When installing a new HVAC system, you have a lot of decisions to make. One of the first decisions is what kind of heat to use.

First, you need to consider access. If your home doesn’t already have gas running to it, make sure you can get access to it for a reasonable price before you even consider a gas furnace.

Once you’ve determined that a gas furnace is an option, the next thing to consider is climate. Because heat pumps take heat from the outside air and move it inside, they work best in temperatures about freezing, while gas furnaces work just as well in freezing temperatures as in warmer ones.

And efficiency is the next major consideration. Since heat pumps move heat instead of burning fuel to generate it, they are significantly more energy efficient than gas furnaces. However, because natural gas is cheaper than electricity in many parts of the country, that doesn’t always immediately, translate into savings on your energy bill.

Another factor involves the other side of HVAC—air conditioning. A heat pump provides both heating and cooling, so you won’t need to buy a separate air conditioner like you would with a furnace. But because the heat pump runs all year, instead of only during the “heating season,” its lifespan will tend to be shorter than that of a furnace.

Finally, the issue of safety is always worth considering. With a gas furnace, you do have the risk of a carbon monoxide leak. Carbon monoxide poisoning can be dangerous and even fatal, so if you choose a gas furnace, it’s very important to make sure you have a working carbon monoxide alarm in your house and that you have the heat exchanger inspected annually.