Hydro Air or Furnace

Seth_7

I am seeking to improve the efficiency of an existing hydro-air system. The system has a high limit gas boiler, 180,000 IBR BTUs, feeding three air handlers with coils and three kick heaters in the two bathrooms and entryway to prevent them from freezing. The building is a church and unoccupied most of the time. It has programmable thermostates that bring the building from 60 F when the building is unoccupied to 71 F when it is occupied. The system has an outside air preheater for the air handlers. Since the cost of running the system is very high, I'd like to install the most efficient system for the building. I am able to install a new modulating gas boiler, an oil boiler, or put furnaces in the attic and replace the kick heaters with electic heaters. However, I am unsure which choice will guarantee the lowest operating cost (factoring inflation). Additionally, what temperature is best for the unoccupied building?

Steamhead (in transit)

First, do a heat-loss calculation

that BTU output sounds a bit low for a church of any size. You might find the problem there.

I'd still stay with hydro-air if you can't use some sort of direct hydronic system such as baseboard or radiant. The typical duct system loses something like 20% of what goes into it, which isn't chump change these days.

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tim smith

Church heat

I would also stay with water to air, condensing boiler good option. Also make sure their are dampers on fresh air intakes for building. Left closed during set back times when no occupancy so your not having to heat outside air when no one there and no need for fresh air makeup just to maintain minimum temp in bldg. Min temp requirements vary, if you have a pipe organ then the less temp swing it sees the better. If not, I would say probably 55 degrees is a good #, although you will get some movement of wood items in structure which can cause some separation of joints. Tim