Where’s the balance and how do we make the best choice between a heat pump only or a dual fuel system? Here we explore several of the usual scenarios to help you decide.
Product Life, Comfort and Emissions
Product life cycle analysis tells us not to throw things away until they are no longer useful. A recently installed two stage furnace has lots of life left and holds huge sunk costs for budget and environment.
On the other hand, emissions draw down as fast as possible is driving the minds of change makers and innovators. They are definitely are watching the climate health numbers closely.
Dual fuel systems offer comfort and backup. But there’s more to the story, especially if you’re thinking bigger picture. That big picture connects your furnace to the grid and the planet.
Electricity and Gas “Emergency Heat”
Is a gas furnace a reliable emergency heat source? Yes, if your electricity is ON. But, if your electricity is OFF, then no, your forced air gas furnace is not going to heat in that type of emergency.
By nearly any measure, emergency heat is a good idea, especially during a winter blackout. Think wood, kerosene or pellets. But electricity is needed to run any heat pump AND any forced air furnace. So, these “emergency heat” systems will not work in a power outage.
If gas furnaces won’t run without electricity, so why have it at all? Well insulated homes in the coldest parts of Colorado have run on one heat pump only all winter with no back up or supplemental heat, and no temperature problems or very high power draw. So, why add gas? Or, rather why keep gas AND add a heat pump?
A typical dual fuel system in this context is the heat pump plus gas furnace design. Technically, electricity is not a fuel. However, “dual fuel” assumes so in the HVAC community for simplicity and marketing. Chemical or electromagnetic. Is electricity a fuel? No and yes. Just roll with it.
Dual Fuel = Heat Pump + Gas Furnace
Indeed, there are situations which help your decision either way. Let’s first explore reasons a dual fuel system makes good sense.
Reason YES #1 – You Have A Newer Furnace
Dual fuel makes sense when your furnace is young, and has a long life of service ahead. All the mined and refined metals, pumps, motors and manufacturing as well as the cost and installation are major considerations.
In commerce, life cycle analysis is used to measure if a product is well utilized. For a heat pump, a furnace or any appliance, the costs and benefits to your wallet, your home and the planet all come into the equation. If your furnace is less than 10 years old, a dual fuel system may be the right choice.
Reason YES #2 – You Have A Cold House
Many homes just run cold. This may be due to poor insulation, modular construction, leaky windows and many more situations. If totally upgrading your home’s energy efficiency envelope is too costly, time consuming or not an option, dual fuel can make sense.
For the poorly insulated home, a heat pump can meet upwards of 90% of the heating needs, just activating the furnace heat on the very cold deep winter days and nights. Energy and climate savings are mostly still realized, and the home stays comfortable year round.
Reason YES #3 – You Have Coal and Gas Based Power
If your power provider burns lots of fuels to generate electricity, dual fuel home heating makes more sense. This is especially true when electricity demand spikes in winter and summer during the coldest and hottest times of day.
As electricity demand increases, power companies meet that demand with increased fuel burn rates to push more electrons onto the grid. This increased demand increases the rate of emissions for electricity.
Switching from electricity to gas during peak cold climate winter demands, can, depending on the grid’s power generation technologies, make sense to actually reduce emissions. Amazing but true.
Now, let’s flip our view and look at reasons to avoid a dual fuel system.
Reason NO #1 – You’re Building A New Home
Dual Fuel systems don’t make sense in new home builds. A good design for the home and heat pump is all that is needed. Usually, the gas infrastructure is added cost that meets the tastes and preferences of either the homeowner or builder.
In a right sized and well designed heat pump system, the home heating and cooling needs are met.
Sidenote – I’m personally a big fan of having emergency heat, the kind that runs without power. If you’re in the design phase, a fireplace is an option that one day could be a lifesaver.
Reason NO #2 – You Have An Old Furnace
Dual Fuel systems don’t make sense for most old furnace replacements. Sizing the heat pump to meet the home heating needs is essential, but gas back up heat is not.
Summary
In some cases your home comfort and budget can benefit from a dual fuel heat pump system. If your furnace is young, home isn’t getting insulation upgrades, or your grid is powered by mostly gas and coal, then a heat pump with gas back up furnace could make sense.
In many cases, your home comfort and budget are best served with only a heat pump, not dual fuel. If your furnace is old, your home fairly well insulated, and your grid is on track with low emissions goals, then getting a right sized heat pump install is your best option.
More questions on dual fuel heat pump design considerations? Contact us to learn more.
