We replaced our natural gas furnace with a forced air electric one three years ago, after having a Lennox Pulse fail in only 13 heating seasons. Changing codes during the ensuing 13 years regarding the fresh air intake and exhausting of a new high efficiency gas furnace made converting to electric heat easier than reworking all of the existing pipes.
We haven’t changed from a gas hot water tank installed in 1999 to an electric water heater. Which of the two would be more efficient? We have the 220 wire in place for the electric heater.
This specific question has come up several times in the last few months during the course of several pre-purchase home inspections. Homebuyers are becoming much more aware of the increasing options available not only for heating systems, but also for hot water heaters. The question of efficiency of new hot water heaters should be balanced with cost of initial installation, energy cost, life expectancy and function. I will elaborate further on these topics while answering your question.
If we are talking strictly about efficiency of energy consumption, electric hot water heaters will always rate higher than natural gas, but that may not tell the whole story. The reason electric tanks are better in this regard is that virtually all the electricity consumed by the appliance for water heating is used directly for that purpose, essentially being one hundred percent efficient. This differs with hot water heat, where some of the energy is wasted due to combustion and exhaust products. Normal gas hot water heaters are between sixty and eighty percent efficient due to these factors. These figures also vary depending on the age of the units, the amount of insulation, and the hot water consumption. Because of these variables, efficiency is not necessarily the best or only consideration when deciding on changing from gas to electric.
Overall cost of installation and operation, over time, are a couple of variables to look at when making this decision, but they may be harder to quantify than efficiency. Recent charts I have seen show little cost differences between the day to day operating costs of gas vs. electric hot water heaters, but this will vary. Both hydroelectricity and natural gas costs may rise and fall during the course of a year, so average costs are the only way to measure this variation, which will be an estimate, at best. Efforts in predicting the future rates for both these sources of energy, over the normal lifespan of a water heater, may be futile. Because of this, you should concentrate on other factors when making your decision.
The first consideration, initial cost of installation, has already been partially discussed in your admission that you already have the proper wiring and circuit breaker in place for the electric unit. Normally, it is less expensive for installation of an electric hot water tank rather than gas. That is because the costs of the typical electric unit is less and installation is simpler. Natural gas appliances must be installed by a licensed gasfitter which may require modifications to the gas piping and venting when upgrades are made. Electric hot water tanks do not have these requirements, but must have the proper sized wiring and circuit breakers installed, which can be an added cost if an electrician is required for this upgrade.
The next consideration is life expectancy. Often, electric hot water heaters last longer than natural gas units due to the lack of corrosion and deterioration from the gas fired flame on the bottom of the inner tank. This does vary considerably depending on the mineral content of the water in your area. If you have private well water, there may be corrosive minerals in the water which may minimize this advantage or heavy iron concentrations that build up in the tank. If you are using nice, soft, Winnipeg municipal water, electric tanks may have a considerably longer life expectancy.
The final two items to take into concern are convenience and environmental considerations. Electric hot water heaters take longer to replenish the hot water, once depleted, than gas fired units. To compensate for this shortcoming, larger capacity tanks are normally installed, which may require more energy consumption. This additional energy use may negate the extra efficiency of electric heating, but will not affect the environmental advantages. Electric hot water heaters have no emissions and may be the choice for homeowners concerned about greenhouse gas. While natural gas is among the cleanest burning of all the fossil fuels, its use still contributes carbon to the atmosphere, while hydroelectricity does not.
To summarize, the cost of energy consumption of an electric hot water heater as apposed to a natural gas unit may be similar but other considerations should affect your decision about which to choose. Ease and cost of installation, convenience of use, and environmental concerns may be more important factors in your choice of upgrades.