Drain water from one zone to replace section of baseboard pipe?

bd52

I've got a Slant Fin Sentinel nat gas fired boiler and a 2 zone baseboard system. As part of a room remodel, I'd like to upgrade the baseboard pipe in that room (damaged fins), and I also need to get it out of the way so I can get to the framing as well as to install new drywall. So to cut out the pipe here, I'll need to drain (some) of the water out of this zone (zone #1).

The boiler setup:


The room in question is on the ground floor. Zone 1 covers the ground floor and basement. The zone 1 return connects to the green pump. The installer seems to have done a good job in terms of installing lots of valves.

As I understand it, I'll need to perform the following steps:

1. turn off power to the boiler
   
2. close gas supply shutoff valve
   
3. turn off water supply to boiler
   
4. close off Zone 2 (the zone I do NOT wish to drain)
   
5. open drain spigot
   

For Step 3, there are a couple of spots where I can turn off water supply to the boiler:


Either the valve circled in red, or the valve circled in blue immediately before water enters the boiler. Which is preferable to use to shut off water supply in this situation where I'm draining one zone?

For Step 4, Zone 2 (the zone I'm NOT draining) is the piping connected to the black pump. Do I close the valve above or below the pump? Is that the only valve on Zone 2 that needs to be closed to prevent losing any water from that zone?


When I open the drain spigot, since the room being remodeled is on the ground floor (upper floor of Zone 1), I suppose I don't need to drain the entire zone, just enough to empty the upper floor of Zone 1. How can I ballpark how much water that would be, or is that not really important - i.e., no harm in draining most or all of Zone 1?

After I'm done draining Zone 1, should I reopen the valve I closed on Zone 2?

Assuming the room remodel will take a few weeks, should I seal off the cut open piping to minimize oxidation?

Since it's late spring/early summer, I don't need heat, so I'll just leave the boiler off during the room remodel. Any harm in leaving it off along with leaving Zone 1 partially empty for a few weeks?