The head feet isn't how high you are lifting, it is the restriction in the line. The pipe, elbows, heat exchangers, etc give some head loss. The return water in the return pipe acts as a siphon so you aren't actually lifting the water at all after the air is out even if the house is way higher.
The head pressure loss gets higher as the flow rate increases so it is hard to calculate. An average forced air heat exchanger loses about 1/2 foot at 5 gpm and about 2-1/2 feet at 10 gpm.