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Upgrading oil fired hydronic system in stages...

Hi all, I was hoping you could give me some input in to my plans for upgrading my current hydronic system. I'd like to do the upgrades in two stages and I want to make sure I'm not missing anything.

The house: Ranch with a walk-out basement in upstate New York. Approximately 2,225 sq ft of conditioned space. 55k Btu/h per heat loss calc. The house was in good shape when I bought it, but very outdated. I'm in the process of gutting and finishing the basement right now so I have access to basement ceiling space to run new piping.

The existing system: Buderus G115/28 oil fired boiler with Riello BF3 burner installed in 1996. 113 mbh in, 98 mbh out. Taco system circulator with (3) zones controlled by zone valves. 1 zone for a 30 gallon indirect DHW tank, 1 zone for baseboard fin radiation upstairs, and 1 zone for baseboard fin radiation in the basement. The boiler seems to be in good shape per the latest servicing, but the near boiler piping is a bit of a rat's nest. The fin radiation cover and fins are pretty beat up. The fin radiation is a one pipe system that is piped in series. Ugh. The rooms at the end of the loop are much colder than the rest of the house and unfortunately one of them is the baby's room. We have an electric space heater in there to keep the temperature up. No DHW priority, so we have problems with showers on cold mornings.

Where I'd like to go: High efficiency modulating, condensing gas fired boiler. Panel radiators (Myson or Buderus) with TRVs. One zone for upstairs and one zone for the finished basement. Constant circulation with outdoor reset and warm weather shutdown.

The reason that I'd like to accomplish this in stages is because I do not have nat gas to my house. I'm about 700 feet from the gas main at the street and I was quoted $3,500 from the gas company just to run the line to a meter outside my house. Add that on to the cost of a new boiler, installation and gas piping inside the house and that's quite a bill. Since I have a working boiler right now I'd like to get the house ready for the day when the gas and boiler replacement come. I recently redid the domestic water plumbing in the house after moving the kitchen and adding a bathroom in the basement. I used Uponor's ProPex for that so I'd like to do the same with the heating. I would pipe all of the near-boiler stuff with copper to an Uponor manifold and then hePex everywhere else.

So for phase one I'm planning on installing all of the panel radiators in a two pipe system and redoing the near-boiler piping. I'd size the panel radiators for 160F or 140F entering water in anticipation of the future condensing boiler. I'll use a Tekmar 260 controller with a DHW circ pump for DHW priority and a Taco Viridian delta P circulator for the two panel radiator zones. If I tap the DHW hot water inlet piping off before the Viridian circulator I believe I can use the Tekmar 260 to send 180 to the DHW when under priority and 140 or 160 to the radiant panels. I would like to use an Uponor 2-zone EP radiant manifold for the panel radiator loops. This is where I'd switch to pex. I'd use thermostats and Uponor manifold actuators to close the supply to the zones and provide scheduled setback.

One thing I'm not sure of is the allowable return water temperature on my Buderus G115. I thought I had read that these boilers can handle a lower return water temperature, but I don't have a manual that gives any actual numbers.

What am I missing with this? Does my plan have a lot of holes in it? I'd really like to hear any input or suggestions you might have!


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    You could just pipe in a bypass with a thermostatic mixing valve. But you're boiler will probably now short cycle.
    Something like this:
    Or even a 4 way valve.
    I think you're supply temps for panel rads may be too high, but your room by room heat loss will tell you what size.

    There was an error rendering this rich post.

    EBEBRATT-Ed Member Posts: 15,764
    Your plan makes perfect sense to me. If the calculations show that your anticipated return water temperature is too low as @STEVEusaPA stated you can easily use a mixing valve. This will allow you to run the boiler at a warmer temperature than the your new radiation until the new boiler is installed
  • elrefresco
    elrefresco Member Posts: 2
    Thanks for the replies. Would something like the attached schematic work? This uses (2) 3-way thermostatic mixing valves. This seems like a simple way to protect the boiler and provide something like 140 (or even 120?) to the radiant panels.
    EBEBRATT-Ed Member Posts: 15,764
    That's fine
    HVACNUT Member Posts: 5,875
    I wouldn't spend $3,500 for a Nat. gas line. Think about LP? Also the G115 is able to handle low return temps with its 1" return entering the bottom of the boiler, and it's specified in their literature. You can download manuals at Buderususa.com.
    What is your current aquastat? The Buderus 2107 Logamatic has the capabilities to do everything you mentioned. I'm partial to oil for some dumb reason.