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Help sizing baseboards, new install old house.

Yuda Member Posts: 1
edited November 2021 in THE MAIN WALL
Hi, I hope I am posting this question in the right place. I own a house that currently has steam heat. I have a basement, 1st, 2nd, and soon to be 3rd floor. My third floor currently is an attic that will be turned in to a master suite. My steam system is working pretty well but I really want to change everything over to forced hot water/baseboard for the following reasons. First, I have a finished basement and the steam pipes in the basement make it unbearably hot in the winter. My wife is a personal trainer and we have a gym downstairs for her and her clients. Opening the windows down there does not help. Second, since I am doing an addition I really want my own zone for heating and cooling on the third floor which I just can't do with steam. So I figured I can kill two birds with one stone. If I ditch the steam system I can run oxygen barrier pex and have each floor be on its own zone with its own circulator pump. I have been planning out the best way to run the pipes while opening as few walls as possible. Here in lies the question, 1, I have a few steam pipes which are going from the boiler room straight up to the 2nd floor, is it ok if I cut the pipe with a Sawzall on the bottom and top of it and use it as a conduit for my pex so I don't have to open the drywall on each level to drill holes in the bottom and top plates? I plan on sending two pipes through it (supply and return). And the next question I have is how do I size my baseboards per room of the house? I understand that with a series configuration, the last baseboard on each zone tends to get much colder water than the first in the zone, are there any piping configurations that would eliminate this, short of hooking everything up in parallel? I saw a pass through valve with a dial that can be sweat soldered to each baseboard which can change how much water each baseboard gets but I can't seem to find the correct part that I need. As an example, my living room on the first floor is 32.5 feet long x 13.5 feet wide x 8 feet high. 

I'm very worried about installing all the baseboards only to find out that I either under, or oversized the baseboards while having the last baseboard in the loop not give off enough heat.

Any help would be greatly appreciated, thank you!


  • retiredguy
    retiredguy Member Posts: 878
    Why don't you have a good steam guy check out your steam system to see if you can zone what you already have. For example, you can't zone a series loop hot water system. If you need to ask just how do you do this and that, I would strongly recommend that you get the help you need. Check out the contractor section on this site for people who are well versed in what you are trying to accomplish. They will save you money and time and do the job correctly.
  • KC_Jones
    KC_Jones Member Posts: 5,692
    If you are set on ripping out the steam, then I guess that's it, but I will still give my $0.02 worth. The basement issue is easily resolved with pipe insulation, which should be done regardless of the temperature of the basement.

    You do know for additions you can add a forced hot water loop off of the existing steam boiler? If not, you do now.

    So, if you want to completely replace the whole system, you have skipped a couple steps with the questions you asked. First step, before anything else is you need to do a room by room Manual J heatloss calculation. That will initiate all the design process that follows, including how much baseboard per room, pipe size to feed the radiation, boiler sizing etc. This is a design process and can't be rushed into. And don't use any "rules of thumb", they are the purview of hacks IMHO.

    As far as using old pipes as a chase, as long as they aren't too tight in there I can't think of a real problem with that, but I would suggest several cautions and things you need to answer.

    First, are those pipes inside an exterior wall? If yes, don't do it, freezing risk is a big problem.
    How will you support the pipe after you cut the top and bottom connection, that is most likely keeping them from falling into the basement?
    What is your plan for sealing them off so the pipe doesn't become a chimney for air to flow through the house.
    Will the pipes, based on the heatloss calculation, actually fit. You think they will, but since you haven't done a heatloss calculation how do you even know you have the right size?

    Personally, and I'm not alone here, almost no one on this board will advocate for removing the steam heat, it, in all honesty, doesn't make any sense. You are talking about a mountain of work. Also, patching all the holes left from the steam radiators.

    For me, insulating the pipes like they should be, and adding a hot water zone to the existing boiler is the most sensible for what you are doing.

    I'm sure others will be along with more comments.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Jamie Hall
    Jamie Hall Member Posts: 22,891
    Step one would be to make sure the steam pipes in the basement are properly insulated and see if that keeps things down there better. Probably will.

    Second, you do not want series piping for your brand new hot water system. If you are going to spend very large dollars for tearing out the steam and putting in hot water -- which I don't recommend as it will be less comfortable and you'll never recover the investment -- at least do the hot water right either with home runs or with reverse return parallel zones. Yes, you are going to have to chop into some walls and all, but that is part of the fun and joy of destroying a perfectly good steam system and installing hot water.

    On sizing. You should do a complete Manual J on the house. Slant/Fin has an excellent program for that here: https://www.slantfin.com/slantfin-heat-loss-calculator/ which can either run on a smartphone or be downloaded to a computer. It will give the heat loss for each room and, of course, the total loss for the building. It will even recommend proper baseboard lengths if you like. Not at all hard to use. Start there.

    Use their recommendations for baseboard lengths, and the total load figure for the size of the new boiler. Do NOT oversize the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,021
    Also, those riser pipes from the basement to 2nd floor often have an offset of 90 ells under the 2nd floor. Not all are a straight shot up.
  • Robert_25
    Robert_25 Member Posts: 527
    Yuda said:

    My steam system is working pretty well but I I'm very worried about installing all the baseboards only to find out that I either under, or oversized the baseboards while having the last baseboard in the loop not give off enough heat.

    You are wise to be concerned about sizing the radiation. For one thing, a steam radiator puts out about 40% more heat than a hot water radiator of the same size. It may be tough to fit enough linear feet of hot water baseboard in some of your rooms to adequately heat the space. Also, when you have hot water baseboards connected in series it is very important that they are properly sized. As you noted, the water cools as it goes down the line, and that has to be accounted for in the design.

    About the basement being hot - your steam pipes need to be insulated.

    The good news is that you can insulate the steam piping and add a hot water zone in your new master for a small cost compared to tearing open the walls and installing a new hot water system.
  • Jamie Hall
    Jamie Hall Member Posts: 22,891
    If you do choose to run a hot water baseboard loop in the new zone -- not a bad idea -- many baseboard designs have enough space in them to run a return pipe in the same baseboard. If that's what you choose for your design, then you can easily run a reverse return parallel system and get rid of the problem of the heat loss in a series arrangement.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,021
    Or if you want AC on your new addition, you can put a hot water coil in the air handler along with the AC cooling coil. The hot water would come from the steam boiler thru a heat exchanger.
    You do NOT want to put the air handler in the cold attic, rather in a closet in a conditioned space. Ductwork in cold attic is no problem.
    EBEBRATT-Ed Member Posts: 15,300

    You just can't do this willy nilly and expect a good result.

    You have to do these things in order

    1. Heat loss calculation of the total house and each room

    2. size baseboards and locate baseboards based on the above heat loss along with the average water temperature your going to run. (usually 180 deg average, 190 out and 170 back) with a 20 degree water temp drop you will get 10.000 btus for each gpm circulate

    3. Make piping layout and size pipe
    4. Pick the boiler