Can central air be installed in a 1950s home that has a floor furnace?

Asked by Norma
Wichita, KS

My brother lives on oklahoma and always used window A/C units. He installed energy saving windows this spring only to find window units no longer fit. He is now using portable air conditioning but they do not cool entire house total of 5 rooms. So he is considering central air. Is it a feasible choice?


Michael Holcomb

Answered by Michael Holcomb

Byron Center, MI

Alliance for Environmental Sustainability (Headquarters)

September 6, 2011

Great question! Not sure I have enough information to fully respond but I will try my best. You can always post a follow-up comment below if I totally missed the intent of your question.

Heat gain is the critical issue

The air conditioning load isn’t based so much on number of rooms as it is based on a heat loss/gain analysis.

  • If a home has a good thermal envelope (ceiling and wall insulation with energy efficient windows) a portable air conditioner and/or window air conditioning unit can keep a five room home very comfortable.
  • My first home was a 900 square feet ranch and we used a window shaker for years with great results.
  • A portable air conditioner can be effective as long as it is sized properly for the heat gain of the home.

Ductless air conditioning

Mitsubishi makes a variety of energy efficient, ductless air conditioning systems that would work in your brother’s home. Basically the condenser is located outdoors and one or more wall units hang in designated areas within the thermal envelop. 

  • Refrigerant is pumped to the evaporator wall unit to provide cooling (some units also provide heat) to rooms that require cooling (or heating).
  • Some models allow you to connect up to eight wall units to a single outdoor condenser.

Conventional A/C system

You also could opt to have a split coil, high pressure conventional air conditioning system installed in the home.

Basically you have a condenser outdoors and an evaporator in the attic with small diameter ducts that distribute conditioned air through ceiling grills in assorted rooms throughout the house.

Return air is brought back to the evaporator from a central location. This system is used often in larger homes with in-floor or radiant heating systems.

A recommendation and word of caution

Based on a home I suspect is under 1000 square feet the Mitsubishi ductless split system may make the most economic and performance sense for your brother.

One word of caution – make certain that an installing contractor does not install a system that is oversized for the home.

  • The only way to know what size system is required is to perform heat loss/gain calculations on the home based on room by room analysis.
  • Properly sized air conditioners will operate at peak efficiency and remove excess humidity from the air.

Good luck!

Tagged In: heating cooling

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.