Hooking up the Outdoor Furnace to an Existing Boiler
Again, we need to use a heat exchanger to transfer heat from the outdoor furnace to the
boiler or hydronic system so that the two systems remain isolated from each other. A
water-to-water plate heat exchanger is used in this type of system. No thermostat is
normally needed since we trick the boiler into thinking no heat was extracted!
The hookup is very similar to that shown above and a complete kit is available.
The 2 systems are totally isolated from each other so that the existing hydronic system
(usually pressurized) remains undisturbed and functions exactly as it did before. All
pumps and controls remain the same. The system’s return water goes through the heat
exchanger (on the right) and gets reheated before entering the existing boiler. This
tricks the boiler into thinking that no heat was extracted and it will not turn on.
The water circulates from the outdoor furnace, to the heat exchanger on the left side
(red line), out the top of the heat exchanger and back to the return (blue line) on the
outdoor furnace. Water that circulates through the furnace is never circulated through
the home’s hydronic system – or visa versa.
The 3-way valve (shown above) is not needed. Strainers are optional. The pump shown
is an existing pump (if used).
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