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Corrections/expanding Pipe insulation thread

David Nadle chimed in on the original thread and pointed out I had made an error in interpreting  how the chart was laid out, so I thought I would correct my numbers.  I also expanded them some for typical applications.

Using Brad's Data (corrected) for 2 inch pipe insulation

1inch wastes 60,231 btu/yr

1 1/2 inch wastes 37,793 btu/yr

2 inch wastes 26,727 btu/yr

Assuming $1.00 per therm gas cost ($1.00 per 100,000 btu's) and the cost per 3 foot length QCA posted, I came up with the following simple payback numbers for various conditions.

80% seasonal efficiency:  This would be for modular staged wetback steam boilers with on/off power burners or wetback steam boilers with modulating power burners with a system and boiler capacity closely matched to the actual heat loss (very rare condition).

Simple payback (materials only) for using 1 1/2 inch instead of 1 inch: 4.6 yrs

Simple payback (materials only) for using 2 inch instead of 1 inch: 6.5 yrs

70% seasonal efficiency:  This is more likely for the above boilers in a typical oversized steam system.

1 1/2 inch instead of 1 inch: 4 yrs

2 inch instead of 1 inch: 5.6 yrs

55% seasonal efficiency:  This is a likely  typical efficiency for typical 80% commercial cast iron sectional boiler with open tube type burners in a apartment complex with the boiler matched to the cast iron radiation.  A typical home boiler of this same design is probably slightly better, say 60%, when running cast iron because internal heat gains as a percentage of load are not as high as in an apartment complex and the boiler may have a stack damper to help reduce stand by losses.  This is a typical setup in most homes and many apartments in the Chicago area.

1 1/2 inch instead of 1 inch:3 years

2 inch instead of 1 inch:  4.4 years

For QCA, this last one is probably your condition.

This exercise really does confirm the International Energy Code recommendations.... even the 2 inch payback is under 7 years under the most optimum conditions.   For you folks out east that have even higher fuel costs, your payback is probably much better
The Steam Whisperer (Formerly Boilerpro)

Chicago's Steam Heating Expert

Noisy Radiators are a Cry for Help


  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    edited June 2010
    Thank you!

    Boiler Pro, for calculating the paypack information.  It is VERY helpful to have.  Not only does it make sense for me to get that bare section of pipe insulated, it also presents the opportunity improving performance by increasing the insulation on the rest of the main piping. 

    I am also assuming that if the pipe remained hot during  a 45 minute off cycle, that the time to get the steam to runnout in the mains would be reduced as well.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • David Nadle
    David Nadle Member Posts: 624
    edited June 2010
    Chiming in again

    Boilerpro, I don't wish to knock your analysis, but I'm not a big fan of using payback period to compare projects, because it ignores the time value of money. The best approach is to calculate the net present value (NPV) of the cash flows of each option and choose the one with the highest NPV.

    I created a new chart using my original Knauf and Brad heatloss data, your 80% efficiency parameters, and the most recent yield on the 10 year Treasury note. There is no positive cash flow--you pay for the insulation, then you waste heat every year thereafter. The chart reveals that Knauf's data indicates 1" insulation has the max NPV (but not by much) and Brad's data indicates 1.5" insulation has the max NPV.

    To me, the most striking number is the cost of doing nothing. $40 per foot over ten years. Get those pipes wrapped, people!
  • Thanks, David

    I used to run NPV's all the time when looking at low cost housing for Chicago.  I appreciate your input.  I was wondering if you could run them again at the other efficiencies.  True seasonal 80% efficiency is extremely rare, where 55 to 60% is the norm, IMHO, for most current systems.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
  • David Nadle
    David Nadle Member Posts: 624
    Another chart

    I ran the numbers again at 60% efficiency at different discount rates and changed the span to 30 years. The effect of discount rate on the outcome is interesting. The lower the rate, the greater the benefit to insulating.
This discussion has been closed.