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Hydronic Duct Heater

Brad White
Brad White Member Posts: 2,398
If you have the hydronic capacity as you say, an in-duct coil is simple to do using circulator control. However, I would install an intermediate heat exchanger, either a plate type or a small indirect with glycol on the load side.

The indirect is my preference because it will act as a buffer tank in the bargain and save some cycling.

Your in-duct coil should be at least two rows, maybe four, to allow use with low water temperatures. If you size the coil for slightly less than your radiant temperature the coil may well be four rows and larger in face area.

If you size the coil for any warmer water temperature (assuming the rest of the house is radiant) the HEX will govern your entire system temperature and your radiant side may need a mixing device.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad


  • Frank M
    Frank M Member Posts: 3
    Hydronic Duct Heater


    I've got radiant in-floor and love it, but need to bring in fresh air. And I'd like to heat it, instead of dumping dead-of-winter 50 degree air into the house. A whole house ventilation system is in place but the heat recovery portion doesn't help much at low temperatures.

    So "all" I need to do is add a heater. I've got a Trinity on the wall and plenty of capacity. My plumber will do the hydronic installation.

    I'm only looking at 200 cfm, so I'm concerned that a simple core and thermostat would short-cycle, unless the water is dialed way down. But of course it there will always be the day when it hits the ugly zone.

    Is there a self-contained Modulating hydronic unit - core, stat, and valve - that could be dropped in here?

    Or is there a better solution?

  • Joe Brix
    Joe Brix Member Posts: 626
    I'd also look for humidification

    Maybe aprilaire has something? Bringing in dry outside air is gonna drop the overall humidity level of the house.
  • Rollie Peck
    Rollie Peck Member Posts: 47

    Hi Frank:

    I bring in outside air through an eight inch pipe that

    opens a couple of feet from my boiler in the boiler room.

    Besides supplying combustion air for the boiler and hot

    water heater, it supplies makeup air for the rest of the

    house through some openings in the boiler room walls. The

    openings are near the top of the boiler room, so the air

    going into the house is quite warm.

    Rollie Peck

  • Brad White
    Brad White Member Posts: 2,398

    Something about what you describe indicates to me that if you had a CO incident in your boiler, you could send that CO immediately to your living space (speeding up a dangerous condition).

    Is there direct communication, (ducted) between your boiler and living area?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Frank M
    Frank M Member Posts: 3

    It's unlikely CO could get into the house system. I'm using a heat recovery ventilator which has dedicated through-the-roof intake and exhaust vents, well away from the boiler vent. All ducting is sealed. IF - big IF - the ventilation system developed a gasket leak on the intake side, concident with a mechanical room CO problem, then the potential exists. Alarms will go off in the meantime.

    But, thanks for the heads up.
  • jp_2
    jp_2 Member Posts: 1,935

    are you saying your mechnical room is 100% sealed from the rest of the house?
  • Frank M
    Frank M Member Posts: 3

    The mechanical room is in the garage, separated from the rest of the house by a 6" concrete wall, with the exception of the fire-door into the house. The attic separation is framed and sheetrocked on both sides, and sealed with acoustic caulk. On the house side of the fire-door is a exhausting vent to carry garage/auto/paint/crap back outside.

    100% - probably not. But Close.

    And the fresh air I refered to in the original post is for the house, not the mechanical room. The boiler is a trinity direct vent with dedicated intake and exhaust vents.

This discussion has been closed.