A walk around the basement reveals there are many areas of uninsulated pipes, as

Question

A walk around the basement reveals there are many areas of uninsulated pipes, as follows: steam heating pipes- 100' of 3" pipe; domestic hot water (DHW)- 60' of 1 1/2" pipe. You calcualte that insulating the pipes would save 500 gallons (in a normal weather year). Given an energy cost of $1.5 per gallon and an installed cost of $10 per linear foot for insulation of the 3" pipe and $6 per linear foot for insulation of the 1.5" pipe, what would be the sample payback in years for insulating the DHW pipes?

Explanation / Answer

Value of Energy saved =500 X $1.5 =$750

Pipes are cylindrical and heat dissipated is proportional to surface area.

SHP:DHW:: rh:RH

Value of energy saved by DHW = 750 X (60 X1.5)/(60 X1.5+100 X3) =173.077

Cost of insulating 1,5" pipe =6 X60 =$360

Payback in years would be Amount Spent/Amount saved = 360/173 =2.07 years

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