Does a hydronic air handler provide greater efficiency than a highly efficient natural gas furnace?
I have not been able to find any information showing measured efficiencies of hydronic air handlers. For one, hydronic air handlers seem hard to come by (unless I’m looking in all the wrong places). The only reputable manufactures to offer them to my understanding are LifeBreath and Lennox. Neither manufacturer provides any information regarding how the efficiency of a hydronic air handler compares to a natural gas furnace or any measure of efficiency at all. A web search produces comments stating that hydronic air handlers are efficient, provide even heat, and don’t dry the air like furnaces, but no concrete data to back this up. I am looking to replace an aging furnace and water heater and want to know what would be the most efficient way to go. I am leaning towards a Navien tankless water heater that provides an EF up 0.98. It would be nice to only have one combustion appliance in the basement, but if a hydronic air handler can’t efficiently transfer heat from a water coil to the air passing through it then a 95%+ AFUE natural gas furnace may be the way to go. Thoughts?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Mike,
For one thing, it's not true that hydro-air systems "don't dry the air like furnaces." In either case, the source of the air entering the air handler is the same -- the air comes from the home's return duct. In either case, the air is warmed, either by the furnace's heat exchanger or by the hot-water coil. Neither unit adds humidity to the air stream, so either unit is equally "humidity neutral."
An air handler includes a fan. The efficiency of the air handler's fan depends on the fan's motor and the design of the air path through the unit. Furnaces also contain fans.
However, the air handler has no combustion efficiency, since the combustion occurs elsewhere. In the case of a hydro-air system, the combustion efficiency depends on the efficiency of the boiler or water heater used to heat the water.
As far as distribution efficiency is concerned, hydronic distribution (for example, using hydronic baseboard units) will be more efficient than distribution of the heat through ductwork.
If you're going to use the Navien for both heat and hot water, I would suggest using the combi made for that dual purpose.