Crazy gas bill - Whats going on

carlsagen

7 day readings sounds like a good idea. Ive got nothing else to do. Ill report back. !

Talldave

For comparison I just looked up what we used in the 7 Nov to 30 Mar period, during which you used around 23,400kWh and it was 28,000kWh for a 5 bed detached place with 10 radiators (23C day / 22C night) and 3 UFH zones (23C day / 18C night) including a large kitchen and a 300L hot tank. This place runs quite happily with a 30kW boiler.  Although we've only been here 8 months, annual gas projection is 44,000kWh.  I am not an expert but I'm wondering if your 40kW boiler is over-specified and perhaps isn't running efficiently?

MWT

Your usage is high, but not impossibly so, it looks likely to be accurate, just expensive.

For comparison, over the period between your reading on 7th Nov. and 30th Mar. you averaged 100kWh/day.

For our well insulated 5 bedroom house with 11 radiators and temperature set to 20C, cylinder based hot water, we averaged 68kWh/day

RelievedSheff

carlsagen said:

Talldave said:

What times & temperature are set for Hot Water. Your consumption over 5 winter months is maybe a bit high for that size place. What's insulation like?  Double glazed?

Heating and hot water set to max. Its a hot water on demand boiler rather than water tank.
Double glazing throughout. 150mm kingspan roof insulation in the new part of the house that has UFH. 50mm kingspan in foof of old house.. Old house is rubble filled stone walls (no cavity) 
Heating thermostats set to 18 degrees on the timer. 

If this is a new condensing boiler and you have it set to max for the central heating then it is not running as efficiently as it should be. You need to knock it down to about 65 degrees or so.

Also if the boiler is over sized for the house if your radiators are fitted with TRV's leave them all open and on full to lower the return water temperature. The return water temperature needs to be around 55 degrees to get the boiler to work at is most efficient in condensing mode.

We have a similar problem with our 30kW boiler in a small 3 bed highly insulated new build. If we turn down the TRV's in any of the rooms the boiler will not run in condensing mode. Now that we have worked this out though the heating works a treat and runs very economically.

carlsagen

RelievedSheff said:

carlsagen said:

Talldave said:

What times & temperature are set for Hot Water. Your consumption over 5 winter months is maybe a bit high for that size place. What's insulation like?  Double glazed?

Heating and hot water set to max. Its a hot water on demand boiler rather than water tank.
Double glazing throughout. 150mm kingspan roof insulation in the new part of the house that has UFH. 50mm kingspan in foof of old house.. Old house is rubble filled stone walls (no cavity) 
Heating thermostats set to 18 degrees on the timer. 

Also if the boiler is over sized for the house if your radiators are fitted with TRV's leave them all open and on full to lower the return water temperature. The return water temperature needs to be around 55 degrees to get the boiler to work at is most efficient in condensing mode.

Really? The plumber balanced and since ive tweaked the TRVs as some rooms get spanking hot and other cold. If I did that it would be uncomfortably hot in the bedrooms. The room that takes the longest to warm (living room 5m x 5m) rad has its trv on maximum 

I have also experimented with lowering the central heating temperature using the dial at the boiler but found the boiler ran for longer and the radiators were noticeable cooler to the touch so I turned it back up. My hot water isn't on max, its set to 55. Ive dialled the boiler CH down a bit from its 83 to 70 to see if it makes any difference. 

I have calculated the BTU off the radiators to make sure they are accurate for the room size and property type and they are all over specified. I do think though there is an element of the type of house taking longer to warm. I prob say it takes a couple of hours for it to warm from say 10 degrees to 17 when I come home. it would take an awful lot longer to get to 22. I just presume the external walls being stone and rubble filled just suck it all up. 

Being a grade II listed cottage I have to have wooden windows (though they are double glazed) also the front door cant be composit or upvc. As such the wood shrinks and expands during the year leaving gaps either side and is a huge source for drafts to the front room. I guess I need to plug this leak somehow (self adhesive draft strips are no use). Or stick a wood looking door in and cross my fingers. 

RelievedSheff

carlsagen said:

RelievedSheff said:

carlsagen said:

Talldave said:

What times & temperature are set for Hot Water. Your consumption over 5 winter months is maybe a bit high for that size place. What's insulation like?  Double glazed?

Heating and hot water set to max. Its a hot water on demand boiler rather than water tank.
Double glazing throughout. 150mm kingspan roof insulation in the new part of the house that has UFH. 50mm kingspan in foof of old house.. Old house is rubble filled stone walls (no cavity) 
Heating thermostats set to 18 degrees on the timer. 

Also if the boiler is over sized for the house if your radiators are fitted with TRV's leave them all open and on full to lower the return water temperature. The return water temperature needs to be around 55 degrees to get the boiler to work at is most efficient in condensing mode.

Really? The plumber balanced and since ive tweaked the TRVs as some rooms get spanking hot and other cold. If I did that it would be uncomfortably hot in the bedrooms. The room that takes the longest to warm (living room 5m x 5m) rad has its trv on maximum 

I have also experimented with lowering the central heating temperature using the dial at the boiler but found the boiler ran for longer and the radiators were noticeable cooler to the touch so I turned it back up. My was isn't on max, its set to 55. Ive dialled the boiler down a bit from its 83 to 70 to see if it makes any difference. 

I have calculated the BTU off the radiators to make sure they are accurate for the room size and property type and they are all over specified. I do think though there is an element of the type of house taking longer to warm. I prob say it takes a couple of hours for it to warm from say 10 degrees to 17 when I come home. I just presume the external walls being stone and rubble filled just suck it all up. 

Yes Really!

For a condensing boiler you need to run it at low temperature and have a low return water temperature to force it into condensing mode. Only turn it up in really cold weather. It does very much sound as though your boiler is never getting into condensing mode hence the higher than expected bills.

It sounds counterintuative to lower the boiler temperature and have it running for longer but it really does work. Yes the radiators will be cooler to the touch than when it is on full.

Talldave

@carlsagen Use a programmable thermostat with optimum start and it will learn when to turn the boiler on in order to reach your target temperature at the desired time. So if you reduce the radiator temperature, it'll learn within a couple of days that it needs to come on earlier. 
@RelievedSheff Interested to learn more about getting condensing boilers "into the zone". Any recommended reading for dummies?

tim_p

Talldave said:

@carlsagen Use a programmable thermostat with optimum start and it will learn when to turn the boiler on in order to reach your target temperature at the desired time. So if you reduce the radiator temperature, it'll learn within a couple of days that it needs to come on earlier. 
@RelievedSheff Interested to learn more about getting condensing boilers "into the zone". Any recommended reading for dummies?

Me too, how do you know, for sure, if your boiler is condensing ( and conversely when it’s not)??

RelievedSheff

There is plenty about in on the internet although you have to sort out the weeds from the chaff of course.

The theory is pretty simple in that you need a low return water temperature of about 55 degrees. Most boilers will have a symbol (it is an "e" on ours) to show you roughly where the ideal condensing temperature is on the boiler temperature control. We need to knock ours down a couple of degrees further as the boiler is too big for the system. You will also get the little tell tale poofing of steam from the external flue and depending on the boiler it may put a symbol on the display to say it is in condensing mode.

tim_p

RelievedSheff said:

There is plenty about in on the internet although you have to sort out the weeds from the chaff of course.

The theory is pretty simple in that you need a low return water temperature of about 55 degrees. Most boilers will have a symbol (it is an "e" on ours) to show you roughly where the ideal condensing temperature is on the boiler temperature control. We need to knock ours down a couple of degrees further as the boiler is too big for the system. You will also get the little tell tale poofing of steam from the external flue and depending on the boiler it may put a symbol on the display to say it is in condensing mode.

Get plenty of steam, don’t remember getting that from the old (pre-condensing era) boiler. 

Don’t think the boiler shows any specific symbol for anything other than a flame! (Vaillant ecoFITpure) but will dig out the manual and RTFT!
Thanks