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old steam system replacement

OldHouseBenOldHouseBen Member Posts: 1
Hi all, I'm trying to figure out the best way to replace my current heating system with a high efficiency system that provides comfort and a quick payback. Every HVAC contractor I interview has a different opinion.

Current system: 35 yr old oil-fired steam boiler, original steam radiators, indirect DHW coil w/ no storage tank. cost me about $2500 in oil since August last year.

House: 1931 2-story colonial in MA. 1750 sqft. Uncond basement & attic, both accessible. No A/C (but I would like it). No access to Nat gas, but propane is an option.

My thoughts are leaning toward some sort of combined system. Radiant floor heat on 1st floor & either hydro-air or multi-split heat pump (ducted) on 2nd floor. This gets comfortable heat in house and A/C in bedrooms for hot summer days, all without tearing house apart. I wonder about the ease and efficiency of doing a combined system like this.

Can radiant floor system act as cooling if unheated water runs through the system in the summer? Does this have any issues? Does using radiant + hydro-air cause issues if running at different temps?

Any other suggestions?

Cheers, Ben


  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    Looking for efficiency

    Even if the boiler is not leaking now, with that mileage on it it may soon be time for a replacement. Is this 1-pipe or 2-pipe?2

    Download the SlantFin heat loss app from their website, and find out what your heat loss is. Then download the radiator sizing chart and calculate the EDR of your radiators. Compare the btu of the heat loss with the total EDR of the radiators, and see how they compare. Next look at the rating of your boiler, from the plate on it and see if it is oversized for the EDR of the radiators.

    If your boiler is oversized by a sizeable percentage, then a new correctly sized boiler would save money. Is the present boiler piped properly? If not then that will be a fuel wasting situation. Is the pressure lower than 2 psi (basic function, or lower than 8 ounces for economy, and comfort)? Is the venting in the system adequate, or are you burning extra fuel to squeeeeeze the air out of some constipated little vents?

    Conversion to hydro air may not be cost effective, as radiators need no electricity. Mini split units would provide the cooling you would like.

    Post some pictures of your boiler and it's piping for us to see.--NBC
  • Jamie HallJamie Hall Member Posts: 6,653
    It sounds

    as though for some reason you are not contemplating updating the steam system as one of your strategies.  May I ask why?

    It is true that a really well installed system such as your have described (either option) can have a greater efficiency than a steam system -- by a rather small margin (a modern steam system will run around 86%; an equally modern hydronic can run around 94%.  But -- what is the payback?  You should run the numbers yourself -- but I expect you may find that over the lifetime of the equipment upgrading the steam system will be no more expensive than a whole new system.  In fact, it may well be less.

    Unless you are sold on ripping out the steam for some philosophical reason, I recommend that you get some quotes from reliable and experienced contractors on each possible option, including expected energy usage and including all expenses (all energy plus equipment depreciation and maintenance, etc.) and then doing a very very careful cost benefit examination.  You may be surprised...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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