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Out with the oil and in with the gas. Which boiler?

bio_guy Member Posts: 73
My dad has proposals from three contractors for oil-fired boiler conversion to gas. He is not seriously considering two offers from these contractors to replace the oil burner with a gas burner and leave the 55 YO Crane Sunnyday in place. That old soldier, in case you are not familiar, provides heat and DHW (with a coil). He is alone in the house most of the time with weekend and vacation time family visitors. He is in central NY. (There are lots of heating degree days there.) There are fin-tube radiators in three zones, one very small.

Two contractors proposed a Weil-Mcclain GV90+ Neither of these included an outdoor control. They are probably correct in their conclusion that dad will not live long enough to pay back the price in energy savings for that option. Are there other advantages to that kind of control that should be considered?

One with a PurPro 40 indirect water heater (Pro41Z140)
The other one with a Bradford White PowerStor 30 gallon indirect.

One of the above contractors also proposed a Baxi DuoTec (BAXLUNADUOTEC40KIT). Again, no outdoor reset.

A third contractor proposed a Rinnai E110C. Apparently, this comes with a outdoor reset as standard equipment.

I know that the combination boilers will not provide hot water as fast as the indirect heaters. I hope that they will match what he has now. There are some price differences, and there are differences in what will be done with the existing oil in the tank, buy back or give away.

What I’d like are some comments on the operational differences in these boilers. (I see that the Baxi is a 7:1 whereas the Rinnai is 5:1.) In addition to that, any comments about reliability would be nice and any input about installation complications. I am having a hard time comparing the DHW output of the modulating boilers. The Baxi literature says that will make 3.9 gpm but give not temp differential to go with that. The Rinnai says 3.2 gpm at 75F delta.

There are things that I do not understand about the boilers. How are the Rinnai and Baxi able to handle a constant flow-through of oxygenated water while the Weil Mcclain is not? Is there a minimum water flow to activate water heating with these combination boilers? Does space heating output drop when DHW is made? The Rinnai installer says that he can go out the side of the house with flue gas, but the others say that they need to put pipe up the existing chimney due to window locations. Is there a difference with the Rinnai that dictates this?

Thanks for reading


  • Hello bio-guy:
    The Rinnai and Baxi units that the contractors proposed are combi units; they have a heat exchanger inside for domestic hot water (DHW) and all components are non-ferrous and are OK for potable, oxygenated water. The Weil-McLain is a heating only boiler and has a cast iron heat exchanger that is not compatible with oxygenated water.
    I don't know if there is a minimum flow requirement to turn on hot water as with "on-demand" water heaters, but my guess is no.
    Most of the new boilers have priority DHW production, that is, heating is turned off while there is a call for DHW. Hot water for domestic use is more important; space heating can wait and you really can't tell that your space heating has been turned off, it's for such a short time.
    As far as the flue termination and distance to operable windows or other openings into the house, you have too look at the boiler installation instructions.
    You don't ask for boiler recommendations, but I will volunteer my own preferences which are Triangle Tube and Viessmann. Both have combi boilers that are excellent.

    Often wrong, never in doubt.
  • bio_guy
    bio_guy Member Posts: 73
    Thanks Alan, This is small town stuff, seriously small town. The downside might be that since everyone has preferences in the equipment that they like to install, my choices might be limited by that. On the upside, there is a lot of accountability. All three contractors are well known to us.

    Do you feel that the Triangle Tube and Viessman boilers are better quality in some way than the others or do you like some operational characteristics better, perhaps?