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  1. #1
    Join Date
    Apr 2009
    Posts
    13

    Default radiant floor heat question

    We have added an addtion on to our house to expand our existing kitchen (first floor) and bedroom (2nd floor). We want to use hydronic radiant floor heat in these areas. We currently have a mix of hot water radiators and electric baseboard in the house.

    I have been soliciting estimates on our project. Today, the heating company told me that radiant floor heating can't be used alone if we want the room to be comfortable and began talking about supplemental baseboard radiators for both rooms. No one else has mentioned this.

    We keep our thermostat between 62-65 in the winter. We do have a wood stove that runs while we are home and keeps most of the present house comfortable. We don't feel that the house is too cold when we arrive home before we light the stove. We do enjoy a cost savings as the boiler does not run while once the stove gets going.

    Should I be wary of a contractor who is insisting on supplementing with baseboard radiators or by the ones who are not proposing this added feature? It was my understanding that the radiant floor heating could be used on its own.

  2. #2
    Join Date
    Feb 2008
    Posts
    554

    Default Re: radiant floor heat question

    swample:

    I would tend to agree with the contractor who recommends baseboard supplementation in your circumstance.

    Hydronic radiant floor heat is a great, economical way to heat a house, & it has become very popular for this reason in recent years---however, it operates in a slightly different manner than standard radiator/baseboard hydronic heat:

    a) rad/baseboards traditionally operate at 180 degree water temp & are sized (the length/size of the rad/baseboard) to emit heat at this temperature; radiant operates at approx. 100-120 degrees & uses the entire floor as the "radiator"---it takes much longer for the heat to build up & recede in such wooden structures so there is often slack time when the room(s) get cold until the slow response can be reversed (thus the need for baseboard)---there are outdoor reset thermostat controls that try to anticipate drops & rises in temperatures, but the system is often slow to respond.

    b) your present boiler (since it is probably not a condensing/modulating boiler) is also designed to produce hot water quickly at 180 degrees to address the output of the rads/baseboards---the output of all these components is carefully calibrated to produce a certain amount of heat in btu's/hour to make up for the escape of heat thru the walls on a cold winter's day.

    Since the contractor didn't mention replacing the boiler, I assume your present boiler is large enough to accommodate the added additions, in addition to the rest of the house---you can do your own HEAT LOSS CALCULATION and OUTPUT CALCULATIONS for the rads & baseboards by reading the links below that show how to do it.

    This is not to say that the contractor's plan is the only way to do the heating renovation---by all means call several other heating contractors to get additional estimates & explore additional efficient ways to modify your heating system.

    For example, I'm puzzled when you say you have partial electric heat baseboard---if at all possible try to have the contractor eliminate this high cost portion of your heating system & try to get hydronic baseboard in there instead.

    It is quite common to modify older hot water systems to partial radiant as a way of heating the floors especially of the bathroom for added comfort, and sometimes the kitchen, as well---a 3-way mixing valve zone is used at the boiler to send 120 degree hot water thru the sub-floor heating pipe loops
    to accomplish this.

    Be aware that many heating contractors are not familiar with some of the modifications that involve radiant heat components---so you may have to shop around until you find one who has done it all before.

    Also Gopogle "A little floor warming please" (with the quotes) to get an article (PM magazine site) that explains how a low-temp radiant loop is connected to a standard boiler radiator high-temp system.

    http://advice.thisoldhouse.com/showthread.php?t=3820
    http://advice.thisoldhouse.com/showthread.php?t=1639
    http://advice.thisoldhouse.com/showthread.php?t=5571
    http://advice.thisoldhouse.com/showthread.php?t=5085
    http://advice.thisoldhouse.com/showthread.php?t=11753
    Last edited by NashuaTech; 08-11-2009 at 05:53 PM.

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