Number of taps needed in an FIR filter to remove DC An FIR filter is being used to remove the DC of an ECG. The sampling rate is 500Hz. How many taps would said FIR filter require (theoretically and practically) to filter out the DC. 

P.S. the filter would be a high-pass filter and would not remove the 1Hz fundamental frequency component of the ECG.
See How many taps does an FIR filter need?

In your case you'd need more than 1000 taps depending on the allowable ripple, as your cut-off frequency is less than fs/500.

Alternatives :


use an IIR, a simple order-1 DC removal filter could work great
Average your signal and subtract the average in order to remove the DC
Rick Lyons proposes a clever implementation of an FIR DC removal filter using cascaded-integrator-comb filters here https://www.dsprelated.com/showarticle/58.php