Combi vs Conventional Boiler???

Jit7

Hi
The house that we're buying has a old one-way heating system. We've been advised to get a new system put in but not sure whether to replace with conventional boiler or go for a Combi system. Its a 3 bed semi and it'll just be me and my husband living there.

Really not sure which one to go for - combi or conventional???

Please help!

thechippy

The main disadvantage of combi's is that some of them would struggle to run two hot supplies at the same time, so for example, are not perhaps suitable for a house with two bathrooms.
The advantages are, you would lose the two tanks in the loft, along with the cylinder in the airing cupboard and associated plumbing. Also, as the hot water is on demand, you never run out, so it's easy to run two baths in a row - not so easy from a cylinder as the water would have to re-heat.

We went from an indirect system to combi and never looked back. Our loft is now huge without the tanks and we regained loads of space for storage in the airing cupboard. It's normally a cheaper installation as well.

Our monthly direct debit for gas halved after the new system was installed.

Farway

I'm with thechippy on this one, when I changed from old floor standing boiler to a combi mu gas use dropped over 40% just by not having to heat a tank of water every morning

Works fine for me, but only me using it

Cardew

Farway wrote: »

I'm with thechippy on this one, when I changed from old floor standing boiler to a combi mu gas use dropped over 40% just by not having to heat a tank of water every morning

Works fine for me, but only me using it

That statement is simply unsupportable.

I cannot see how you can possibly deduce the amount of savings attributable to '"just not having to heat a tank of hot water every morning"

By far the biggest gain will be the efficiency of any type of new boiler(combi or freestanding) over the old boiler.

A well lagged tank full of hot water at 65C will lose heat that in 24 hours will take about 2kWh to replace. That is when there is no water used.(tanks are tested to a BSI standard)

In practice when you have hot water on timed the water will not be at 65C 24/7 so the heat losses will be less than 2 kWh a day. So 500kWh a year might be an average loss(£15 or so a year)

In any case that heat is not 'lost' as it heats the fabric of the house.

Depending on the siting of the boiler and HW tank, the longer feed to the bathroom taps from a combi can result in additional losses.

Many combis now have their own internal HW reservoir(with its own losses) to enable 'instant' hot water.

It is also my understanding that it is more expensive to fit a combi to an existing 'conventional' system as the removal of tanks and additional plumbing is a considerable cost.

I have both systems and for me the conventional HW tank system wins hands down.

thechippy

My old system was gravity, so would have been necessary to convert it to fully pumped, which is more labour and materials than going over to a combi.

Removing the old tanks and exposed pipework takes hardly any time at all. You can do it yourself if you want. The small tank will come straight out of the loft hatch and you can cut down the main tank with a handsaw.

bambibashercol

A combi is not always suitable as the incomming mains need to be checked. If you are on a shared mains then forget fitting a combi.
A lot of problems with combi boilers is they can be undersized. The installer fitting the wrong sized boiler to save money or make there quotes look good.
Gas supply to the boiler may also need upgrading as a large combi needs a large gas supply.
Your installer should ask you what your hot water needs are, if you mainly take showers then a correctly sized combi will be fine for most needs.

kennyg123

I had an extension about 7 years ago and had a combi fitted. Really was the worst thing I ever did as the thing is so temperamental! When the heating is off, its pot luck as to whether I get hot water or not. My plumber has given up with the boiler and suggests I have a conventional one put in instead. Of course, the tank has now gone, as well as the airing cupboard. We've struggled on as can't afford to change yet!

Gerrard_8_lfc

My general view is that non combi's are less problematic than combi's

combis seen more prone to breakdown.

bockster

we had combi about 18m ago and i'm thrilled with it, especially from a financial point of view. its 37kw vaillant, 4bed detatched, 2 adults, 2 kids.
our annual gas usage was in the region of 16600kwh's, (admittedly when energy was cheaper and i was a little less focussed on money saving).

usage this last year was 6600kwh's, at, lets say 3.8p/kwh, thats a saving of £380 p/a. this is being, lets say, quite thrifty with the hot water, indeed in summer the boiler is turned off most of the time and goes on when bath required or dishes need hand washing. (this avoids all the short on/off cycles that usually result in no hot water actually reaching the tap, a lot of combi users will understand what i mean).

i disagree somewhat with the statement that heat loosses from hot water tanks are not so much lost as heat the fabric of the house, although all homes are different. warming the fabric of the house is only useful for the winter months, and even in winter most hot water tanks are upstairs and lost heat will try to escape directly upwards, my old installation as an example, through a pooly isulated section of the loft, what with all the pipes to the tanks and no insulation below the tanks which are invariably in the visinity.

a financial bonus we don't always think of is that theres no pilot light on a combi. i've seen recent posts on here where people suspect the pilot light alone could be costing them about £90pa! perhaps a worst case, but...

so, for me at least, the way a combi works can save you more money perhaps than the energy efficiency of the boiler. our old boiler was approx 73% efficient, new one is 92%ish, as you can see my total reduction in gas usage is much higher than this 19% boiler efficiency gain.

as for running more than one shower, say. our current electric shower is on low power and runs at about 1 l/m, the combi is filling the bath at about 14 l/m even now its colder. i think when i install 2 new showers off the combi it will cope easily.

we also gained an unobstructed loft, an airing cupboard for storage and fitted the combi in the loft freeing space for new kitchen (initial reason for new boiler)

this has been my experiance,
hope it helps,
bockster

thechippy

bambibashercol wrote: »

A combi is not always suitable as the incomming mains need to be checked. If you are on a shared mains then forget fitting a combi.
A lot of problems with combi boilers is they can be undersized. The installer fitting the wrong sized boiler to save money or make there quotes look good.
Gas supply to the boiler may also need upgrading as a large combi needs a large gas supply.
Your installer should ask you what your hot water needs are, if you mainly take showers then a correctly sized combi will be fine for most needs.

Being on shared mains is not always a problem, as long as the incoming pressure is suitable.

An engineer fitting an undersized boiler does not mean a combi is unsuitable. It means the wrong size was fitted.....:rolleyes:

If it is not a 2 bathroom home, a combi is fine!

These days, combi's are no more unreliable than a condensing system boiler.

Most boilers now need a 22mm gas supply, so it's common to have the gas supply uprated when having a boiler change.

olly300

thechippy wrote: »

Being on shared mains is not always a problem, as long as the incoming pressure is suitable.

Agreed.

I'm on shared mains and have a combi boiler no problems.