There are several calculations that the HVAC technician needs to do in order to ensure that the furnace they install in your home is the correct size. That means that you should make any changes that can affect this calculation before the technician does the calculation.
Install Additional Insulation and Fix Any Leaks
Part of the calculation that determines what furnace size you need is how airtight your home is. New homes are completely sealed, but older ones were designed to breathe. While it does improve the air quality, this makes your HVAC system horribly inefficient. Worse, many duct systems are poorly installed or have leaks, resulting in large amounts of wasted energy. Fixing these problems will allow you to get the same effect with a smaller furnace.
Talk to the Contractor About Adding Additional Filtration
With your newly sealed home, indoor air quality is going to need your attention. Your furnace fan can only push so much air through the system, which limits what kind of filter you can add. If you want to put in a high end filter system, you should let your technician know. That way they can ensure the furnace they install can handle the additional load.
Talk About Any System Changes You Want to Make
It is rare to change the type of heating system you use as part of a replacement because it often requires digging into the walls, but you can do it. If you want to change your energy source or move to a different type of heating system, you should talk to your contractor about it. Their experience will help you discover what the actual cost of this change will be before you make the final decision.
Ensure That Your Contractor Actually Does the Appropriate Calculations
Unfortunately, many contractors don't take the time to do all the calculations. They will simply take your square footage and maybe the local climate into consideration. Have them walk you through the calculation so you can be sure that they have included your insulation, family size, and filters into account when recommending a product. Poorly sized furnaces not only cost you more in your monthly bills, they do not live as long. Many contractors install a bigger unit just "to be safe," but this isn't something that you should accept as an explanation.
Having your furnace installed properly by a company like Ice Age Mechanical ensures that you will minimize your energy bills for the next decade. Ensuring that all the correct information is given to your technician will give you the best possible chance of getting the right sized furnace.