Central Heating - Combi boiler vs cylinder/header tank

tdenson

I am just about to have central heating fitted to a bunglaow I just inherited from my mother. Should I go Combi boiler or the more traditional system, the two firms I have asked to quote have gone for different systems.
As it happens I also own a pair of semis (in which the extended family live with us) and one of them has a cylinder/header tank and the other a combi boiler, but even so, I'm not sure of the relative merits. One thing that might influence the decision is that as a second home it won't be occupied a lot.

no1catman

Combi every time.

Recently moved from a terraced house, which had a conventional system. I was all too often, going into the loft changing the washer on the cold tank.
I changed that to a combi, took up less space in the kitchen than the old boiler, no hot water tank upstairs - freeing up more storage space. Bills went down, when you want hot water, it soon comes - you don't have to heat up the hot water tank first.
Then when I moved - to a semi, changed boiler - well it was over the cooker (against regulations) to this time a condenser combi - only thing we do is top up water pressure occaisionally. Otherwise great - very surprised you'd be offered the old style system now.
The only downside, is having a hot water tank - gives somewhere warm to dry off washing - when rads aren't on.

macman

Both have their merits. Depends who is gong to live in the property and lifestyle, number of bathrooms?
You need to pin down a spec before you get quotes, as otherwise you are comparing 2 completely different things.

bengasman

The system with a header tank is hopelessly outdated, uneconomical and unhygienic. The only reason I can see to use them is if the water supply is way below the standard.
The modern version with an unvented cylinder is much better, but a lot more expensive.
Provided the water supply is ok, an properly installed combi will do fine for 90%+ of households.

Moneysava_wannaB

bengasman wrote: »

The system with a header tank is hopelessly outdated, uneconomical and unhygienic. The only reason I can see to use them is if the water supply is way below the standard.
The modern version with an unvented cylinder is much better, but a lot more expensive.
Provided the water supply is ok, an properly installed combi will do fine for 90%+ of households.

agreed. can't see why anyone would want to install a none combi system, no tanks in loft, no waste of space hot water cupboard, no low pressure showers(mains pressure with combi), no having to wait for the whole hot water tank to heatup to have bath/shower also wasting excess hot water.

macman

You don't get mains pressure showers with a combi, you get the maximum hot flow that the combi can supply. That's the usual downside with them.

Cardew

Just to show there are two sides to any discussion, I have both systems currently - a combi in an annex - and have used both systems in other houses. For me the conventional system wins hands down.

As Macman states in post #3 there is merit in both systems. In general I suggest that smaller properties are more suited to combis where the advantages in space saving are more important.

However the biggest drawback is a combi's ability to deliver a sufficient flow of hot water - particularly in winter and particularly if hot water is required at two points in the house.

Modern well insulated hot water tanks lose surprisingly little heat - and for most of the year that heat is not 'lost' as it warms the fabric of the house, and a tank in an airing cupboard is a must as far as my wife is concerned.

Also with a combi, depending on its location, there can be quite a loss of water in the pipes - a typical installation will have the Combi downstairs and the bath/showers upstairs. To overcome the problem of a delay in hot water reaching the taps, when a combi first fires up, the more advanced combis have a internal reservoir - a mini hot water tank.

Certainly not a 'one horse race' IMO.

gas4you

Personally I would go for either a good quality combi, or an unvented cylinder option, along with a system boiler.

This will give a 'dry' loft and all the advantages of your available mains pressure and flow.

For the unvented you will need at least 20 l/m and 3.5 bar pressure to make it worthwhile.

As bg has said, tanks in the loft is very archaic now and should be avoided where possible on new installations.

Mains pressure and mains flow are completely different things and don't really relate to each other.

macman

With an unvented set up, does it matter where the cylinder is in relation to the shower/bath outlet and the boiler, since gravity is of less importance?
So, for example, could you have a ground floor boiler and cylinder, and would that power a 1st floor shower, assuming that the mains pressure is sufficient?
Or is is still advisable to have the cylinder at the same height (or higher) than the outlet points?

gas4you

As long as the safety discharge pipe from the unvented cylinder can always 'fall' away from the cylinder to its termination point, you can put the unvented cylinder on the ground floor, even a basement, if it has a drain built in the basement.

It will not affect its performance.

WhiteHorse

Combi, without a doubt. Careful selection of capacity and thoughtful siting should resolve any issue related to demand and wastage.

I sited my new combi underneath the bathroom (maximum run for hot water about three feet), and next to the kitchen sink (run about three feet as well). I selected a larger capacity unit because I want to run a shower from it as well and don't want any problems when running a sink and the shower at the same time.

Compare this to a friends house, where the run from boiler to bathroom is seventy feet.