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Heat pump vs. Gas Furnaces in tight houses

As you add insulation to a home and tighten up the building envelope, the heating load drops much faster than the cooling load. This makes sense because the winter delta-T (temperature difference between inside and out) is much greater, and infiltration rates are typically higher.

This creates a dilemma when sizing a furnace. The furnace must be sized to handle the cooling CFM even if that means selecting a model with several times more heating capacity than the load. In hot climates such as Austin Texas, it's not unusual to see furnaces oversized by 300%, 400%, or even more. 

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In warm climates with average or better electric rates, the heat pump is hands-down the best heating system. It costs less to operate than a furnace (most markets), and in tight, well insulated homes, a heat pump is actually more comfortable. The lower supply temperature, once considered the bane of heat pumps, is actually preferable in well insulated homes.

Most modern inverter driven heat pumps can operate down to 5 degrees without loosing capacity making them the perfect fit for a spray foam well insulated home.