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 Hrs176.4 / 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)