Retrofit one-pipe monoflo tee system to a water to water WSHP.

Son taking care of dad.

Dan,

My question is how easily can I retrofit a one-pipe system to use a water-to-water heat pump?

My father is convinced his fuel oil boiler is too expensive to operate and wanted me to find a better solution. His hydronic system (installed in 1958) is a one-pipe monoflo tee single-loop application using cast-iron baseboard radiators. The challange is that I'm a HVAC professional steeped in refrigeration and air conditioning and very limited on any hydronic heating issues.

It's my opinion, that my dad's biggest problem was the size of his boiler. It's rated at 151,000 btuh -- which I thought was extremely oversized. After doing a load calculation determined he only needs about 60,000 btuh heating and slightly more than 30,000 btuh of cooling.

That said he still wants to know if he can use a watersource heatpump (WSHP) like I have. Still, my question is how easily can I retrofit his one-pipe system to include a water-to-water WSHP?

My thoughts are that if I split his loop into two that I may get by with the lower supply water temp (130 degree F max). If the lower supply temp requires more radiator surface area I wanted to include 2 or 3 12,000 btuh water fan coils that would also give him an A/C option (to get rid of his window units).

My thought was to leave the boiler plumbed in and use it as a back-up in case needed during very cold winter conditions.

Appreciate Advice,
Taking care of Dad