Appendix - All About Gas Fireplaces
Determining How a Gas Fireplace Will Affect Your Heating Bill

Step 1: Determine the price of different energy sources in your area

Call your local electric utility or natural gas, propane or oil dealer to determine the cost of energy sources in your area. Be sure to get the prices for the energy sources in the same units as used in Table 1. Write the costs in the spaces provided. (Information from Table 1 will be used in Step 4 to calculate your home's annual heating costs.) If your local gas price is given in gigajoules (GJ), you can convert it to cubic metres (m3) by multiplying the price per gigajoule by 0.0375. For example:

$5.17/GJ x 0.0375 = $0.19/m³

Table 1. Energy Content and Local Price of Various Energy Sources

Conversion 1000 MJ = 1 GJ   1 MJ =947.82 Btu
* The figures provided for wood are for a “full ”cord, measuring
1.2 m x 1.2 m x 2.4 m (4 ft. x 4 ft. x 8 ft. ).

megajoules (MJ)
metres (m)
litres (L)
feet (ft)
kilowatt-hours (kWh)
gigajoule (GJ)
Britiish thermal units (Btu)

Step 2: Find the seasonal efficiency of your existing central heating system in Table 2.

Table 2.Typical Heating System Efficiencies

*COP =Coefficient of performance,a measure of the heat delivered by a heat pump over the heating season per unit of electricity consumed.

Step 3: Determine your home's annual heating load

If you know your bill for space heating and the unit cost of your energy source, you can determine your annual heating load in gigajoules (GJ) from the following equation:

For example, suppose you have been able to determine that your annual space heating bill with natural gas is $687, and gas costs $0.22 per m³, and you have an old conventional gas furnace with a seasonal efficiency of 60 percent (from Table 2). From Table 1, energy content of natural gas is 37.5 MJ/m³.

If your bills also include tap water heating and even equipment rentals, you still can calculate your annual heating load, but it will require a little more care and calculation to separate out your heating portion.

If you can't consult your heating bills, you can estimate your annual heating load in GJ from Table 3, selecting the house type and location that is closest to your own.

Table 3. Typical Annual Heating Loads in Gigajoules (GJ) for Various Housing Types in Canadian Cities

Note: “New ”means houses built in 1990 or later, and “old ”means houses built before 1990. Due to construction practices, “weatherizing ” and re-insulating (which can be different from house to house) , these figures are meant to be used only as general guidelines; they should not substitute for an accurate heating requirement determination.

Assumptions:
New townhouse – inside unit,approximately 93 m 2 (1000 sq.ft.)
New semi-detached – approximately 139 m 2 (1500 sq.ft.)
New detached – approximately 186 m 2 (2000 sq.ft.)
Old detached – approximately 186 m 2 (2000 sq.ft.)

Step 4: Use the following equation to estimate heating costs

Once you know the heating load and local energy prices, your home 's annual heating costs can be calculated using the following equation:

Step 5: Choose the fireplaces you wish to evaluate

Determine which gas fireplaces you are interested in and obtain their EnerGuide fireplace efficiencies.

Example 1

Assume you have a 12-year-old house that is heated with electric baseboards and you intend to install a gas fireplace to reduce your electricity bills. You have chosen to locate the fireplace in a major living area where its heat will reach other parts of the house.

Your choices are a direct-vent fireplace with 72% efficiency and a natural gas fireplace with 30% efficiency or a similar propane fireplace that operates at 72% or 30% efficiency. Local energy costs are $0.20/m³ for natural gas, $0.33/L for propane and $0.08/kWh for electricity. If your house heating load is 100 GJ per year and you would like to displace 40% of that load with the gas fireplace, what would your costs be relative to the existing electric heat?

Using the formula

(see Table 1 on page 30 for energy content values)

The total cost to heat the house electrically at 100% efficiency is

You wish to displace 40%of the total heat load of 100 GJ,or 40 GJ (40%÷100%x100 GJ =40 GJ).

The cost to heat this portion electrically at 100% efficiency is

The cost to heat this portion with an efficient (72%) natural gas fireplace is

The cost to heat this portion with an inefficient (30%) natural gas fireplace is

The cost to heat this portion with an efficient (72%) propane fireplace is

The cost to heat this portion with an inefficient (30%) propane fireplace is

Thus with the efficient direct-vent natural gas fireplace, you could reduce your overall heating costs by as much as $593/year ($889 –$296), or 27% of your current electric heating bill.

With the inefficient natural gas fireplace, your heating costs would still be reduced by $178/year ($889 –$711), or 8% of your total heating bill.

With the efficient direct-vent propane fireplace, your heating costs would be reduced by $164/year ($889 –$725), or 7% of your total heating bill.

By installing the inefficient propane fireplace, your heating costs could be increased by $850 ($889 – $1739), or 38% of your total heating bill.

Based on the above calculations, the direct-vent natural gas fireplace with 72% efficiency (when properly located in the house) appears to be an effective way to lower your overall heating costs while providing comfort and aesthetic pleasure.

Table A1. Summary of Calculations from
Example 1

Example 2

Assume you have a small, 25-year-old house heated by a conventional oil furnace and burner and that your oil heating bill for one year is $870. According to Table 2 on page 31, the seasonal efficiency of this type of oil furnace is 60%. You are considering purchasing a propane fireplace with a seasonal efficiency of 55%. With oil costing $0.35/L and propane costing $0.33/L, what would be the impact on your heating bill if you wanted to displace 20% of oil heating using a fireplace?

First, calculate the amount of oil used during the heating season. To do this, divide the cost of oil per year by the cost per litre, as follows:

Then, calculate your home's total heating load using the following equation:

For the purposes of this example, the result is as follows:

The amount of heat to be supplied by the propane fireplace is 20% of 57 GJ, or 11.4 GJ.

Now, using the equation for determining a home's heating cost

calculate how much it will cost to provide 20% of the heating load using a propane fireplace with 55% efficiency:

Since 20% of your current $870 oil heating bill amounts to only $174, it would actually cost you an additional $96 ($270 – $174) per year to displace 20% of your oil heat with the propane fireplace – hardly an incentive for proceeding with the purchase!

Table A2. Summary of Calculations from
Example 2

Example 3

Assume you have an eight-year-old house heated by a conventional natural gas furnace that is 60% efficient. You want to install a natural gas fireplace that is 70% efficient. Your total heating load is 80 GJ, and the cost for natural gas in your area is $0.21 per m³. What would be the impact on your heating bill if you displaced 25% of your central furnace heating with the fireplace?

Using the equation for calculating total heating costs, we learn that it costs $747 to heat your home using the natural gas furnace:

The amount of heat you want to supply using the fireplace is 25% of 80 GJ, or 20 GJ. The cost of providing this amount of heat with a natural gas fireplace that is 70% efficient is as follows:

Since 25% of your current gas heating bill amounts to $187, you could reduce your gas bill by $27 ($187 – $160) per year by installing a natural gas fireplace that is 70% efficient.

Table A3. Summary of Calculations from
Example 3

Source: Natural Resources Canada (NRCan) - Office of Energy Efficienc

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