On Wed, 13 Feb 2008 11:53:00 -0800 (PST), wrote:
On Wed, 13 Feb 2008 11:53:00 -0800 (PST), wrote:
But it still doesn't say where the "magic" 41,045 BTU comes from.

Whatever magic it is, googling for 41045 BTU gets *lots* of related PDFs!

Residential ACM Manual: Water Heating Calculation Method, page 8
http://www.energy.ca.gov/title24/200...ACM_APP_RG.PDF
The standard energy in the hot water delivered, 41,045 Btu/day.

Comments on Energy Star Ratings of Home Water Heaters, Page 5
http://www.energystar.gov/ia/partner...nergy_corp.pdf
Using the formula: 41,045 Btu/EF($/Btu)*365

ENERGY STAR Residential Water Heaters: Analysis, page 10
http://www.energystar.gov/ia/partner...iaAnalysis.pdf
Energy consumption estimated using the DOE test procedure.
Based on the following formula: (41,045 BTU/EF x 365)/100,000

LIFE CYCLE COSTS AND SAVINGS FOR WATER HEATING SYSTEMS, page 3
http://www1.eere.energy.gov/solar/us...info_sheet.pdf
The annual delivered energy is 14.98 MMBtu (41045 Btu/day).

OPERATING GUIDELINES AND STANDARDS FOR WATER HEATING SYSTEMS, page 32
http://www.solar-rating.org/standard...OG300SEP02.pdf
Total Energy Draw 43.302 MJ (41,045 Btu)

Consumers Directory of Home Water Heater Ratings, page
http://www.gamanet.org/gama/inforesources.nsf/vAttachmentLaunch/BA8B7EB0CFA8AFEF85256E9000609F9A/$FILE/12-07-oil-rwh.pdf
Using the formula: 41045 Btu/EF($/Btu)*365

Calculating water heater costs for meaningful comparisons
http://www.daviddarling.info/encyclo...ater_cost.html
You need to know the unit cost of fuel
365 × 41045/EF × fuel cost (BTU) = estimated annual cost of operation
365 × 0.4105/EF × fuel cost (therm) = estimated annual cost of operation

Review of hot water heaters
http://www.consumersearch.com/www/ho...rs/review.html
365 X 41045/EF X Fuel Cost (BTU) = estimated annual cost of operation
365 X 0.4105/EF X Fuel Cost (therm) = estimated annual cost of operation

On-demand water heaters, page 8
http://www.naffainc.com/PDF-Files/on...r%20heater.pdf
..41045 x cost per therm of gas x 365 / EF = yearly cost to operate

etc.

I would guess any engineer should be able to tell us what this 41,045 magic
number really is.