Furnace & Air Conditioner Size For 2-Story Home

A furnace or an air conditioner for your 2-story home represents a significant investment and this makes it important to buy systems of the right size. Not only will it work more efficiently, but will be able to maintain a comfortable indoor atmosphere. It’s crucial to keep in view that if an air conditioner is too large, it will use an excess amount of electricity and the air in your house will also feel too cold and clammy. On the other hand, if the air conditioner is too small, it won’t be able to keep your indoor temperatures at comfortable levels. If you want to choose the right size of air-conditioning system, you’d have to follow some basic math.

Aspects to consider

Regardless of the number of stories your home has, the air conditioner or furnace size would be dependent on the total square footage that has to be cooled. A number of other factors also come into play when estimating the size of either a furnace or AC system, such as:

    • The amount of exposure to the sun & the outdoor air
    • Type of outer wall insulation
    • Thickness of the insulation
    • The type, size & number of exterior doors and windows
    • Ceiling height
    • Other


  • Effects of undersizing or oversizing your furnace or air conditioner

    As mentioned earlier, oversizing or undersizing can impact the efficiency and performance of the system and will affect the comfort levels in your home, regardless of whether you are getting a furnace or an AC installed. Undersizing results in the system being unable to meet the required temperature settings. Aside from the comfort aspect, when you undersize your AC or furnace system, that can most likely lead to a premature failure of the units.

  • Most people are also under the misconception that larger units will also be more efficient and provide more cooling; but as discussed at the outset, this is a misconception. When we talk about the heating ability of a furnace or the cooling ability of an air conditioning unit, uniform distribution is of utmost importance and that becomes the optimum operational time of the system. When you opt for oversized units, they may be able to cool your home much quicker, but it won’t run for the optimum length of that cycle and will not provide a uniform temperature in your 2-story home. This means you will notice that there are cold and hot spots across your home.
  • When you use an oversized furnace that can cause the system to get stressed and overheated. The ducting network that exists on your property would be unable to support the large air flow volume, which will result in a pressure buildup within the return air duct and cause the furnace to overheat. In addition to erratic air distribution, when you oversize your air conditioner that results in higher humidity levels in your home. Air-conditioners are meant to dehumidify the air as well as cool the indoor spaces. The indoor evaporator coil removes water vapor and moisture from the air that’s passing through. If your property has an oversized air-conditioner, it will cycle faster and won’t be effective in dehumidifying the air to the right levels. The other factor to keep in view is the energy-efficiency of the system.
  • The furnace or the air conditioner can provide optimal efficiency only when it has been sized correctly. When you either oversize or undersize your furnace or air conditioner, it impacts the energy-efficiency and you will be saddled with higher utility bills.
  • One Unit or Two?

    This is one more question you should be asking yourself. If you live in a 2-story home, a single Ac unit might not be able to cut it. If you set the thermostat to a lower temperature to offset the warming that occurs naturally in the living spaces on the upper stories, that can cause the lower floors to become chilly and vice versa. The best way to solve the problem is to install 2 separate units, each dedicated to one level. While you do end up paying a higher upfront cost as well as operating and maintenance costs, you would be able to control the cooling or heating on the different levels more effectively. These 2 smaller units will perform the job of a single larger unit, but in a more effective way.

    The additional cost of the 2nd unit may easily be offset by sizeable energy savings in the long term. A lot of this depends on how the structure of your house is and the manner in which you use your air-conditioners. There is another distinct advantage to getting 2 units installed in your two-story home. In case there is a downtime on one system, you might just be able to maintain a certain level of cooling in the house till the time you get the dysfunctional one fixed.

    Install A Good Zoning System

    If you prefer to install a single AC system, you should consider zoning. When you divide the system into various zones that have individual thermostats, it adds to the cooling or heating capacity of the unit. The motorized dampers within the ductwork respond to the signals from the system’s central controller to direct the cool air to one zone when it reaches the temperature set on that specific thermostat.

    It will simultaneously decrease/shut down the air-flow to another zone which doesn’t need that level of cooling. A zone dampener opens and closes independent of other similar systems that are installed on the property. This allows a single AC to effectively maintain the temperature in the lower and upper floors. You have the option to turn off the cooling or heating zone on one story while the system heats only the zone/s that is being using. This functionality also makes a zoned furnace or AC system extremely cost-efficient.

    As you can see, there are a number of variables that come into the picture when you are purchasing a furnace or air conditioner for your 2-story home. This means you would have to hire the services of a professional installer to estimate what type of system would work best for your needs.