Prioritized IHW Cycling
I have a Burnham Alpine 150 with a Burnham 50 gal IHW tank piped off of the secondary loop using 1" copper. The tank has priority. My question is should I be tweaking the max fan speed on calls for hot water so that the boiler only cycles once for as long as needed each time the tank calls for hot water? Or is this a moving target? The boiler doesn't cycle more than once every time the tank calls for water, but it does happen sometimes.
The max fan speed on the boiler is 5500 and I believe that the max it is set to right now for hot water calls is 4000. This number can be set independently from the max fan speed when heating zones are calling for heat.
It probably doesn't much matter if the minimum burn time during hot water calls is at least a couple of minutes. If the boiler is only getting ahead of the heat exchanger once in awhile it's not a big deal. If it were happening often or every time, it's worth dialing back the flow or taking other measures on the primary side to prevent it.
If it's simply a matter of punching in a number into the setup on this boiler, go ahead. As long as you're not running out of hot water, the lower the firing rate the better. Running the boiler at a lower fire modestly improves the combustion efficiency of a mod con.