[Greenbuilding] : water heater blanket payback?

[nick_pine]

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-------- Original message --------
From: greenbuilding-request at lists.bioenergylists.org 
Date: 04/10/2016  2:00 PM  (GMT-05:00) 
To: greenbuilding at lists.bioenergylists.org 
Subject: Greenbuilding Digest, Vol 68, Issue 7 

> How long would it take this $21.57 R10 water heater blanket to pay for itself with electricity at $0.15 per kilowatt hour?

With no blanket, 2070 Btu/day = 24h(135-67.5)G, which makes G = 1.28 Btu/h-F = A/Rv, so Rv = 14.6sqft/1.28 = R11.42. Adding the R10 blanket makes Rv = R21.42 with a 1104 Btu daily heat loss.
The difference is 974 BTU (0.28 kWh) per day worth 0.28x0.15 = $0.0426, so the pay back is $21.57 divided by 0.0426 = 506 days, ie 1.39 years.
Nick 
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