is the mains not delivering enough water flow? Eg the mains will be divided accross hot and cold and then accross 2 showers.

What would be your recomendation re a new boiler

 

[james2006]

what is a reasonable shower flow rate? Any one know what a reasonable electriv one is out of interest?

at the momenet my gravity feed shower is 4l/min.

 

[muggles]

If your current shower is 4l/min then I would suspect you'll find running off a combi a great improvement, in which case go for it. I'd recommend an Intergas Combi Compact HRE 36/30, same flow rate as the Worcester but a much better boiler

 

[dcawkwell]

250litre Unvented cylinder and system boiler needed.

Combi boiler isn't suitable to drive up to 2 showers.

 

[holty]

why combi? unvented springs to mind. boiler packs up you have immersion back up. good relaible system or heat only and robo kit. will be more reliable than a combi. better flow rates. the list goes on.

 

[james2006]

Would like to fit an unvented but cost is the issue. Quotes for a combi are around £3k whilist an unvented system is upwards of $5k - does that sound correct??

 

[holty]

not really think the $5000 is equivalent to £3000. depending on the exchange rate and US or OZ. seriously though without looking at the job budget etc its hard to give an idea of whats best for you.

 

[kevindgas]

Would like to fit an unvented but cost is the issue. Quotes for a combi are around £3k whilist an unvented system is upwards of $5k - does that sound correct??

nice work if you can get it!! would have thought you could do a lot better on an unvented system

 

[bengasman]

If you are happy with two working showers without the need for Niagara Falls, a 42 cdi would do the job nicely. Properly installed unvented system will perform better, but will indeed cost several thousand more.

 

[james2006]

Thanks

 

[bengasman]

Forgot to mention: Viessmann 100W-35 kW is a bit less powerful, but will still do two showers, is a better boiler, and a lot less expensive.

 

[holty]

just realised on a recent post i advised on a rinnai twinflow. i'v fitted the rinnai water heaters on camp sites and mostly more seen on a commercial basis. this version is twined with an atag boiler. which iv not fitted but regarded as the best on the market by some. good boiler coupled with a high flow water heater.