I installed the 3 Ton 18 SEER ACiQ Inverter Heat Pump Condenser with a 5 ton coil that matched my furnace box. The service manual has a chart to set the pressures to based on Temperature when at stable high cool/heat. I have it setup as a dual fuel configuration with my ancient 60% furnace. I am in Iowa and we get negative Temps. This heat pump has already saved me hundreds of dollars on my heating bill.