A multi-function pressure vessel suited for installation in a heat transfer fluid system. The multi-function pressure vessel comprises: a tank defining an internal volume, a bladder dividing the internal volume into a heat transfer fluid chamber for ac commodating expansion fluid and a pressurized gas chamber adapted to be filled with a pressurized gas. The tank has a heat transfer fluid inlet for receiving an incoming flow of heat transfer fluid from the heat transfer fluid system and a heat transfer fluid outlet connected in fluid flow communication with the heat transfer fluid inlet by an internal pipe mounted in the heat transfer fluid chamber. The internal pipe has perforations defined therein. An air vent at an upper end of the heat transfer fluid chamber is provided for venting any air bubbles passing through the perforations in the internal pipe. A drain valve may be provided at a bottom end of the heat transfer fluid chamber for removing dirt particles flowing through the perforations in the internal pipe.

A plumbing system pressure protection valve assembly that utilizes a unitary body to connect a hot water tank to a cold water supply, a vacuum breaker, and an expansion tank. The assembly includes two ball valves coupled to the unitary body to isolate the hot water tank from the cold water feed and to isolate and permit draining of the expansion tank. The assembly also includes a rod and foot coupled to a tab on the unitary body to provide support for the expansion tank service valve assembly.

In a split system heat pump cooling and heating system, an auxiliary hot water storage tank is provided as an energy storage bank. Two sets of coils run through this storage tank, a first set carrying hot refrigerant from the heat pump to deposit energy and a second set carrying hot potable water to remove energy. Valve and switch matrixes are operated at the heat pump to provide hot potable water from the energy storage bank during both normal space heating and cooling operations of the heat pump.