Tuesday, October 23, 2012

Making Sense Of Gas Usage History

My natural gas utility is able to provide customer gas usage histories going back six years. This can be requested in a phone call or in an online account query. I thought I would simply study annual totals, and they do have meaning, but learned I must work with each month's numbers. Just ask for the monthly list, and do all math yourself. I offer a detailed example for one customer, to follow results of substantial sealing and insulation improvements in the winter of 2010. About half of the history will precede improvements, and half will follow.

Please experience as much of the job as you wish, in job photo albums. Some elements of this job have been shared in older posts, for example, discussion of soffit baffles.

At 11/4/2014, look for further discussion of this job , with charts of gas usage for a 23 year span. 

Garage Attic Ladder  

Work actually began in 2008, with installation of a first  MidMade attic ladder in a newly-replaced garage drywall ceiling. 

House Attic Ladder   

Here I coped with replacement of a defective door limit arm. My enthusiasm for MidMade ladders was not reduced.

House Attic Prep 

Added top-layer insulation was crumpled kraft-faced. For intimate placement, I stripped all facing. All pink batts fit in a much-more-thorough base course overflowing the tops of 2x4 truss bottom elements.

Please know this was not a best effort with flooring of a truss attic. Please find many better examples at this blog.

House Attic Baffles & Insulation 

This attic is now well-ventilated, over thorough R40 insulation. Found batts generally blocked soffit vents.

This is at February 23, 2010.

Middle Attic Insulation & Decking  

Here is a small attic accessible through the garage. 

Crossing layers of R15 will slow large heat losses through bedroom walls. 

Why would one stop at R15?

This is at March 15, 2010.

Here is an Excel chart of the natural gas usage in this home:

Do you see change starting in February, 2010? Here are monthly numbers, and annual totals July through June. I see annual savings of up to $600 per year. Maybe as little as $200. It is hard to work past variables of weather and lifestyle. We all should have the privilege of such after-job monitoring. It is a bit of work requiring ownership and modest skill, in Excel. A gas utility might  send charts and tables annually in July, and/ or at the time a rebate is paid. Twelve-month average therms per day, as charted in paper bills, are not useful in seeking a bigger picture. I wish I had known to seek a six years history in 2010, to add to this time line. Many of us keep a long history of bills. This customer could readily help me look further back, with retained or logged monthly statements.

I have bothered to predict savings, and results are presented with analysis, here
In summary:

Main Attic Insulation: $61/yr.
Main Attic Floor Sealing: $200/yr
Middle Attic Insulation: $30/ yr

Total: $291 per year, at $2 per therm gas cost. More than two thirds is from sealing that has no impact on readings of a blower door. A blower door is never the measure of effective floor sealing.

Savings from weatherization investments are reduced  at subsidized, not real fuel cost, $1.15 per therm for natural gas in this home, in 2012. 

There is a corresponding saving of air handling electricity cost. My own gas and electricity usage numbers suggest about $20 per month additional electricity average in the heating season, vs $35 per month for natural gas. 

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