How to Size Your HVAC and Water Heater to Fit Your Home

Updated: Jan. 04, 2023

Building a home? Here are some tips to help you figure out what kind of HVAC system and water heater you'll need.

American Standard HVAC SystemFamily Handyman

Get the Size Right

  • When sized correctly for your home, your furnace and water heater will provide a long life of efficient service.
  • When building our Getaway home project, we estimated our British Thermal Unit (BTU) requirements for our furnace by multiplying our square footage by the heating factor for our zone (40 to 50 BTUs per square foot). Working with a technician from American Standard Air, we made sure the furnace we chose was perfectly sized for the structure.

Save Propane with Dual-Fuel

  • The Getaway was not designed as a year-round home. We won’t live here full time, so we don’t want to heat it full time.
  • We chose a high-efficiency, dual-fuel furnace to reduce our yearly propane usage. We’ll use it only in the deep cold months. In early spring and late fall, we can use electricity.

American Standard Platinum 20 Heat PumpFamily Handyman

Breathe Easy

American Standard Whole Home Air CleanerFamily Handyman

  • Our HVAC system makes the most of the fresh air around us. By air balancing, every room in a house can receive the right amount of conditioned air.
  • The air exchanger enhances the efficiency of the system by removing stale air and replacing it with outdoor air.
  • The American Standard whole-home air filter removes allergens and dust and maximizes the quality of the air inside.

Never Wait for Hot Water

Navien NPE-240s2 Water HeaterFamily Handyman

  • When we arrive at our Getaway late on a Friday night after hours of driving, we don’t want to wait for hot water.
  • That’s why we went with an on-demand water heater, which eliminates the big water tank (and the cost of keeping all that water hot). More importantly, it delivers hot water instantly.

Balance Size With Demand

  • Sizing a tankless water heater involves a tricky balance.
  • Factors we considered were maximum demand in gpm (gallons per minute), the incoming water temperature and the desired hot water temperature.
  • Joel Myers from My Plumbers, LLC helped us determine that six gpm is our maximum possible hot water demand.
  • Groundwater in this zone is 45 F, and we want our hot water to be 115 F. To accommodate a 70-degree rise at six gpm, we chose the gas-powered Navien NPE-240S2-NG.

Well Water Challenges

  • When fed by well water, a tankless water heater needs a good filter.
  • Sediment will clog the heating elements. Lime scale buildup can also be a big problem.
  • We had two possible solutions: Place a filter between the well and the water heater, or plan to routinely flush our system.
  • We chose to put in a filter so maintenance would be easier.