Navien Hydro Furnaces

Condensing hydro furnaces from Navien: 14,000 to 100,000 BTU, in upflow and horizontal cabinets, for natural gas or propane.

A hydro furnace heats the air through water. Instead of a flame-heated exchanger sitting in the airstream, a condensing burner heats water and a coil inside the cabinet hands that heat to the duct air. The practical consequence is that the combustion side and the air side are separate systems — a cracked-exchanger failure does not put flue gas into the supply air the way it can in a conventional furnace.

Modulation is the number worth comparing. The 14,000 to 100,000 BTU unit covers a little over a 7:1 range and the NPF700-060U3BH covers 9,000 to 60,000. A furnace that can drop to low fire runs long and gentle on a mild day instead of short-cycling, and that is where both comfort and seasonal efficiency come from — not from the peak rating.

Upflow or horizontal is the cabinet, and it decides the install. Upflow discharges out the top, for a basement or a mechanical closet ducted upward. Horizontal lies on its side for an attic or a crawlspace. Pick the orientation the space actually allows before anything else.

Condensing means a drain and new venting. A condensing appliance pulls flue gas below its dew point, so it produces acidic condensate the whole time it fires. Plan a condensate drain and a neutralizer where the receiving pipe or the local code calls for one. It also needs sealed venting sized for a condensing unit — the existing flue from an atmospheric furnace is not reusable.

Navien hydro furnace questions

Is a hydro furnace worth it? It earns its price where modulation and a sealed combustion side matter: a tight house with a wide swing between the design day and mild days, or an owner who wants flue gas kept physically away from the supply air. For a basic single-stage replacement in a mild climate, a conventional condensing furnace costs less.

What does the price include? The furnace itself. Venting, the condensate neutralizer, a cooling coil if you add air conditioning, and the thermostat are separate items, and the vent is sized to the model and the run length in Navien's installation manual.

Which size do I need? The NPF700-060U3BH (9,000–60,000 BTU, upflow) suits smaller homes and tight envelopes. The NPF700-100U5CH (upflow) and NPF700-100H5CH (horizontal) cover 14,000–100,000 BTU. Size from a Manual J load calculation, not from the old furnace's nameplate: oversizing throws away the low-fire range you are paying for.

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