Undersized Baseboard Radiation?

Discussion in 'HVAC Heating & Cooling' started by billmarc, Jan 7, 2008.

  1. billmarc

    billmarc New Member

    Jan 4, 2008
    My house has a 5 zone hydronic heating system. One of the zones is slow to warm up when I set the thermostat up, and never gets up to temperature when the outside temp is below 20F. I have insulated the supply and return lines to the zone and bled the lines to remove all air. I think that the problem is just too little radiator for the heat loss.

    Is there a straight forward way of calculating baseboard radiation required for a room?

    P.S. House was built in 1989; this is our first winter in the home, so don't know if this is a new problem, but suspect not.
  2. therinnaiguy

    therinnaiguy New Member

    Jan 3, 2008
    Not Enough?

    Check with the manufacturer of your baseboard. They will be able to tell you how many Btu's per foot it will put out at a certain temperature of water. For example, typically you will get 580 Btu's per foot at 180 degree boiler water with Sterling standard baseboard. Calculate your room area in square feet. Typically you will need 20 Btu's per square foot so a 12x20 area (240 sq.ft.) needs 4,800 Btus. Or 8.25 feet of baseboard. Areas of the world do figure it differently so check with a local heating contractor in your area for exact calculations.

    You can always bump up your boiler water temperature to see if it can accomidate your heating needs or you may have a valve that is restricting the water going into the baseboard. :eek:
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  4. BigLou

    BigLou New Member

    Nov 7, 2007
    No there is no easy way to do it, every house is different and every baseboard convector will have a different rating.

    Undersizing is always a possibility however I have yet to see a house with undersized heating

  5. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    I have seen a some things that affect the heating, but first you should find out whether the problem is inadequate convection or inadequate heat supply.

    You can tell if the problem is caused by not enough heating from the circulating water by the following procedure:

    Put a thermometer (you can try using a meat thermometer but that is not very sensitive) against the incoming pipe, with the sensor and pipe well covered so the air doesn't cool them. Measure the temperature of the pipe. Do it on the incoming and outgoing ends of the unit. Compare with a unit that provides adequate heat. If the offending unit is hotter at the outlet pipe than others in the system, then the convection from the unit is inadequate.

    If the outgoing pipe is colder than others that are working then you are not getting enough hot water to the unit.

    If you have a multispeed circulator, turn up the speed to the maximum.

    Check the orientation of the fins. Most have a closed portion where adjacent fins have no space between them, and an open portion. They should be installed so the spaces are oriented to allow vertical air-flow through the fins.

    One installation that I saw had thick-pile carpet that came up against the bottom of the unit in such a way that it restricted circulation of air over the fins. There was plenty of heat when the carpet was trimmed back and nailed down.

    If you have furniture or curtains that come down to the unit, that will restrict air flow and reduce heating. If it is under a window, close the curtains to prevent the rising warm air from passing directly against the glass.

    Sometimes there is a damper that controls convection of air over the fins. You could get a little improvement by completely removing the damper. They usually pop off a bracket with a little force, and can be reinstalled.
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