Cost of keeping Baxi 105 Instant boiler on overnight

My new boiler is a Baxi 105 Instant with two zones upstairs and downstairs which are both off from 2200 hrs to 0600 hrs leaving the hot water on. It maintains about 7 l of primary hot water hot throughout the night so that it provides ?instant? hot water as soon as a hot tap is turned on. June has used a combi boiler elsewhere and hated the wait for hot water to arrive at the tap while the combi lit up, especially in the summer. As far as she is concerned the instant feature works fine.

Curious to know how much power this was using I read the gas meter at

2230 and again at 0530 this morning, the display is split as shown below.

Gas reading 22:30 21/1/07 7681 15 . 1 cu ft Gas reading 05:30 22/1/07 7681 20 . 6 cu ft

That is 5.5 cu ft in a 7 hr night.

Looking at the back of my gas bill from Scottish Power the rather strange calculation required is:

5.5 * 2.83 * 39.9 * 1.022640 / 3.6 = 176.4 2.83 to convert from imperial to metric 39.9 = Calorific value 1.022640 = Volume Correction 3.6 to give Kw Hrs

176.4 / 1000 = .176 Kw hrs

1000 because it looks as if only the first 4 figures are read

.176 / 7 = .025 Kw

.025 / 1000 = 25 watts

cost for each night .176 * 3.727 = 65.5 pence price per KWhr = 3.727

Cost per year of keeping the boiler on overnight = 65.5 * 365 = GBP 239.4

Probable real cost GBP 100 per annum.

Only part of the GBP239 is lost, that in the summer, and parts of spring and autumn, when the central heating is off and house gets too hot on solar heat gain plus losses of TVs freezers etc. etc., and windows/doors are left open to cool the house. say a real cost of GBP 100 per annum.

The house is very well insulated, at night with an outside temperature of 0 Deg C the bedrooms only fall 2 deg C during the night and the kitchen only 5 deg C (must improve the insulation of the kitchen)

Reply to
Dave Fawthrop
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Surely 25W x 8 hours x 3.727p/1000 (w-kW) = 0.75p per night ?

Reply to
Tony Bryer

Are you reading your meter correctly? Most Cu Ft meters only have 4 "readable" numbers and maybe another two max which are fractional.

Reply to
Psst

|On Mon, 22 Jan 2007 16:34:08 +0000, Dave Fawthrop | wrote: | |>My new boiler is a Baxi 105 Instant with two zones upstairs and |>downstairs which are both off from 2200 hrs to 0600 hrs leaving the hot |>water on. It maintains about 7 l of primary hot water hot throughout |>the night so that it provides ?instant? hot water as soon as a hot tap |>is turned on. June has used a combi boiler elsewhere and hated the |>wait for hot water to arrive at the tap while the combi lit up, |>especially in the summer. As far as she is concerned the instant |>feature works fine. |>

|>Curious to know how much power this was using I read the gas meter at |>2230 and again at 0530 this morning, the display is split as shown below. |>

|>Gas reading 22:30 21/1/07 7681 15 . 1 cu ft |>Gas reading 05:30 22/1/07 7681 20 . 6 cu ft |>

|Are you reading your meter correctly? Most Cu Ft meters only have 4 |"readable" numbers and maybe another two max which are fractional.

Yes! Absolutely sure! the numbers are grouped four in black, two in red and one as a clock face with one hand. I assume that only the four are read, the remainder are for accurate differential readings such as I am using.

Also a hand on the casing confirms that the final wattage figure is in the right ball park.

Reply to
Dave Fawthrop

Gas bills use units of 100 cubic feet. You've used only 0.055 units overnight, and each unit is roughly 30kWh

You mean 0.65p?

However 0.055 units (of 100 cu ft) would be 1.76kWh. The overnight cost is then 6-7p.

Divide the cubic feet on the meter by 100 to get the units used on the bill (ignore the final tenths figure).

Bart

Reply to
Bart

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