System boiler and UVC set up

30 Mar 2008
Reaction score
Harrow, London
United Kingdom
Figured i should start a new thread as my questions no longer relate to the Vaillant 938 combi.

I don't have a large DHW requirement (as there will only be me and, possibly, one other adult in the house for now), but it is a four-bed two bathroom property with rads on upper two floors and UFH on GF.

@Phill Peck has suggested a Viesmann 100/200 and 90-150L UVC (Viesmann or Gledhil) on a four-pipe system.
@Dan Robinson is suggesting an Intergas (not sure which one) on a three-pipe config. No idea how a three-pipe system works, tho!

I'm trying to keep costs down, so what would be the best set up? The Gledhill and Telford cylinders look the best bang for the buck, but not sure on the boiler.
Sponsored Links
The hot water requirements depend on the number of people living there.

BUT consideration has to be given to the size of the property and the number of people who could live there.

A four bed property could easily house eight people.

A rule of thumb for storage volume is 50 li plus 50 li per person. So for two people a 150 li would be adequate.

But that would not be good for the eight people.

So if I was doing it then I would advise a 300 li cylinder as that would be better suited to the capacity of the property.

Contrary to some people's thinking, the cost of that is little more to install, only the difference in price of 300 li to 150 li cylinder and perhaps £150 to £200. Installation cost is the same.

Once fitted and in use, there is no increase in operating costs as the standing losses are very small and little difference between 150 li and 300 li cylinders.

Funny how my 4 bed property works perfectly well on a 170 litre Joule on an Intergas Eco RF 24.

Previously I had a 150 litre cylinder.

Tony you don't half talk nonsense half the time. It's starting to get tiresome.
I have 5 bed houses with multiple bathrooms often with 6 people in occupation, happily sitting on a 250 cylinder and Eco RF 30's and RF36.
Sponsored Links
Intergas boiler (ECO RF for preference - ten year warranty) set up to hot water priority as per Dan's suggestion, with a Joule Cyclone cylinder
A rule of thumb for storage volume is 50 li plus 50 li per person. So for two people a 150 li would be adequate.

You are wonderfully inconsistent moan like hell when people use BTUs but still size cylinders based on an outdated idea of them having a 3kW coil!
Properly sized a cylinder will supply the hot water demand without needing very much reheating in between. So the boiler can deal with heating requirements during cold weather.

That enables the boiler to be correctly sized for the property heat loss with only a 2 kW extra allowance for hot water heating in accordance with the EST advice on best practice.

Of course when Dan fits an oversized boiler then the smaller cylinder will suffice but only because it relies on the extra boiler capacity for reheating during hot water demand.
The Intergas Eco RF are combis, right? In which case, why a combi as opposed to a system boiler? And would the 24 be sufficient?
They can be used as system boilers. They have the 10 year warranty. The Intergas system boilers only have 7 years and don't have the remote management facility of the Eco RF range.
A combi boiler can also be used to heat a cylinder as well as deliver hot water from it's combi function.

Typically a combi can be used like that to give DHW for the kitchen and then the cylinder can give a higher flow rate for showers and baths.

Although called a "24", that Intergas model only gives about 22 kW to the DHW and 18 KW to the CH.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links