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How much hot water heating can be added to steam boiler?

malex Member Posts: 106
Hi folks,

I have a small walk in closet where the previous owners had removed the radiator (thankfully the valve was holding tight). I found a small radiator, connected it and then discovered why it had been disconnected - rusty water was ouzing through the exterior stucco. I don't even want to think about what the inside of the wall looks like.

I have a HW zone off my steam boiler for an addition on top of the garage so I am thinking it may be easier to replace the broken steam pipe with a flexible HW pipe and it may be better as well as I could keep the temperature constant and low, just high enough to knock the chill out.

I am also thinking about using a HW zone to heat the basement once I finish it now that I have insulated the mains and I am also considering adding radiant heat to the kitchen floor.

How much HW heating can be added to a steam boiler? Obviously the boiler size is a factor but in general, are there any rules of thumb? Can I add HW zones as long as there is boiler capacity and how would one figure out the capacity?

My current boiler is fairly well sized for the connected load so I am assuming I can't add too much with my current boiler.

Thanks and enjoy your Turkey!


  • rusty water oozing

    was the leak from the union nut next to the valve?

    most likely, the replacement radiator has a spud from a different manufacturer to the valve, and they only work as a matched pair. all you need to do is to buy a new steam valve [with it's spud], and change the valve and radiator spud.

    even though that entails removing the spud from the radiator, it would be easier than running a new line.--nbc
  • malex
    malex Member Posts: 106
    Bone dry connection

    There is not leak anywhere above the floor boards and certainly not between the spud and the valve. And the ouzing happens midway up the wall so the pipe must have broken or maybe there is an union in the wall.

    There used to be a roof leak in that area so maybe the pipe corroded?
  • JStar
    JStar Member Posts: 2,752

    Don't go more than the pickup factor of the boiler. That can be hard to judge, unless the boiler is sized correctly. Typically, it will be between 15-30% of the boiler's output.
  • Enreynolds
    Enreynolds Member Posts: 119
    I may be all wet,

    But it seems to me that if you have a steam leak of that magnitude in your piping, you are going to have to address it in some manner, whether it be repaired, or capped off at the main.  You also do not know what kind of hidden structural damage has occurred.  To me, it would probably be more cost effective to fix the existing pipe and any associated damage, rather than running new pipe, buying a new pump, plumbing the boiler,  and then fixing damage that leak caused.

  • malex
    malex Member Posts: 106
    Good points

    Thanks Eric, I think you may be right. There may be more extensive damage that needs to be addressed. For example there is an electrical line (BX) line that runs to an outside fixture in the same wall and it is dead. I am thinking its related.

    But like I said, the boiler is plumbed for HW so it should be limited work to add a zone, no?
  • malex
    malex Member Posts: 106
    edited November 2012
    Remoed duplicate post

  • Enreynolds
    Enreynolds Member Posts: 119

    Missed the fact that you already had hot water zone for the addition.  To me it does not make much sense to run a hot water zone to this small walk in closet, which is in your steam zone.  It would need its own thermostat and zone valve.  Also, think of the poor guy that has to figure this system out in 80 years.  I would keep it simple and keep the steam zone and hot water zones geographically separate.  I think in the end it will cost less.

  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    Still Connected?

    If I am understanding the situation, the steam line to the walk in closet is still connect and only the valve is shut off.  So, that means that steam is still coming up that line, right?  If there was a leak in the riser, you sill have a leak in the riser.  Better find out what's going on and then fix it right. 
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • malex
    malex Member Posts: 106
    Still connected but no leaks

    Its a fairly long riser and the leak appears to be at the end close to the radiator. It seems the steam does not reach the leak when the rad is shut down and I assume that the air in the riser has nowhere to go and therefore compresses and essentially acts as a plug although I am not sure why it is not escaping through the leak. Maybe it is, but not at the rate as when the rad is turned on.

    I will have to open up the wall at some point to check it out and I do plan to fix it right. The reason I am asking about switching it to HW is that it is a small space with hig heat loss (closet with window and a sloping ceiling in a 1939 cape/colonial).

    I have a 1/2 bath also with high heat loss as it has 5 cold sides and when the steam comes on it stays warm for a short while but then the rad loses heat and since the thermostat does not need to call for heat it stays cold until the next cycle. My thinking was that it may be better to keep the closet at a low constant temperature as it just clothes in there and it does not need to be hot but right now, with no heat there is a lot of cold are coming from there making the bedroom uncomfortable.
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