New boiler £££ - is it actually worth it?

kittennose

Thanks. Yes will get some quotes. Boxt have put prices up over £1k compared to September when we first started looking...

mksysb

I wouldn't get a combi.  When it breaks down you will have no hot water.  With a tank, you have an immersion heater as a backup to use in an emergency.

MuckChucker

pensionpawn said:

kittennose said:

We have a 1989 boiler (Glow Worm Space Saver MKII) - gravity fed system.

I am lead to believe this is about 65% efficient.

We used 20,000 kWh of gas last year - which I calculate will cost us around £2,200 this year.

Our usage seems high compared to national averages - we are a family of 4 in a 4 bed detached but I am assuming this is all down to boiler efficiency, or lack of!

If we changed our boiler our energy consumption should be more like 16,00kWh with a new boiler? this is 20% less.

Calculation - 95% efficiency, less 10% lost during installation = 85% efficiency. A 20% improvement)

This would save us 20% only - which is less than £500 a year. 

Are these calculations about right?

Also I understand radiators are more efficient now, but I assume this is simply in terms of time to heat-up. Not energy efficiency to warm the actual house?

There are some other benefits in a new boiler, possible increase in water pressure (lord do we need it for showers!) and some space saving in the loft and airing cupboard, but don't really want to chuck money at something unessecerily.

I've just replaced my 1996 boiler which I believe was around 50% efficient. Yours will be less. My new Viessmann bolier is 94% efficient and should almost half my gas usage, which in your case would be 10,000 kWhrs at around 10.5p / kWhrs = £1050 pa which repays in 3.5 years. It's a no brainer.

Similar to quoted. We pulled out some stone age (easy 25+ yr old) boiler back in Feb, I think the house was built around it. We got a Veissmann heat only, new cylinder and had it all moved up out of the kitchen, not a cheap job but was needed and we're very happy with the results.

Comparison below - now if only the price hadn't shot up, we'd have been paying hardly anything all summer.

BUFF

Eldi_Dos said:

BUFF said:

The next replacement cycle will almost certainly require stored DHW i.e. putting back what was taken out for a combi. How long do you plan to stay in this building?

I wonder if you could explain your thoughts on this.I am in similar position as Op  and would appreciate hearing more about this aspect.

The next replacement cycle (10, 15 years or whatever) based on current thinking will almost certainly involve a heat pump.
Heat pumps can't do the rapid temperature gain that a combi can (they favour low & slow) so you will either heat a hot water tank via heat pump or use an electric shower at 3x the price of using hot water from the heat pump.

Dolor said:

A boiler will not condense until the boiler flow temperature is below 56C: the lower the flow temperate, the higher the boiler efficiency.

I think that you mean return temperature needs to be below 56C (as in your later post) not flow temperature.:

Finally, for maximum efficiency choose a boiler that has Opentherm control. Suffice to say that it is akin to driving through London with all the traffic lights on green. Opentherm is now mandated in many European countries which is why I chose an Atag boiler for my previous home.

Can I tweak that & add "or similar"? In fact iirc there is some evidence that Vaillant/Viessmann/Bosch's similar but proprietary solutions are marginally better (but we really are talking by a gnat's unmentionables). Opentherm is just a communications protocol between the boiler &  the controls afterall. 

Miser1964

>possible increase in water pressure (lord do we need it for showers!) <

Showers in the plural means a basic combi probably won't give you what you want. You'd be better installing a system boiler configured to what the trade call Priority Domestic Hot Water (PDHW) with an unvented 250l cylinder. This'll let you run two or more showers at the same time with good pressure and decently hot water for everyone.

Boilers now have many optimisations such as weather compensation and OpenTherm control of central heating to make them as efficient as possible. It's generally better to get the manufacturers own controller/room-stat rather than go third party such as Nest or Hive. 

As others have said, to get the full 10/12-year manufacturers guarantee for a new boiler you'll need to budget for a power flush after running a vented system.

A competent installer will calculate the heat loss from the property to determine the kWh rating of the boiler needed to heat the property when it's -2°C outside. They'll also need to calculate if the existing radiators can heat the property with the C/H water flow temp set to 55°C and drop the return temp low enough (aka Delta T) so the boiler condenses.

These days installers need to be as good with a computer as a blowlamp! 

sandy700

I replaced my warm air heating with a combi and my usage dropped from 22,000/24,000 kWh a year to 14,000/16,000 kWh a year of gas.

I then increased the insulation in the loft, got cavity wall insulation and replacement double glazed windows and last year my usage was 12,000 kWh.

So from 24,000 kWh max to 12,000 kWh a year over 31 years for the sum of £17,000 in the past 6 years

I won't see a profit in my lifetime but the house feels a lot more comfortable.
A 3 bed semi.

[Deleted User]

BUFF said:

Eldi_Dos said:

BUFF said:

The next replacement cycle will almost certainly require stored DHW i.e. putting back what was taken out for a combi. How long do you plan to stay in this building?

I wonder if you could explain your thoughts on this.I am in similar position as Op  and would appreciate hearing more about this aspect.

The next replacement cycle (10, 15 years or whatever) based on current thinking will almost certainly involve a heat pump.
Heat pumps can't do the rapid temperature gain that a combi can (they favour low & slow) so you will either heat a hot water tank via heat pump or use an electric shower at 3x the price of using hot water from the heat pump.

Dolor said:

A boiler will not condense until the boiler flow temperature is below 56C: the lower the flow temperate, the higher the boiler efficiency.

I think that you mean return temperature needs to be below 56C (as in your later post) not flow temperature.:

Finally, for maximum efficiency choose a boiler that has Opentherm control. Suffice to say that it is akin to driving through London with all the traffic lights on green. Opentherm is now mandated in many European countries which is why I chose an Atag boiler for my previous home.

Can I tweak that & add "or similar"? In fact iirc there is some evidence that Vaillant/Viessmann/Bosch's similar but proprietary solutions are marginally better (but we really are talking by a gnat's unmentionables). Opentherm is just a communications protocol between the boiler &  the controls afterall. 

Correct - I did mean return flow temperature.

Have you ever had a boiler with full Opentherm control? I have and it makes a big difference to the way that the boiler operates - for example, less boiler cycling.  I can do no better than quote from the Intergas website:

‘OpenTherm communications allow the transfer of heat demand information from the thermostat to the boiler enabling it to proportionally control the flame size and lower the flow temperature as the room approaches set point. This means there is minimal overshoot of set temperature and the room temperature is maintained at the comfort level more accurately. It also means the return temperature is kept low, which is of particular importance to the efficiency of condensing boilers. It is a way to achieve ‘load compensation’ as defined by Building Regulations and is an open standard that multiple controls and boiler manufacturers have successfully used for decades.

It can help the boiler to modulate and run more efficiently in condensing mode for longer periods.’

BUFF

Opentherm is just a communications protocol between the controls/sensors & the boiler's inbuilt modulation controls. It's the algorithms in the boilers & the offboard controls etc. that are responsible for the improvements in efficiency not the communications protocol itself.
The Opentherm spec. was sold by Honeywell (a 3rd party controls supplier) in 1996  for £1 to the newly created Opentherm Association - essentially the 3rd party suppliers didn't want to be locked out of the market by boiler manufacturers & lobbied for an open market & to be able to continue to supply.

Vaillant, Veissmann & Bosch Group (& no doubt others) all have equivalent but proprietary communications protocols. There is some evidence that these products actually perform marginally better than Opentherm (as you rightly say in NL boilers have to by law be able to use Opentherm so if a boiler manufacturer with a proprietary solution wants to sell there they have to offer an adapter to translate) - the manufacturers certainly would say so.
Some manufacturers (e.g. Baxi) have used wiggle room in the Opentherm spec. to populate device IDs such that their Opentherm boilers wouldn't actually talk to other manufacturers' Opentherm controls. Ideal have an Opentherm thermostat, Halo, that they say won't work on other manufacturer's boilers ...