Water Meter system boiler vs combi

vacheron

One solution is to do as hotels do which is that they have the hot water constantly circulating in a pipe loop up and down the corridors with short spurs off to each room.

This is how you have piping hot water available to your hotel room (even at the end of a long corridoor) just a second or two after turning on the tap.

The only downside is the constant heat losses and pump operation, but at least there are solutions for the impatient in large houses with plenty of spare money!   

Steveotwo

FreeBear said:

Albermarle said:

casper_gutman said:

We have a combi and the layout means the bathroom taps get hot water very quickly, but the kitchen, utility and downstairs loo take 20-30 seconds. It's only really an issue when you really need hot water for washing up etc, as for a quick handwash or rinsing some fruit etc cold is fine. I just wish I could train the rest of the family to use the cold tap for such things. It's so pointless turning on the hot tap and making the boiler fire up if you're not even going to be using the water for long enough for it to run hot!

It is the same issue if you have a hot water tank. It is not related to whether it is a combi or not, but to the length of the pipe runs.
You also get the same problem with people turning the hot water tap on for a short time. The boiler does not fire up, but the already heated hot water just cools off in the pipework and energy is wasted.

Yer, but... That heat isn't wasted as it helps to heat the house - A rather pointless argument in my book as the heat is going in to spaces that are not used (under floorboards & behind cabinets). the other issue with long runs of pipe for DHW is the temperature drop - You want 60°C water at the kitchen tap, the boiler may need setting to 65°C. Then it is way too hot for the bathroom taps, so you then need thermostatic valves or some way to turn the DHW temperature down.

I'm inclined to turn off DHW at the kitchen sink via the isolation valve and boiling a kettle when the washing up needs doing.

Does that work out cheaper using the kettle?

FreeBear

Steveotwo said:

FreeBear said:

Albermarle said:

casper_gutman said:

We have a combi and the layout means the bathroom taps get hot water very quickly, but the kitchen, utility and downstairs loo take 20-30 seconds. It's only really an issue when you really need hot water for washing up etc, as for a quick handwash or rinsing some fruit etc cold is fine. I just wish I could train the rest of the family to use the cold tap for such things. It's so pointless turning on the hot tap and making the boiler fire up if you're not even going to be using the water for long enough for it to run hot!

It is the same issue if you have a hot water tank. It is not related to whether it is a combi or not, but to the length of the pipe runs.
You also get the same problem with people turning the hot water tap on for a short time. The boiler does not fire up, but the already heated hot water just cools off in the pipework and energy is wasted.

Yer, but... That heat isn't wasted as it helps to heat the house - A rather pointless argument in my book as the heat is going in to spaces that are not used (under floorboards & behind cabinets). the other issue with long runs of pipe for DHW is the temperature drop - You want 60°C water at the kitchen tap, the boiler may need setting to 65°C. Then it is way too hot for the bathroom taps, so you then need thermostatic valves or some way to turn the DHW temperature down.

I'm inclined to turn off DHW at the kitchen sink via the isolation valve and boiling a kettle when the washing up needs doing.

Does that work out cheaper using the kettle?

3-4l of water in the pipe, plus another 7l in the boiler - This all needs to be heated up before getting hot water at the tap. Boiler efficiency is much lower when heating DHW, perhaps as low as 70% if you want real hot water.

Assume incoming water is at 14°C, and is heated to 60°C - Each litre will require 0.05kWh of energy. So 5l out of the tap will use ~1kWh of gas.

Heat just 5l of water in a kettle (which is almost 100% efficient), you only consume ~0.25kWh of electricity.

Gas is about quarter the price of electricity, so using the numbers above, there isn't much difference in cost. Once you factor in servicing costs of the boiler, a kettle starts to look (fractionally) cheaper. Then there is the replacement cost - A kettle for <£20 or a boiler for ~£3K...

Albermarle

Steveotwo said:

FreeBear said:

Albermarle said:

casper_gutman said:

We have a combi and the layout means the bathroom taps get hot water very quickly, but the kitchen, utility and downstairs loo take 20-30 seconds. It's only really an issue when you really need hot water for washing up etc, as for a quick handwash or rinsing some fruit etc cold is fine. I just wish I could train the rest of the family to use the cold tap for such things. It's so pointless turning on the hot tap and making the boiler fire up if you're not even going to be using the water for long enough for it to run hot!

It is the same issue if you have a hot water tank. It is not related to whether it is a combi or not, but to the length of the pipe runs.
You also get the same problem with people turning the hot water tap on for a short time. The boiler does not fire up, but the already heated hot water just cools off in the pipework and energy is wasted.

Yer, but... That heat isn't wasted as it helps to heat the house - A rather pointless argument in my book as the heat is going in to spaces that are not used (under floorboards & behind cabinets). the other issue with long runs of pipe for DHW is the temperature drop - You want 60°C water at the kitchen tap, the boiler may need setting to 65°C. Then it is way too hot for the bathroom taps, so you then need thermostatic valves or some way to turn the DHW temperature down.

I'm inclined to turn off DHW at the kitchen sink via the isolation valve and boiling a kettle when the washing up needs doing.

Does that work out cheaper using the kettle?

Probably very little in it, pennies per week probably.
However using the kettle is less wasteful of water.

BikingBud

With the trend for boiling water taps in the kitchen now would it be worth considering not putting hot water to the kitchen sink at all?

If the domestic management "need" one it seems like its going in anyway and the DHW system can then be much more compact, reduced pipework and boiler close to bathroom etc.

FreeBear

BikingBud said:

With the trend for boiling water taps in the kitchen now would it be worth considering not putting hot water to the kitchen sink at all?

Have you seen the price of a Quooker ??

Fortunately, cheaper options exist, but even at the budget end of the market, £225 is a good chunk of money to spend.

BikingBud

FreeBear said:

BikingBud said:

With the trend for boiling water taps in the kitchen now would it be worth considering not putting hot water to the kitchen sink at all?

Have you seen the price of a Quooker ??

Fortunately, cheaper options exist, but even at the budget end of the market, £225 is a good chunk of money to spend.

Get that but sometimes there are items that are "non-negotiable" due to the extreme fashion influence, islands, pot fillers, stone worktops etc. Once they are "in" the design the function provided by other elements may not be necessary and could offset the expense a little. 

JohnSwift10

When I had a hot water tank I used 3kWh a day for the pilot light and 7 kWh a day to heat the water.
After I got a combi boiler my daily use (in the summer without the heating being on) is about 11 kWh a day so no difference in gas usage overall  but I am using more gas to heat the water water.

As for water use I have no idea as I live in Scotland and we don't get the option to have water meters.and I am paying £667.81 a year for water used by 2 OAPs

ThisIsWeird

JohnSwift10 said:

When I had a hot water tank I used 3kWh a day for the pilot light and 7 kWh a day to heat the water.
After I got a combi boiler my daily use (in the summer without the heating being on) is about 11 kWh a day so no difference in gas usage overall  but I am using more gas to heat the water water.

Not sure these figures add up.

With your old hot tank system, if you'd had a boiler that didn't have a pilot light (like all boilers these days), then you would only have used around 7kWh per day to heat your water? And your combi - which doesn't have a pilot light - uses 11kWh for essentially the same job? That can't be right.

If your figures are correct, I can only guess you are using a lot more hot water.

All other things being equal, a combi should theoretically use a little less energy than a stored water system, simply because a stored hot water tank will lose some heat through its skin over the day.

Steveotwo

JohnSwift10 said:

When I had a hot water tank I used 3kWh a day for the pilot light and 7 kWh a day to heat the water.
After I got a combi boiler my daily use (in the summer without the heating being on) is about 11 kWh a day so no difference in gas usage overall  but I am using more gas to heat the water water.

As for water use I have no idea as I live in Scotland and we don't get the option to have water meters.and I am paying £667.81 a year for water used by 2 OAPs

So the combi is less efficient? We didn't have a meter before we moved and we paid £24 a month, we have moved into a house with a meter and they have immediately placed us on £42 a month while they gauge how much they want us to pay