I recently decided to have a look at my costs for heating my home and hot water. I was hoping to gain some insight into whether or not I should upgrade my heater or hot water tank to a higher efficiency model.
My heater and hot water tank both run on natural gas. Fortunately the gas company provides a nice little summary of past usage with each bill, giving the average daily consumption for each month over the past year. Those numbers have been entered into the following table under the heading “Daily Gas.” The numbers for “Water Gas,” which is the amount of gas used to heat hot water, were derived from the usage in the summer months, when I don’t run my heater. To get the “Heat Gas,” I simply subtracted the gas used for hot water from the total.
Here is my usage data for the last year:
| Month | Daily Gas | Month Cost | Water Gas | Heat Gas |
|---|---|---|---|---|
| January | 0.50 | $140 | 0.10 | 0.40 |
| February | 0.38 | $106 | 0.10 | 0.28 |
| March | 0.36 | $101 | 0.10 | 0.26 |
| April | 0.26 | $73 | 0.10 | 0.16 |
| May | 0.16 | $45 | 0.10 | 0.06 |
| June | 0.10 | $28 | 0.10 | 0.00 |
| July | 0.09 | $25 | 0.09 | 0.00 |
| August | 0.08 | $22 | 0.08 | 0.00 |
| September | 0.09 | $25 | 0.09 | 0.00 |
| October | 0.17 | $47 | 0.10 | 0.07 |
| November | 0.36 | $101 | 0.10 | 0.26 |
| December | 0.42 | $117 | 0.10 | 0.32 |
| Total: | 89.1 | $830 | 34.8 | 54.3 |
Note: the gas usage numbers are in GJ/day. For the totals we multiply by 30 for each month. (Not all months have 30 days, but close enough.)
My current cost of gas is $7.379/GJ + carbon tax of $1.49/GJ + 5% GST for a total of $9.31/GJ.
HOT WATER TANK
My installed hot water tank is a standard atmospheric vent type, which is typically about 60% efficient. Upgrade options include a power vented tank, with about 70% efficiency, a tankless system with about 81% efficiency, or a tankless condensing system, with 95% efficiency. The following table shows the expected yearly operating savings after an upgrade.
| HOT WATER HEATER TYPE | EFF. | YEAR COST | SAVINGS |
|---|---|---|---|
| Atmospheric Vent (current) | 60% | $324 | – |
| Power Vent | 70% | $278 | $46 |
| Tankless | 81% | $240 | $84 |
| Tankless condensing | 95% | $205 | $119 |
(For future reference I measured my current water temperature differential and found it to be 118 – 54 = 64 F, or 48 – 12 = 36 C.)
FURNACE
My installed furnace is rated for 80% efficiency.
Current cost of heating home at 80% efficiency: $506
Theoretical cost if upgraded to 95% efficiency: $426
Savings per year with upgraded furnace: $80
CONCLUSIONS
As one can see, the potential savings per year are not all that substantial. When you’re paying just $830 per year for your heating costs, there’s not a lot of room there for major expenditures. (By the way, there is also a $12 per month “basic charge,” so my total costs are $974.) Yeah, the savings do add up over the years, but the higher efficiency appliances are substantially more expensive and generally have greater maintenance costs.
When my current appliances reach end of life I will definitely want to upgrade. At the current time, though, it looks like I should just stick with what I have. It would currently take far too long to recoup any investment.
I do expect carbon taxes to increase steadily over the coming years. At some point it probably will make sense to upgrade, even if my appliances do not yet need replacing.
vanTopia 