Comparing Boiler's Water Flow Rate

Katie_Bell

Hi,

I was wondering if anyone could help me? We've been looking in to Combi boilers and have got it down to two, but we're struggling to compare the water flow rate.

The first one is the Vaillant eco TEC plus 937 which states it has a flow rate of 15.2L/min at 65 degrees.

The second one is the Worcester Greenstar 420CDI Combi which states it has a flow rate of 17.2 litres per minute @ 35ºC temperature rise.

One describes a rate as a flat rate whereas the other describes it based on a temperature rise. I'm not sure how to compare the two. My other question is, is there any need for water to reach 65 degrees?

Many thanks,
Kate

gas4you

Usually no.

Legislation is coming in that will limit hot water to 48c. I beleive it is in place in Scotland already and in commercial premises now.

The 937 is a storage combi and will give 20 l/min for 10 mins.

Have you checked your cold mains pressure/flow?

If it is not at least these figures anyway, then you are wasting your money on such powerful combis.

The flow rate @35c rise is the standard you should be comparing.

Cardew

You are not comparing apples with apples here!

The Valliant has a built-in hot water storage tank which pre-heats water. It will only provide a smallish quantity of hot water at 65C and then it will be heating water in the same manner as any other Combi. Given mains water can be as low as 2C in the depth of winter there is no way any combi would heat water by 63C continuously.

Legislation is coming in that will limit hot water to 48c. I beleive it is in place in Scotland already and in commercial premises now.

How does that square with the legislation about 'Legionnaires disease' that IIRC stipulates 65C is required from time to time?? to prevent bacteria forming?

Pincher

I think there is a difference between stored water and free flowing water. The water coming out of the cylinder (or thermal store) might be 65+ degrees, but they go through a thermostatic mixer immediately so they don't scald you at the shower. Older systems don't have the mixer, but all the new ones seem to have them.

Katie_Bell

gas4you wrote: »

Have you checked your cold mains pressure/flow?

Thanks everyone, I do appreciate it. One other question, how do you check your mains pressure? Thanks

Canucklehead

Katie_Bell wrote: »

Thanks everyone, I do appreciate it. One other question, how do you check your mains pressure? Thanks

Good evening: use this to measure mains water pressure and a weir gauge for flow rate (or a bucket and a stopwatch;)).

HTH

Canucklehead

Owain_Moneysaver

Vaillant Ecotec 37kW

Worcester 42 CDI 30kW (this is for an LPG boiler??)

So the vaillant will be about 20% higher output.

You need to check the model numbers carefully.