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Changing convector heating units to baseboard on a one pipe system

ron86ron86 Member Posts: 2
I have a customer that wants to remove two recessed and one wall mount convector unit and replace with baseboard. The three rooms involved are on the upper floors of a split level home. The hot water system is one pipe with a one inch main with half inch risers and diverter tees spaced roughly the same width as the convector cabinets. I was considering piping the existing supply and return lines through the baseboard cabinet, running them side to side above the element then connecting to the elements themselves. The existing convector cabinets are 56" wide (2) and 36" wide (1). I used the "Every Darn Radiator" book to convert the units to baseboard (I could not specifically identify the manufacturer, but found charts with all the correct measurements and figured it would be pretty close) and came up with equivalent baseboard runs of 18', 11', and 18'. I also did a heatloss calculation using Slant Fin's software package, on that I got baseboard runs of 8', 6', and 14'. Two questions; 1- Is attempting to make this change feasible? 2- If it is, which method of determining the amount of baseboard is the better way to go. Any insights will be greatly appreciated.


  • IronmanIronman Member Posts: 6,164
    You need to determine the actual btu rating of each convector and size the BBS to that. Figure 500 btus per lineal foot of standard B.B. at 170* average water temp. Don’t use the 580 btus that’s published. That’s at 180* which you won’t have.

    The best thing you can do as far as piping goes is to put the new stuff on a separate loop and circulator back at the boiler. What you’re describing will add additional head to the new part which will give you little or no flow if you connect it back to the monoflo loop. Monoflos are very touchy and adding more piping in the runouts is asking for trouble.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 8,040
    If you found the convector BTUs as close as you can find and converted that to the number of baseboard feet you will be fine. Just make sure the water temp used for the convector rating is the same water temp used to size the baseboard.

    If you feel your convector ratings are reasonably accurate then use the longer baseboard lengths you sized (18', 11' and 18'). using the shorter lengths you sized with slant fin will throw the rooms out of wack with the rest of the house.

    You only need about 1 gpm of flow through the 1/2" copper branches to supply the heat you need for 18' of baseboard 1/2" is good for 1.5 gpm so you should be fine.

    I am sure that the resistance of the new baseboard even with the extended pipe will be less flow resistance than the old convectors. I think your fine
  • SteamheadSteamhead Member Posts: 14,192
    I think you will need to move the diverter tees so they are the same distance apart as the baseboard is long. Can't put my hands on it at the moment, but the reason should be in @DanHolohan 's book "How Come"?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • DanHolohanDanHolohan Member, Moderator, Administrator Posts: 15,148
    That's to give more pressure drop along the run so the water flows to the branch. You need two diverter tees when the convector is on the second floor and you're feeding from the basement.
    Retired and loving it.
  • IronmanIronman Member Posts: 6,164
    edited September 2018
    Two diverter Tees and wider spacing may still not be enough for what the OP is describing. He's planning on running the s/r piping the length of the BB which would effectively double the length. That's why I suggested a separate loop.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 8,040
    Yes the diverter tee and the supply tee should be piped the length of the baseboard apart.

    My point is the convector heated the room before. I would think the convector coil would have more resistance than the 1/2" copper to and from the baseboard
  • ron86ron86 Member Posts: 2
    Thanks to all of the responders for the input. The idea here was to give the heating units in these rooms a facelift switching from convector cabinets to baseboard and keeping the renovation contained within the room. I understand the points you are making but would have to get very invasive throughout the house in order to change the tee and diverter tee locations as well as riser locations. Would I be better off suggesting panel radiators as an alternative?
  • Big Ed_4Big Ed_4 Member Posts: 1,572
    edited September 2018
    The top floors of the split have higher heat loss then the lower level . Garage below , over hangs , more ceiling square footage . Best off zoning each floor or wing for comfort ...

    Connecting to the MonoFlow system. The risers and tees are spaced for the length of the radiator , You will lose some pressure drop extending out the radiation ( pressure drop creates flow). You will also need to keep an uphill pitch to the air bleeder. Also the curse of baseboard is that it takes up wall space . Furniture blocking the flow of convection will eat away on your calculations . Sure add extra , then the pressure drops further and you need more pitch . What will also would fool you when adding baseboard to an existent MonoFlow system and risers ,it will heat up if install somewhat correctly . Until that phone call on the coldest day of the year.

    I would recommend two options ,zone for baseboard or replace with panel radiators . Panel radiators I feel would be the best choice . I would over size (normaly you will for the properly size of the given space ), add diverters and the TRV's. Rough in using the existing risers , finish the room and hang the radiators. Each room can be set desired comfort level . Which solves the problems with single zone split levels . The radiation will be installed on the best unused space of the room with plenty of output 40% +- of which would be the nice radiant heat . Once they fall in love with comfort they would want them in the rest of the house . Then add that condensing boiler with an outdoor reset....

    I have enough experience to know , that I dont know it all

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