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Oil to Gas conversion: hybrid with hydro air handler in attic for heat and cooling upstairs?

smithers Member Posts: 1
We have an 1800sq-ft two-story home in Boston area built in 1929, with

single pipe steam heat, run off oil-fired boiler that is 40 years old

and inefficient. We plan to switch to natural gas, install new high

efficiency Alpine boiler and indirect hot water heater. our hvac man says he

can rework first-floor radiators for forced hot water and add return

lines, but very hard to get return lines from upstairs radiators without

tearing house apart. Since we also want AC upstairs, he proposes

installing an air handler in the unfinished attic with a heat coil

(hydro air unit), and running hot water pipe from new boiler up to

attic unit to provide forced hot air heat via new ductwork in attic to and

from the four upstairs rooms through ceiling vents. He will also tie

this air handler into a new AC unit to be installed outside house, to

provide upstairs cooling in summer through the same new ductwork.

So we would have a hybrid system, with forced hot water radiators on

first floor and in finished basement, and forced hot air on second

floor, both running off the same new HE boiler. And we would get AC in

the process. (We have just done blown-in cellulose insulation in walls,

and air-sealing, so house is pretty tight). This HVAC plan makes sense

to me as a layman.

My major concern is the proposed ductwork in an unconditioned attic that

gets mighty hot and mighty cold. We have a good vented roof. Is this

system okay if insulated and sealed well? How much energy loss? Any


Thanks for guidance!


  • Steamhead
    Steamhead Member Posts: 16,830
    edited July 2012
    First of all

    trying to change a steam system to hot-water is risky. You will be running some ten times higher pressure for hot-water than for steam, which WILL find any weak points that exist. I've seen some serious building damage from ill-advised steam-to-water conversions.

    Another problem is that steam radiators give off a lot more heat than hot-water ones. If you try to use your existing radiators on hot-water, they may not give off enough heat when it gets cold outside.

    Factor in the type of boiler he is proposing, which may require some sort of water and system cleaning and treatment to avoid damage to the boiler from system dirt. Then there's the fact that boilers of this type use a lot of proprietary parts that may be hard to get quickly if the unit breaks down.

    We don't do these conversions, and these are a few reasons why.

    The contractor you've been talking to obviously doesn't know steam and probably doesn't care. Otherwise he would know that a steam system which is using more fuel than it should can be easily fixed, for far less money than I'm sure he wants for his proposal.

    As for replacement steam boilers, the best ones are wet-base, power-burner units. Look at these threads for examples:



    If the oil company has been "maintaining" your existing boiler, that could be part of the problem:


    And here's one where we converted the existing oil-fired boiler to gas, as well as de-knuckleheading it:


    There are plenty of Steam Men in the Boston area. Go here:


    Even if well vented, an attic like yours is still an unconditioned space, and since the typical duct system loses some 20% of what goes into it, you'd pay an arm and a leg to run that A/C setup unless they were real careful insulating and sealing the ductwork.  And even then you'd lose efficiency. A ductless mini-split system would sidestep this problem.

    Keep the steam, replace (or convert) the boiler and use a mini-split for your A/C. This will give you the best combination of efficiency, comfort and reliability.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Some other info...

    I agree with Steamhead and would like to add a little more info.  While I fully support the use of hot water heat, converting from steam to hot water rarely makes sense economically and in terms of comfort.  It also has a number of disadvantages. 

    Boilers like the Alpine and all other modulating condensing boilers (mod con)achieve thier very high AFUE numbers with several sacrifices.  The first is a many fold increase in electrical usage due to at least one if not two pumps are running all winter, a draft fan, and the power to run all the electronics.  A safe number is a tenfold or more increase in electrical usage over a typical gas steam boiler (no power burner)

    The second is the inherent complexity of the unit is going to cause higher repair costs over the life of the unit.  They are much more susceptible to power surges from the electric company or lightning.  I recommend the same surge protection equiment as you would use on a good computer.  Even then, you can blow the main board and end up with a very expensive repair with parts that may need to be ordered.   With a steam boiler you usually just blow a little inexpensive transformer, which you can pick up at most hardware stores and every contractor stocks.  Blown transformers are very rare since they are not especially susceptibel to power problems.

    The third is a much shorter life.  The expected life of most units in the 20 year range with proper and very thorough maintenance.  For a steam boiler it is 30 years or more.

    With your current system, you also can easily add room by room temperature control, which would likely completely balance any gas savings you might achieve through the use of a mod con boiler and give yo better comfort.

    Forced air systems are widely documented to create far higher levels of building air leakage and, as you already raised, ductwork heat losses/gains. Ducted systems for heating are non existant outside the US, and are being used less and less for cooling.  Here are some links to documentation.

    Report of ductwork leakage and increase in heat loss of homes  [u][size=12][color=#0000ff]http://www.ornl.gov/info/reports/1991/3445606042546.pdf[/size][/color][/u]



    From: http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12530

    Specifically, AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere. AFUE doesn't include the heat losses of the duct system or piping, which can be as much as 35% of the energy for output of the furnace when ducts are located in the attic.






    Lastly, an item  rarely discussed in residential setting, but taken seriously in commercial settings, are the issues of smoke and flame spread inherent in ducted systems.

    Find a real steam specialist, keep the steam, upgrade the boiler, use thermostatic radiator valves for room by room control. and get some nice quiet and efficient ductless split units.  In doing this,  you'll have about the most efficient and comfortable  heating and cooling avialable.  The heating system will be designed specifically to do its job well, and will the cooling.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
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