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Thread: edr boiler size

  1. #1

    Question edr boiler size

    If a vendor says his edr for measuring steam radiators is, say 300, is it better to step down to a boiler with 270 sq ft or step up to a boiler with 350 sq ft? I know you do not want a boiler that is too small or is too big. If the installed boiler is too small or too big, what "fix" can be done? Is there really that much difference between the 270 and 350 ? These are both at the low end for Burnham with sizes that range from 158 to 725 (models IN3 to IN9)

    Again, I have an old one-pipe steam radiator system converting from oil to natural gas, hopefully. Boy, I'm nervous.

  2. #2
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    You must size a steam boiler to the radiation. Under sizing will cause problems. We look for proper insulation and generally use listed IBR outputs for steam .

    It is all about the designer/ installer. I advise clients to call around for local service companies and ask to talk to their knowledgeable steam man.

  3. #3
    In the Trades Tom Sawyer's Avatar
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    Small is always an issue. Slightly larger can be dealt with.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Retired Defense Industry Engineer jadnashua's Avatar
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    This may be simplistic, but (this is my take on this, and may not be correct!) your steam boiler must be big enough to actually be able to fill the entire system with steam before it can cool off enough and condense. Since if it can't, there's no way to get steam to all of the radiators. Course, having a huge excess capacity is a waste, but too little is worse. It's still important to try to 'right-size' it.

    Now, if you were to do a bunch of improvements in insulation and tightening up the house, you may not need all that radiation, and if you changed them to smaller units, you could get by both in comfort and performance with a smaller unit, but it would not work well at all if you tried to use a smaller one before that happened.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5

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    I had a chat with someone who just did his house (a house flipper) doing the work himself. He converted steam rads to hot water baseboard. My pipes are not in the wall, so that problem is not there. I'm told "parts" are cheap for baseboard - a couple hundred a room and pax piping (though holes I already have in floors of this 2-story house?). He said the cost is really the labor. And that means using a high efficiency gas boiler. Now with my steam rads I can only get a new 82.3 AFUE gas boiler.

    Your thoughts?

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you can do the labor, modulated hot water radiators are more comfortable than steam heated ones since they will tend to be constantly on at a lower temperature than steam which will be on and off. Depending on their condition, it might be possible to take the plugs out of the radiators and convert them to a two-pipe configuration, but the steam may have a lot of rust and crud inside them making that difficult to impossible. The high thermal mass of the existing radiators will provide nicer heat than new baseboard.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the trades Dana's Avatar
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    Installing a high-efficiency boiler and converting the system to pumped-water is not a cheap thing to do either. Ripping out a steam system and installing a more appropriately sized (for the heat load) cast iron boiler + baseboards is likely to be north of 10 grand, and any conversion going with a modulating condensing boiler is likely to come in twice that.

    Going from radiators to cheap fin-tube baseboard is a big step down in comfort- I can see why a house-flipper might go that route in a project house, but not so much on a house you were fixing up to LIVE in for the next decade or two!

    Re-using CAST IRON baseboard or re-using big pumped-water cast iron radiators can be almost as cheap as fin-tube, even after you've sandblasted & painted them, but you have to size them correctly for the loads of the rooms to get the balance right.

    Converting 1-pipe steam can be labor & plumbing intensive, and may or may not have sufficient radiation to deliver the heat at condensing-boiler temperatures (but usually would at 83% efficiency hydronic cast iron boiler temps.)

    Before doing any conversion, do a room by room heat load calculation. Almost all cast-iron boilers are going to be 2x oversized for the true heat loads of average sized houses in NJ, but whether a modulating condensing boiler would ever pay off in within it's anticipated lifetime depends on your anticipated fuel costs.

    If the oil boiler isn't some ancient asbestos-clad piece o' junk it may make better financial sense to install a conversion burner, or to install a couple of mini-split heat pumps and only use the steam for backup (and enjoy high-efficiency air conditioning too.) With the new or cleaned up radiator vents (thermostatic vents, if you want to micro-zone) even a 1980s vintage steam boiler on a system with insulated pipes can deliver ~75% efficiency or slightly better with a conversion burner. If older than 1980 it probably has high standby loss, especially if it doesn't have a flue damper (either barometric or ignition-cycle automated.) If the boiler room is the warmest place in the house on design day, it's probably worth getting rid of it.

  8. #8

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    Thank you everyone in this and a few other posts here for all your help. I bit the bullet and signed a contract yesterday to convert my steam boiler from oil to gas. And today's paper has a great article saying the natural gas price in NJ is going down again this winter.

    Dana, I also took your advice on the low hot water use, and that stand-by heat loss is what matters, not the cost of the source. I ordered a really well insulated electric hot water heater that has a great full coverage warranty for 9 years for $110 (and free annual check-up) and also understand 1) with low fresh water input, corrosion risk is lessened, and 2) my annual cost should be a fair amount less than the Energy Guide which is based on a normal household, not a single household like me.

    You all really, really helped me. Thanks again.

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