Estimated consumption for Greenstar 38CDi

[joewa]

I've had a feeling for a while that our brand new Greenstar 38CDi is using more gas than it should.

A brief overview we live in a 3 bed semi, roof insulated to 150mm and no wall cavities. Each room has one single panelled radiator (older system) with zoned Evohome TRVs. In simple terms downstairs is off at night and upstairs is on, vise versa in the day.

We have two showers and one kids bath a day and the water is supplied at 16 Litres per minute. New monthly units used approx 300, or £110 just for gas. outside temp has been an average of 7oC this week.

We bought the house in October, moving from a 2 bed terrace where the heating was on at 20 degrees 24/7. Cost there per month was £50 per month. Boiler there was a 15 year old Greenstar 27HE

To me, more than double the amount per month for a house only moderately larger seems odd. I asked the WB engineer about this and he said the boiler should use a similar amount of gas as the 38CDi has the same size heat exchanger as the 27HE.

Energy company estimations for our house show that we should be using 13500 KWH but we are actually using 37000!

Is there something wrong with our boiler or perhaps the energy company's calculation of our calorific value?

I would also like to know the estimated KWh under normal use for our boiler to help me get my head round this!

 

[gigz]

You can't possibly get a definative answer on the forum. Your boiler uses (or should do) approx 4M/3 per hour at full pelt. You won't be using that. I would get a safety check done, this will tell you what your boilers using, will also get a tightness check in case you have a gas leak.

 

[muggles]

Are you sure you / your energy company haven't confused metric and imperial readings on your gas meter?

Your boiler is massively oversized for your house's heating requirement and is therefore quite likely to be cycling on and off a lot. This will use considerably more gas than a boiler that is correctly sized for the property. You have, I'm afraid, bumped into one of the major disadvantages of having a combi, especially a high-output one

 

[Agile]

If the cost concerns you then why are you showering at16 li/min?

To me that seems very extravagant indeed.

I am naturally frugal but manage very well at just 8 li/min!

Tony

 

[Gasguru]

The old £50 per month (that sounds too low, are you sure you hadn't built up a surplus before) was derived from several years at the previous property.

You've moved into the new property at the start of the Winter season...so the gas consumption will be high. In a few months it will drop down considerably and a sensible average consumption can be calculated.

Check the systems balanced and turn off pre-heat if you don't really need it, fit a flow limiter to the shower head...8 litres/min is ample, turn the TRVs/stat down...the majority of homes I see are ridiculously hot.

 

[Agile]

Check the systems balanced and turn off pre-heat if you don't really need it, fit a flow limiter to the shower head...8 litres/min is ample, turn the TRVs/stat down...the majority of homes I see are ridiculously hot.

That's what I find Geoff, 8 li/min is adequate.

But soon Dan will be along to tell us that 16 li/min is a minimum for his comfort!

Tony

 

[joewa]

Thanks for all the replies. The boiler was chosen with the future in mind. We will add another bedroom and ground floor room in the next few years, in addition to the back half of the garage. That and the fact we have two bathrooms meant that the Worcester calculator recommended this boiler.

I think I can adjust the threshold of where the boiler fires up on the evohome to reduce the number of cycles. I'm monitoring the cycles with a Belkin Wemo so I'll soon know if it's helped. I'll also reduce the flow from the stopcock.

Thanks for all the help.

 

[Dan Robinson]

You gotta love those online calculators written by ********s.

 

[joewa]

 

[joewa]

Thinking about this I have a powerful boiler doing less work than capacity. How can I mitigate this? Perhaps turn the CH temp down so the boiler takes longer to heat rooms using less gas? As I understand it 'short cycling' means the boiler is running uneconomically anyway.

 

[muggles]

Short cycling is very uneconomical. It is possible to reduce the boiler's max output but it requires considerable shenanigans with the installer settings to achieve

 

[Dan Robinson]

Wooshitter Botch have terrible modulation ranges so you're pretty much screwed.

Combis are not suitable for multiple bathrooms no matter what the 'tards working for the manufacturer like to try and get away with in their marketing flannel.

 

[steve32]

Check the systems balanced and turn off pre-heat if you don't really need it, fit a flow limiter to the shower head...8 litres/min is ample, turn the TRVs/stat down...the majority of homes I see are ridiculously hot.

That's what I find Geoff, 8 li/min is adequate.

But soon Dan will be along to tell us that 16 li/min is a minimum for his comfort!

Tony

I am with Dan on this min 16 li/min for a good shower

 

[Dan Robinson]

Chopped my thermal store with 100kW plate in for a 150 litre unvented cylinder with 300 litre accumulator.


Still hovering around 22 l/min on my shower But more importantly, the accumulators have made it possible to run 2 showers at the same time at around 18 l/min.

Balls to having a combi

 

[Agile]

Don't you recycle all that used shower water Dan to flush your special toilets?