Figure 1 shows a piping layout that was used to retrofit a pellet-fired boiler to an existing 4-zone heating system supplied by an oil-fired boiler. The pellet boiler is protected against sustained flue gas condensation by a “loading unit,” which combines a circulator with a thermostatic mixing valve. The distribution system is connected to the retrofitted pellet boiler piping using a pair of closely spaced tees. Can you spot several errors in this piping layout and propose modifications that would correct them?