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## Gas Bill Review - How much Did I save using my Navien tankless waterheater?

How much money was saved over the last 2 months tankless v.s. On-Demand Navien NR240-A?

Data for the last 2 months is now in. The short answer is my gas consumption dropped by: 49.8%

In absolute terms, it works out to .96 cubic meters (33.9 cubic feet) per **day**.

The Details:

First the water heater that was removed was a GSW 5G50ENA-03, which was a 182 Liter or 41.6 Imperial gallon tank with 45000 BTUs. To evaluate how much gas consumption has changed, I compared 2009 consumption to that of 2010. Because of the way the gas company (Enbridge) does it's billing, this is not an easy task because of 2 problems:

1) They estimate my meter reading every other month

2) They don't take the reading on the same day of the month (nor on the same day of the month year to year)

As such, I decided to take 2 months consumption at a time when both months were Actual meter readings, calculate the total gas used in those 2 months, and then calculate the number of days in the 2 billing periods. I then divided the gas used by the number of days to come up with the average number of cubic meters used per day.

For 2009 (with the tank)

1) Between May and July the average consumption was: 1.984 m3/day

2) Between July and September the average consumption was: 1.84 m3/day

3) Between September and November the average consumption was: 1.91 m3/day

This consumption is fairly consistent - and we use the warmer months so as not to include home heating (actually, my furnace is only used as a backup anyway, so the data through the winter months is probably quite consistent). Perhaps the consumption is slightly higher in May/June and Sept/Nov periods because the incoming water temperature is colder.

For 2010 (with the tankless Navien NR240A)

1) Between June and August, the average consumption was: 0.952 m3/day

So how much does this translate into for cost savings? So far, (I'll provide the math/data later once a bit more data has come in), it's saved an average of $12.38 per month, which would work out to about $148.56 per year. (Notes: to be accurate, we should reduce these savings by the amount our power bill goes up (about 50 cents per month)). So let's call the savings $148.56 - (12 * .50) = $142.56 per year.

Chart (to be updated over time)