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Imminent & Urgent Decision - ModCon or not with HydroAir

Steltz Member Posts: 7
Hi All,
This decision is essentially made for me, and I want to make the best one at this point. I let my oil tank run dry. Got a delivery Sat. morning, and it wouldn't fire. Pulled about 12 gallons of milky/watery looking diesel out. Sunday changed all filters, pulled 1-2 more gallons out, and was able to fire it up. Went out early this morning (nighttime-AM), I fired it back on, and now it's out again. My instinct tells my there is water getting into my tank. EIther way, I'm moving on and switching to gas (I have a 250 meter) and deal with oil tank nightmare after.

Sorry for the boring details. I have hydro air with two 70k btu coils in my house with IDH. I would like to go wall-hung mod-con boiler. My question is will I actually benefit from a mod-con? I don't know enough about my coils/fan to know how low I can set the water temp. If I have to send 170+ degree water does it make sense to have a mod-con?

Separately looking at a Navien or Viessman B1HE. Would love views but more importantly the question of should I even have a modcon? I am hoping to have this project started by Wednesay the latest so any help is very appreciated!

Thank you,


  • GGross
    GGross Member Posts: 186
    Even if you do not utilize the savings that condensing appliances can offer you would still be taking advantage of the other part of "mod-con" which is modulation. Go with a mod-con boiler, properly installed. As far as which one to purchase? I am an unashamed Viessmann fan, however no matter what you buy, you should only purchase equipment that has local parts and support.
  • mattmia2
    mattmia2 Member Posts: 5,737
    Between Navien and Viessman I would pick Viessman. There are others compared to Viessman that would be tougher choices and might depend on how I want to control things.
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    You need to determine your heat loss first. Using the oil receipts is a good way.

    There are hydro air handlers that can use condensing temperstures, yours might work just fine at lower temperatures with lower air flow. One question is: why a boiler at all? A furnace and/or heat pump would work just as well. 
  • hot_rod
    hot_rod Member Posts: 16,552
    Get the data on the coil and see how it performs at lower temperatures. It’s possible to supply as low as 129F to hydro coils if they and the duct work are sized for those low SWT conditions 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 12,145
    Viessmann is top of the line. I would stay away from Navian, they don't rank near the top
  • pecmsg
    pecmsg Member Posts: 2,954
    You will only see savings when the supply water is below 140*. 
    I’d guess 1/2 the time!
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,725
    You only changed the filter. You need to blow back the line, then change filter, strainer, nozzle.
  • heathead
    heathead Member Posts: 191
    Hydro Coils. Each 70 btu. Have you done a heat loss? Then where are the hydro coils located? Could you just install a 90 plus gas furnace in one or both ? What do the venting options look like? I think effiency wise a 90 percent furnace if possible is much more cost effective install and operation wise.
  • Steamhead
    Steamhead Member Posts: 15,429
    The main advantages of hydro-air over furnasties are- 1: If the heat exchanger leaks, exhaust gases won't get into the ductwork, and 2: you can put the air handlers in places where venting a furnasty would be impossible.

    But no ducted heat system will ever approach the comfort level of a true hydronic or steam radiator or radiant system.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,334
    pecmsg said:

    You will only see savings when the supply water is below 140*. 

    I’d guess 1/2 the time!
    You WILL see savings when the modulating gas input is lower that the maximum input. (which is like always). @pecmsg means You will not see the higher efficiency of the condensing boiler when the return water temperature is higher. But you may be able to operate at lower temperature water in the spring and fall (See @hot_rod above) by operating the fan at a lower speed to get more heat from the low temperature water. Switch to the higher speed when the outdoor temperature drops.

    So it's not radiant floor heat pecmsg... It is more efficient than the oil boiler he is replacing.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Steltz
    Steltz Member Posts: 7
    @mattmia2 Thank you! Getting that sense.

    @Hot_water_fan My house is a sieve at the moment. Still have insulation work to do. So at this point it has to be do what makes senseand hopefully there's system flexibility. The modualtion part, I suppose? Can't really do a furnace because I have hydro air-handlers. One in the basement that feeds first floor. One in attic that feeds two zones - second floor and attic (two bedrooms up there). Heat pump, maybe. I just don't know enough. My contractor mentioned inverters that utilize freon....no idea though.

    @hot_rod I guess I'll have to go digging into what I have - wasn't clear from the paperwork in my email. I'll look when I get home. Logically, I assume the ductwork would have to be smaller for a lower SWT?
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    @steltz if you ever want AC, now is your chance! Otherwise you’re doubling up on equipment