Water Meter system boiler vs combi

Steveotwo

Considering upgrading to a combi but one thing that crossed my mind. which uses less water, in my last place we had a combi and luckily wasn't on a water meter as you had to run the tap for about 20 seconds until it got hot. Here with a system boiler it comes out hot more or less straight away. 

Would a combi cost me more in water?

vacheron

It more depends on how far the combi boiler (or hot water tank for a system boiler) is from the tap you are using. 

A system boiler will store the hot water elsewhere until you need it, if this is closer to your tap than the boiler (in pipework terms, not physical distance, then the hot water tap will heat up quicker. 

In our case, our boiler (system) is in the garage literally 6 feet from the tap in the kitchen, but the hot water tank is in the loft and takes a convoluted route to the kitchen tap due to the previous kitchen layout, so I have to run the kitchen tap for about 30-40 seconds before the water from the loft tank reaches the kitchen tap. If I replaced that with a combi and direct pipework it would be hot in a few seconds.

Albermarle

vacheron said:

It more depends on how far the combi boiler (or hot water tank for a system boiler) is from the tap you are using. 

A system boiler will store the hot water elsewhere until you need it, if this is closer to your tap than the boiler (in pipework terms, not physical distance, then the hot water tap will heat up quicker. 

In our case, our boiler (system) is in the garage literally 6 feet from the tap in the kitchen, but the hot water tank is in the loft and takes a convoluted route to the kitchen tap due to the previous kitchen layout, so I have to run the kitchen tap for about 30-40 seconds before the water from the loft tank reaches the kitchen tap. If I replaced that with a combi and direct pipework it would be hot in a few seconds.

As above, we have a system boiler and every hot water outlet in the house takes between 15 and 30 seconds to run hot, due to long pipe runs.
Although in terms of water usage I do not think it is really significant, unless you are turning them on many times a day, every day.

MattMattMattUK

The cost of that water is going to be tiny. Over those 20 seconds it probably gets through 4 litres, so around .9p per use, the cost of the heat loss from a modern hot water tank is likely higher than that. 

ThisIsWeird

Steveotwo said:

Considering upgrading to a combi but one thing that crossed my mind. which uses less water, in my last place we had a combi and luckily wasn't on a water meter as you had to run the tap for about 20 seconds until it got hot. Here with a system boiler it comes out hot more or less straight away. 

Would a combi cost me more in water?

Modern combis will have the option of 'pre-heat'. This will keep the boiler's heat-exchanger hot, ready to supply DHW at the turn of a tap. The only other delay in this case would be caused by the distance the HW has to travel to come out the tap, and that'll be the same with any standard domestic system.

However, I have turned my P-H off on my combi, because the damned thing was firing up every few minutes to keep the boiler hot, not only imo an utter waste of gas, but a far greater level of wear on the boiler parts.

A combi boiler, in any case, will be more prone to faults and breakdowns, compared to a system boiler. Using P-H will only add to that.

My GlowWorm is already pdq at heating the DHW from cold, so I really don't miss the P-H feature.

To answer your Q, I can only conclude that - yes - a combi will use up more water if you keep the P-H off, or more gas if you keep it on! But I doubt the actual amounts are all that significant, as most usage will be Central Heating.

Mr.Generous

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Steveotwo

Mr.Generous said:

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Really? So Im never going to see a payback spending around 2800 to upgrade to a combi

BarelySentientAI

Steveotwo said:

Mr.Generous said:

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Really? So Im never going to see a payback spending around 2800 to upgrade to a combi

New boilers don't pay back with gas savings (usually) unless the one they replace is very old - think pilot light and non-condensing.

Better controls, or better use of controls, often does because the investment cost is much lower but the gas savings can still be decent.

Steveotwo

BarelySentientAI said:

Steveotwo said:

Mr.Generous said:

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Really? So Im never going to see a payback spending around 2800 to upgrade to a combi

New boilers don't pay back with gas savings (usually) unless the one they replace is very old - think pilot light and non-condensing.

Better controls, or better use of controls, often does because the investment cost is much lower but the gas savings can still be decent.

Current boiler is a Baxi Solo system boiler from 2004 would you upgrade from that? 

ComicGeek

Steveotwo said:

Mr.Generous said:

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Really? So Im never going to see a payback spending around 2800 to upgrade to a combi

You will never get a payback on it (just like window replacements and other 'energy saving' products with good marketing departments). Much better to spend £200 getting updated heating controls and save the rest of the cash. It's likely that any energy saving you would see is from better controls rather than the boiler itself.

A change from system boiler to combi is very much a downgrade. At least with a separate hot water cylinder you can use the immersion to get hot water if the boiler isn't working.

You will end up putting a hot water cylinder back in when you convert from gas combi to air source heat pump in the future.

Complete waste of time and money IMO.

BarelySentientAI

Steveotwo said:

BarelySentientAI said:

Steveotwo said:

Mr.Generous said:

I estimate you'd be spending at least £5 more a year on water and only saving £100 on gas bills.

Really? So Im never going to see a payback spending around 2800 to upgrade to a combi

New boilers don't pay back with gas savings (usually) unless the one they replace is very old - think pilot light and non-condensing.

Better controls, or better use of controls, often does because the investment cost is much lower but the gas savings can still be decent.

Current boiler is a Baxi Solo system boiler from 2004 would you upgrade from that? 

I have just replaced a 1999 Potterton Supreme - but with another heat-only boiler and kept the water tank.

I don't expect a payback on it.