Unvented vs 38KW worcester 38kw

[jay2k]

I had 4-5 guys come in with all having different proposals.

Pressure is 3 bar, flow rate using a crude bucket is about 25 liters in 20-30 seconds.

I just need to have two showers working at 7:30am without fuss.

Option 1: Re-use 10 year old Main HE 24KW condension system boiler with new Megaflo (or similar)

Option 2: use single 38KW Worcester Greenstar combi boiler. Will I need 42KW?

38KW is £1400 and flow rate of 16.4 Ltr while 42KW is £1600 with 17.1 flow rate. £200 for less than 1 liter per min seems much.

Glow-worm Energy 35 Store offers a claimed 20 ltr floor rate for circa £1400

thanks

 

[Darren Jackson]

I would opt for option 1, Keep existing boiler. But if you go for a combi be wary that in the event of a breakdown you have no hot water back up till it is repaired.

 

[ShaunCorbs]

Combi won't run two showers at once

If you want to run two showers at once

Heat only boiler and an unvented with an accumulator

 

[kris]

Option 3 Get 250l unvented cylinder 25lpm for 500 quid and a new system boiler ideal vogue 18 or 24kw 900 quid (10 year warranty) plus cylinder 25

 

[cr0ft]

As already mentioned, a combi boiler won't run 2 mixer showers well in the middle of Winter. If the existing boiler works fine then spend the money on an unvented cylinder.

Also, it's very important to measure water mains dynamic pressure as well. 3 bars of pressure is great as is approx. 50 litres per minute, however if the 3 bars is coming down a lead pipe with a tiny internal diameter, pressure will drop off very quickly when two taps are open at the same time. This will manifest itself with 2 poor performing showers when the unvented cylinder is installed. It's definitely worth having this properly tested before taking the plunge installing one!

 

[Harvest Fields]

Definitely not a combi. Like the above have said a combi will not power a bath and a shower or 2 showers at the same time. It frustrates me that engineers are still quoting for combi's in large houses or houses with a high hot water demand. These are the engineers that never go back to boilers that they fit once they break. But hay ho. It keeps me busy I suppose.