How can one determine when a dual-fuel HVAC system is the right?
Given all the refrigerant leaks Ive seen over many, many years I really wouldnt like the idea of highly flammable gas in the same cabinet as a fossil fuel burner. Its like smoking a cigarette at a gas pump - but thats just me. Dual fuel is really a misnomer taken from generators that can run on gasoline or natural gas/propane. A heat pump/gas furnace is just not dual fuel - heat pump has no combustion/fuel. The dual fuel systems I see are simply standard efficiency gas fired heaters with a heat pump A coil on top with an outside air/air heat pump - big wup - theyve been around since the 1980s. Now if you can find a ground source geothermal heat pump (COP at least 4.5) with a condensing gas furnace with ducted intake and exhaust unit as supplemental heat and a full economizer, Id be interested (BTW the combustion chamber is sealed off from the room. An air/air heat pump efficiency drops off rapidly below 32 degrees so the system relies on supplemental heat - gas furnace or resistance. Now a standard gas , or any fuel furnace needs lots of air and there usually no outside ventilation to basements - it would get freaken cold and freeze all the pipes. So the furnace relies on air infiltration - sucking cold air into the house to replace the nice warm air your furnace is using to heat your house - kinda dumb if you ask me. A condensing furnace eliminates that. A ground source heat pump is always operating with condenser or evaporator water temperature of 55 F minimum so the COP remains constant - at maximum efficiency. The only requirement is underground water within 75 feet or a backyard 100 x 150 to bury the pipe grid 4 down (approx). No need for any supplementary heat up to around 50 degree latitude - resistance heat if for emergency only. In fact you can add a desuperheater and get most of your hot water free