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Replace tankless coil with tankless coil or go indirect?

Hey Guys,

I would like to appologize in advance. I'm sure this issue has been covered on here before but most posts i've found have been with regard to full system replacements or new installs.

Here's my situation-

The tankless coil in my 15 year old peerless oil burner has been having a hard time keeping up with the hot water demand of the bathtub/shower. When i had the furnace guy come by today to clean out the boiler and ready it for winter, i mentioned this to him. He recomended that i change my mixing valve but also stated that the poor preformance of the coil could be due to calcium buildup from the hard water that i have. I find this fairly beleiveable as my parrents weil mclain oil burner's tankless coil can keep up with a hot shower just fine.

So i asked him if i should replace the coil. He said the coils are very inefficient and recommended that i consider the indirect water heater instead. The coil change was $700 and the indirect heater option was $2000. He seemed confident that within 5 years the indirect solution would pay for itself.

From my research thus far, i've learned that one of the reasons that the indirect soultion is most efficient is that during the summer months the furnace can be shut down and will only have to start to heat the water in the storage tank. Now, my furnace guy stated that with the tankless solution i should set the low end of my controller to around 100 degrees in summer months as the cast iron boiler isn't designed to be shut down cold and brought up to temperature on a day to day basis - this seems to make sense.

My question is if it would really be worth it to pay the $1200 extra for the indirect solution if i have to keep my furnace at 100 degrees just to heat the water in the tank. I'm almost thinking i'm better off just replacing the coil. What are your thoughts?

Thanks in advance


  • Zman
    Zman Member Posts: 7,573

    I would install the indirect. You will save the money over the long haul.

    I would never set a cast iron boiler to 100 degrees, the condensate will destroy the boiler and flue. Non-condensing boiler should run with a return temp above 140 degrees.

    I have heard the cast iron boiler myth before. It is not true. there are countless cast boilers running with simple on/off controls.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • billtwocase
    billtwocase Member Posts: 2,385

    with Zman. An indirect will save you $$$. Just don't discuss or mention  price here. The controls and zoning should run your burner the most economical way without you needing to manually adjust it seasonally.
  • bob eck
    bob eck Member Posts: 930
    How to heat hot water

    I would go with the indirect water heater. I have been told by many oil companies that a boiler with a domestic coil uses about 200 to 250 gallons (1 tank of oil) per year to make domestic hot water. If using 250 gallons per year it would cost about $825 just to make hot water. Buy a indirect water heater with a lifetime warranty that way you can use it in the future if you need to replace the boiler.