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Adding a steam/water radiator to existing baseboard

Dynamwebz Member Posts: 13
I own a 1923 Bungalow. Lots of great looking interior wood. I'm currently performing a whole house remodel one room at a time. The house has old slantfin hydronic baseboard heat throughout the house. The steam radiators were removed decades ago. The slantfin is ugly. I want to convert to hot water radiators.

The house has a gas fired water boiler. Sized appropriately for the house 5 years ago. The slantfin is one continuous loop around the house.

I have purchased (with the promise of an easy return if I need to) a radiator about the same size as the previous radiator. I basically measured the scars on the floor and purchased a hot water radiator with the same footprint and high enough to almost reach the window sill. It was already disassembled, cleaned and painted. It has all the holes plugged.

So, how do I do it? I really don't want to simply cut the copper loop and stick the radiator into the loop. That is, I dont want the radiator as part of the loop. I want to be able to control how much water each radiator gets to be able to regulate the temperature of each room.

I know I need to install the little silver air release valve in the hole near the top of the radiator. Do I need any other type of special gizmo? Other than the main water control valve?

Do I "T" off the copper loop and fit the copper to some type of connector I can get at a plumbing supply store and connect to the bottom hole of the radiator? Then basically do the same thing on the other side top hole fot the return? If so, how do I return the cooler water to my copper loop? I would think I need some type of one way valve on the return side. Otherwise the pressure would be the same on the inlet and return which would basically not allow any water into the radiator after the initial charge and air bleed.

Or, do I need to create a manifold board near the boiler and feed each radiator from a separate valve and return to a common manifold? Probably the preferred method of Rich Trethewy but obviously the most time consuming and expensive.


  • Dynamwebz
    Dynamwebz Member Posts: 13

    I just found out about monoflow t's. Sounds like what I need?

  • Steamhead
    Steamhead Member Posts: 15,635
    Basic Problem:

    the thermal behavior of a cast-iron radiator is vastly different from fin-tube baseboard. This will cause comfort issues.

    Cast-iron has a high thermal mass. It will heat up more slowly and cool down more slowly than low-mass radiation such as your baseboard. So some rooms will randomly seem warmer or cooler than others.

    If you're serious about this, do a heat-loss calculation on every room in your house, and get a cast-iron rad for each. Then we can talk about piping.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Dynamwebz
    Dynamwebz Member Posts: 13
    Serious? You betcha!

    I understand the thermal behavior is different between 2 vastly different types of heating conduits. I have lived in a house with steam radiators and a house with hot water radiators. Liked the stream best.

    This is a work in progress. One room at a time. This is not a simple paint the walls thing. It's new ceilings, skip coat old horse hair plaster, strip and refinish vast amounts of old pine window, door and baseboard trim, wood doors, sand and refinish the floors. So getting a bunch of radiators installed first is out of the question. And the first room is complete but for paint and heat.

    The old steam radiators were removed before I purchased the house. From what I read, they heat to a higher temp than hot water radiators. Obviously. I am using the footprint of the old radiators to size the new ones. Close enough since I have added wall, ceiling and attic insulation.

    My GF had a couple of rooms added to her house a few years ago. They installed baseboard heat. She has hot water radiators in the other rooms. She said she had to fuss with the radiator valves a bit to make all rooms the temp she wanted.

    I also supplement my heat with a basement wood stove. So I am used to uneven heat throughout the house. This is more for aesthetics than anything else. Too cold? Wear a sweater. Too hot? Take it off.

    Tell me how this sounds and if I have missed anything. And I can sweat a copper tube and turn a pipe wrench.

    I remove the slantfin. In the basement I extend the 3/4 copper to replace the void left from the slantfin removal. I add 2 monoflow T's making sure I have them correctly orientated. I connect 1/2" copper off the first T and using an approved reducing pipe, connect it to the bottom of the new radiator while adding a wheel valve. I have seen the new type thermostat valves but they are not period to my house. I connect another pipe to the top of the opposite side of the radiator, drop it through a new hole in the floor and then reduce it to 1/2" copper and connect it to the 2nd monoflow T. And I add a bleeder valve in the appropriate hole near the top of the radiator.
  • Paul48
    Paul48 Member Posts: 4,469

    do reallize that some cast iron radiators are for steam only, and some are for either? You seem to be mixing terminology, that's why I'm asking.Do you have the right type of radiator?
  • Dynamwebz
    Dynamwebz Member Posts: 13

    Yes, I was careful to get a hot water/steam radiator. Not a steam only radiator.

    There's a warehouse in New Bedford Ma, New England Demolition and Salvage. They sell used radiators by the truckload. The owner is very knowledgeable and upfront about all his in stock radiators. I purchased a re-fitted hot water radiator.

    I will be going there frequently to pick out matching and sized radiators to have him send out for re-fitting. Re-fitting is a task I don't care to undertake.


    Which terms were mixed? I have mentioned that my house once ran on steam heat. But it was converted to hot water over 25 years ago. And by doing so, destroyed a lot of character which I am attempting to restore.

    I understand why people seem hesitant to offer advice here. But as I stated, this is a work in progress that will not be sidelined for a lack of knowledge about a particular segment of my remodel. I will learn one way or the other.

    Yeah, I'm a desk jockey but I have a lot of mechanical aptitude and skills. I have a woodworking shop in my basement and build furniture in my spare time. I was a heavy motor vehicle mechanic in the Marine Corps. I can turn a wrench.

    I always map out the technical issues before I pick up a tool. That's all I'm attempting to do here. I don't want to miss anything. But performing a heat-loss exercise and installing all the radiators at once is simply not feasable right now.

    So, how did they do it in 1923 when my house was built? They had a few beers and guessed, from experience, how many and what size radiators to install.

    I don't expect this to be perfect, just functional and as period correct as I can get it. Minus the horse hair plaster.
  • Paul48
    Paul48 Member Posts: 4,469
    edited July 2012

    that we don't know the skills,or understanding of the folks that come here. There are people that think they could put a steam radiator on a hot water system , and get more heat.I'd do a room by room heat loss for future radiator purchases. It's simple to do, and you'll properly heat the rooms. Monoflow should work fine. You only need one monoflow tee, unless you are feeding down. If no one else does, I'll post a link to slant/fins heat loss program, this evening. I'm at work.
  • Dynamwebz
    Dynamwebz Member Posts: 13
    edited July 2012
    feeding down?

    Not positive what that term is in reference to, but I'll give it a guess.

    I currently have a single loop. I will crack into this loop for room rumber 4 of 7 rooms. So yes, there are 3 more rooms in the loop after the current room.

    So, I take it that the last room only needs 1 monoflow T?

    And yeah, I get the "can I burn jet fuel in my sub compact and triple the horsepower?" questions.

    As of this past weekend i didn't know there was a difference between the 2 radiators. But the man from the home reclamation company gave me an education.
  • SWEI
    SWEI Member Posts: 7,356
    how did they do it in 1923?

    Dan has a number of books that go into detail on the ways our forbears designed and sized their systems.  Suffice it to say that they used a number for formulas and charts which got the job done for the buildings and technology of the time.  Really.

    While we now have far more tools available to us both in terms of system design/sizing and system installation/control, America is in the unfortunate situation where only a minority of our practicing professionals truly understand how to use them.

    A proper heat loss calculation is essential before you move forward.  It's not that hard to do.
  • Paul48
    Paul48 Member Posts: 4,469
    Re: Feeding Down

    Say the boiler was on the first floor and you wanted to feed a radiator in the basement.It takes more to get hot water to go down, and therefore requires 2 monoflow tees. The first in line acts as a scoop of sorts to divert water into the radiator, the second  creates a venturi to suck the water from the radiator.
  • Dynamwebz
    Dynamwebz Member Posts: 13
    edited July 2012

    So the force of the water entering the radiator from the monoflow into the radiator has sufficient force or pressure (with the siphon effect of the water still moving thru the copper loop) to to push the water past the discharge side of the radiator and back into the 3/4" copper loop without adding the 2nd monoflow which in turn would add the venturi effect. Unless I was pushing water down to another floor.

    So if I had a loop on the second floor, the last radiator in the loop would need that 2nd monoflow to push the water back down (past the first floor) and into the basement boiler? Good to know since the plan would be to install radiators into the newly renovated attic rooms, should all go well with the first floor. Just 2 small radiators needed since I over insulated the attic. Hmmm... maybe a couple short lengths of cast basebord would do the trick.
  • Paul48
    Paul48 Member Posts: 4,469

    Because after the last radiator on the loop the water has no choice but to return to the boiler.So the second isn't needed there either.Read some more about them. There's all the info you could possibly want,  right in front of you.
  • Dynamwebz
    Dynamwebz Member Posts: 13

    Been reading about the monoflow T's.

    Everyone has an opinion and they don't all match.

    I found this page: http://www.comfort-calc.net/monoflo_system.html

    The author states that on my type of system, assuming I had all the radiators installed, only 1 monoflow T would be required for each radiator, (none for the last radiator in the loop) on the return side of the radiator. The author feels that the pressure back up from the return side monoflow is enough to force the water into the radiator. And the venturi effect will create a suction at the top of the venturi aiding the water flow through the radiator. Assuming the radiators are on the first floor and the boiler is in the basement.

    Would you agree?

    Is there a minimum amout of distance the monoflow should be placed before a 90 degree turn in the main loop?

    "Pitch the main and the radiators up in the direction of flow"

    I assume this means to always have the main pipe going uphill to keep air moving through it. But does this mean to have one side of the radiator higher than the other? If so, which side? Return side I assume since that's where the air purge valve goes? Is it necessary with the air eliminator I already have installed?

    I feel the plumbing of these radiators is rather straight forward. Unlike the series of valves and piping and expansion tank and other do dads the plumber installed on my new boiler a few years ago. Seems that last boiler that was installed had a minimal amount of required assessories installed. The difference between a hack and a pro.
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