I wouldn't waste my time -
Recording Studio design criteria is NC 15-20 - which would translate to roughly 25-30dB, but this is also frequency dependent (lower levels at higher frequencies - higher levels at lower frequencies - for example an NC 20 would be around 51dB max at 63Hz and only 16dB max at 8kHz.
So the frequency of the equipment (which should be constant at a particular frequency) will be the real question, although units like that are generally very VERY quiet.
However - let's assume for a moment that it really was an issue for you....... it is not like your vocal recordings are going to take a continuous hour at a time -
You could (much more easily) tie the unit into a red light switch, bring the room to temperature and then just kill the unit for the few minutes you are actually tracking the vocal - no reason to worry about it during practice - or warm ups - etc.
A better question (in my mind anyway) would be how you are handling fresh air for the space? And the potential for noise issues in that regard..........