Bill Luecke: Utility Use Deep Dive

1. Introduction

About five years ago, I noticed that our water bill seemed to be increasing beyond what I thought that the rate of inflation was. This observation led me to do a deep dive into our utility consumption.

This deep dive was possible because, as a hoarder, I had saved almost every utility bill we've ever received at 7316 Allan.

The deep dive comprises three sections: Water, Gas, and Electricity. Within each section, plots show the total cost in both absolute and inflation-adjusted dollars. Each section attempts to determine the major sources of the usage and cost, and provides recommendations for reducing usage.

2. Water

2.1 Usage

2.1.1 General usage notes

Values of usage for appliances come from the manufacturer specification. For toilet use I tracked the number of flushes over a three-week period and effectively doubled them, because we have two toilets. I estimated the length of the shower, but measured the flow rate of our low-flow shower head.

Activity	Use	Frequency
	gal/day	per day
Bill showers	5	0.57
Sandra showers	17	0.57
Bill toilet	4.5	3.53
Sandra toilet	2.6	2.02
Dishwasher	3.4	0.57
Clothes washer	11	1.00
Total	43.6

Figure 1 below shows the daily water consumption since 1992. Colors and symbols identify the season. The annotations indicate major life changes and installation and use dates of water-consuming appliances.

Over the past thirty years, Sandra spent 2 years living full-time in Albany, and has stayed in Baltimore first four or five days a week, but since 2023, three days per week.

Figure 1. Water usage since 1992

2.1.2 Findings

Our water use has generally decreased from about 80 gal/day to the present 40 gal/day from the 1990s to present.
None of the high-usage quarters (Usage>100 gal/day) were in the winter quarter.
Note the general drop in usage 2005—2007 when Sandra lived in Albany.
The largest drop in usage correlates with the replacement of the old toilet in 2017.
Despite Luecke post-retirement, usage remains low.

2.1.3 Conclusions and Inferences

The new washer (11 gal/wash vs. 35 gal/wash) canceled out by Luecke retirement.
Heavy usage in the 1990s could be due extensive lawn watering.

2.1.4 Recommendations

Very little extra efficiency on water use is possible.

2.2 Cost

2.2.1 Background

Water bill is issued quarterly, includes charges for both supply and sewer.
Water is billed in units of 1000 gallons.
In 2014, the Virginia supreme court mandated that Falls Church City sell its water system, which supplied much of Northern Virginia inside the beltway, to Fairfax Water Authority.
Our sewage is handled by the AlexRenew plan on Cameron Run in Alexandria.

2.2.2 Rate and Total Cost

Figure 2 shows the absolute and inflation-adjusted cost of water. Annotations denote the periods in the change in ownership of the water company (see links below). Initially, I had thought that the increase in water rate was due to the supreme court-mandated sale of Falls Church Water to Fairfax Water Authority.

Figure 2. Absolute and inflation-adjusted water rate

Figure 3 shows the actual billed cost of water.

Figure 3. Absolute and Inflation-adjusted quarterly water cost.

2.2.3 Findings

Sewage disposal is main driver of cost after 2008.
Sewage disposal costs have outstripped the rate of inflation by 4x since 2008.
Inflation-adjusted Water supply costs have not changed in thirty years.

2.2.4 Conclusions and Inferences

The payback time on a 2 gal.flush toilet over a 4 gal/flush toilet, assuming that the toilet cost is $200 and you install it yourself is only 470 days: $150/((7.1 flushes/day * 2 gal/ flush) * $0.03/gal). Paying a plumber $300 for the installation drives the payback time to about 3.2 years, which is still a rapid return on investment
Despite our roughly 2/3 reduction in water use, our water bill has doubled since 1995.
It seems reasonable that sewage costs have increased, presumably due to reduced tolerance for dumping raw sewage into the Potomac River.
I had originally thought that the court-ordered sale of the water company to FC drove the price increase, but the sewage price increases, which had always been controlled a different authority, started in six years before the sale.

2.2.5 Links

This website http://www.virginiaplaces.org/watersheds/fairfax-fallschurch.html summarizes the history of the Fairfax Water Authority/Falls Church Water Company battle.

Sewage from our neighborhood goes to the AlexRenew treatment plan in Alexandria. Maps here: https://www.fairfaxcounty.gov/publicworks/wastewater/wastewater-treatment

3. Gas

3.1 Introduction

We use three gas-fired appliances: a stove, a water heater, and a 90% efficient furnace, which was installed in 1995.

3.1 Climate change in Northern Virginia

3.1.1 Summary plots

For a day, the heating degree days, HDD is defined as

HDD = 65 ℉- (Tmax+Tmin)/2

If the average temperature is above 65 ℉, HDD=0.

Typically, HDD is a measure of the heating requirements in a given location.

Figure 4: Heating degree days per year since 1999.

3.1.2 Findings

The number of heating degree days, HDD per year has decreased about 20% since 2000.

3.2 Gas Usage

Figure 5: Gas use in therms in months where it is likely that the furnace is off.

3.2.1 Findings for gas use

Figure 5 shows that installation of a new water heater only partially reduced cut the gas use during months with no heat from about 6 therms/month to 4 therms/month.
Gas, presumably for water heating, rose during the COVID-19 work-from-home era.
Gas use has remained at about 4 therms/month even though Sandra is only working and staying 3 days /2 nights per week in Baltimore, and William is retired.
I have no explanation for high usage 2008-2014, although that era was near the end of life of our original water heater, which came with the house in 1992.

3.3 Gas Cost

3.3.1 Summary Plots

Figure 6 shows the yearly total gas cost (heating+hot water+cooking) in both absolute and inflation-adjusted dollars

Figure 6: Yearly gas cost

3.3.2 Findings

In absolute terms, the cost for gas has remained effectively unchanged for the last 25 years.
In inflation-adjusted terms, the cost for gas has decreased almost 50%, partially due to the reduction in heating demand.

3.3.3 Discussion and Inferences

Of the $750 total per year charge for gas, $70 is cooking and hot water (4 therms * $1.5/therm) and $680 is for heat.
In 2025 dollars, the total charge for heat over a 20 year expected life of a HVAC system is $14K. That makes it hard to justify significant extra costs for energy efficiency on a new HVAC system.

3.4 Gas Rate

3.4.1 Summary Plots

Figure 7: Gas cost rate since 2000.

3.4.2 Findings

Gas actually costs about 20% less in 2025 than in 2010 in inflation-adjusted dollars.

3.5 Notes

I cannot locate any gas bills before 1999.
Question. What is the base load of the water heater if you never draw any water out of it?
The rate plots include the monthly "system charge" $12.40. Electricity and Water build this charge into the rate.

4. Electricity

4.1 Usage

Figure 8 shows electricity usage per month since 1992. Yellow bands denote summer months (June 21-Sept 21). Annotations describe major electric appliance installation and use periods.

Notes

Until 2003 we used the dryer that came with the house in 1992. To hold the door shut we used a horseshoe magnet.
After replacing the refrigerator during the 1999 kitchen rebuild we moved the original pre-1992 refrigerator to the basement. Neither WL or SH can remember when we got rid of it, though.

Figure 8: Electricity used since 1992.

4.1.1 Findings

General trend: 2X current energy use during 1997 - 2004.
The current energy use is (300 < E < 400) kWh/mo
Most high-use months occur in the summer, presumably correlated with A/C use.

4.1.2 Analysis

4.1.2.1 Lighting

Various internet sources indicate that in 2002, 85 % of bulbs in use were incandescent. I estimate the bulb distribution and duty cycle for two eras.

- 1992 usage: 390 kWh/mo from 27 incandescent + 4 T12

- 2025 usage: 150 kWh/mo from 33 LED, 3CFL, 4 T12, 8 T8, and 6 48in LED

Energy use estimated that the lights are on 1/4 of the time.

The longer we have lived here, the more lamps we have installed.

4.1.2.2 Other Electrical use

I estimate the following usage from manufacturer specification sheets

50 kWh/mo Refrigerator 50kWh/mo = 0.07 kWh/hour
25 kWh/mo Dryer
36 kWh/mo Cable modem/Wifi/DVR
A/C 3kW running = 35kWh/day running 12 h/day, 5 days month = 170kWh/mo

4.1.2.2.1 Notes

Wifi/cable modem consumes 50W 24 h/day (measured)
Dryer use estimated from 13 months of hourly electric usage. The dryer signal is a 1 hour spike at 3.2kW, which occurred 88 times. WEL air-dries most of his clothing already.
Nighttime energy usage is 0.1 kWh per half hour = 0.2 kwH/h = 200 W 4.8kWh/day = 144 kWh/month.

4.1.2.2 Usage Patterns

Figure 9 shows the energy used during selected months where no A/C use would have occurred.

The minimum power use is in May and November, when lighting use would be low.

Figure 9: Energy use during months where no A/C was used.

Figure 10 shows a snapshot of the hourly energy consumption for one week in 20204.

The nighttime base load is 0.2 kwH/h = 200W, which presumably includes the refrigerator consumption of 0.07kwH/h per hour.

Figure 10: Energy use during the week of 2024-04-28.

4.1.3 Inferences and Conclusions

Finishing the replacement of T8 and T12 fluorescent bulbs with LED bulbs would reduce the power need about 200 W and the use about 40 kWh/mo, which is 10% of the total.
Very few other approaches to reducing electricity consumption appear to exist, beyond being more disciplined about shutting off lights.

4.2 Cost

Figure 11 shows the absolute and inflation-adjusted cost of electricity since 1992

Figure 11. Electricity cost per month.

4.3.1 Findings

Because of energy efficiency, electric bill in absolute dollars hasn't change in thirty years.

4.3 Rate

Figure 12 shows the cost rate of electricity since 1992.

The inflation-adjusted rate has decreased (!) since 1992 from $0.10/kwH to $0.075/kWh.

Figure 12: Electricity Rate since 1992.

* Insurance

Pages

Monday, July 7, 2025

Utility Use Deep Dive