> A natural gas furnace requires ~150cfm airflow per 10kbtu heat produced, while a heat pump requires 330cfm per 10kbtu.
How do you arrive at these figures? First, you are stating flow numbers at total energy which does not make sense. Second, airflow requirements at certain power (not energy you cite) come from heat exchanger size and temperature gradient. What are operational parameters of the reference natgas heater?
Let's assume that you mean 10kbtu/h instead of 10kbtu. That is ~3kW. For reference Nibe F730 produces ~5kW at 250M^3/h, i.e. 150 cfm.
Heat pump output temp is lower than a furnace's. Thus, it needs to move more air to inject the same heating power.
In Europe, where the traditional working fluid is usually water in water radiators, this has been a big issue in popularizing heat pumps. Radiators sized right for hot water from electric or gas furnaces were undersized for heat pumps and their lower output temp. This required expensive replacing of the water network and radiators.
Heat pumps in new builds are popular for heated floors, which are great.
How do you arrive at these figures? First, you are stating flow numbers at total energy which does not make sense. Second, airflow requirements at certain power (not energy you cite) come from heat exchanger size and temperature gradient. What are operational parameters of the reference natgas heater?
Let's assume that you mean 10kbtu/h instead of 10kbtu. That is ~3kW. For reference Nibe F730 produces ~5kW at 250M^3/h, i.e. 150 cfm.