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Air handler or fan coil for low load home?

user-6603341 | Posted in Mechanicals on


I am building a 2,000 sq.ft. townhouse in Oakland, CA. I plan to use a Sanden heat pump hot water heater to provide both domestic hot water and space heating. I am seeking guidance on how best to distribute the heat to the basement, first floor, second floor, and attic loft. Due to budgetary constraints, I am looking for the most economical heating distribution system. While a hydronic distribution system would be nice, I assume forced air is going to be my best bet – let me know if you disagree!

We hired energy vanguard to perform a heat load (there will be no cooling). The home will have a heat load of 15,000 btuh, which equates to needing an air handler or fan coil that can move 600 cfm of air.

I have two questions (for now):
– What is the best approach when designing a forced air distribution system for a low load home?
– Does anyone know of an air handler or fan coil make/model that would be ideal for this application?

Thanks in advance for your thoughts!

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  1. GBA Editor
    Martin Holladay | | #1

    There are a couple of issues here.

    1. The first issue is, do you want air conditioning? The Sanden does not produce chilled water. If you want air conditioning, you'll probably want some type of forced-air ductwork -- unless you will be cooling with ductless minisplits, in which case I would advise you to skip the idea of using the Sanden, and instead just using the ductless minisplits for heating as well as cooling.

    2. The second issue concerns the water temperature of your system. Remember that best temperature for domestic hot water is lower than the usual design temperature for hydronic systems, and that most air handlers used for hydro-air systems have heat-exchange coils that are designed for relatively high water temperatures.

    In short, you need an experienced engineer to design this system.

    I advise you to read two articles:

    Air-to-Water Heat Pumps

    Using a Tankless Water Heater for Space Heat

    Here is an excerpt from the second of the two articles listed above: “As building scientist John Straube explained, 'You need to choose a low-watt blower and a low-watt pump. This requires design. That means it’s harder to get these systems into the mass market.' Like Magande, Straube advises that these systems work best if the flow rate to the space heating coil is under 2 gallons per minute.”

    If you end up with a hydro-air system, you'll probably want an air handler from First Company.

    -- Martin Holladay

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