Gv90+5

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Ghynes440
Ghynes440 Posts: 68
in Gas Heating

we had a new unit put in last year when we switched to gas, we live in an older 1800s home with poor insulation and cast-iron hot water radiators.


What is the recommended boiler temp setting for something like that with our home? Last year I the boiler at minimum efficiency setting and it seemed like our boiler kicked on and off all the time and our gas bill was rather high each month in the winter.


So this year, I’m going to try the max efficiency setting on the boiler to see if that helps, but I’m trying to figure out the best boiler temp setting to set it up. By the time our radiators get heated up, most of them are around 105 to 110°.

Comments

  • HVACNUT
    HVACNUT Posts: 7,759

    Those boilers are notoriously piped incorrectly.

    Screenshot_20261007_173837_ProTools.jpg

    If zoning with zone valves, no external circulator is needed. If zoning with circulators, primary/secondary piping is required.

    The boiler temperature setting is just a safety. Ideally it'll set where the boiler runs continuously on the coldest day of the year while maintaining the indoor set temperature. The 5 has a net rating of 113K BTU's. Do you know the square footage of the heated space and the design day temperature for your area? Because that boiler should be large enough for a cold climate 4,000 sq ft house.

    Can you post pics of the boiler and connected piping?

  • Ghynes440
    Ghynes440 Posts: 68

    it’s a 2600 sqft house and the design temperature is around 14 degrees.

    IMG_2114.jpeg IMG_2115.jpeg IMG_2116.jpeg IMG_2117.jpeg
  • hot_rod
    hot_rod Posts: 28,606

    You have it piped as the manual shows with a primary secondary close tees.

    Screenshot 2026-10-07 at 5.00.04 PM.png

    I think your system with CI rads and large piping could have been piped direct, omit the zone valves shown.

    Screenshot 2026-10-07 at 5.00.16 PM.png

    As @HVACNUT mentioned, you need to do some calculations to assure the correct piping.

    Direct piping may be nore efficient as cool return comes directly to the boiler, increases efficiency. The P/S you have does some blending.

    The boiler modulates, if the control is set properly I wouldn't expect short cycling?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ghynes440
    Ghynes440 Posts: 68
    https://forum.heatinghelp.com/discussion/comment/1905736#Comment_1905736

    does it matter if our home is set on one zone?

  • hot_rod
    hot_rod Posts: 28,606

    I misspoke, that is not a modulating boiler, I was think an Ultra. The GV5 is about a 113,000 btu/hr output.

    So you are correct, with just one zone running the boiler will probably cycle frequently. If you calculated the radiator size on the smallest zone you could see how close to 113K the radiators can transfer. With that you could calculate that run time.

    Easier yet set up a chair next to the boiler and time that small zone- boiler firing time. Mild early season, low load days will present the worst short cycle condition.

    This is the downside of a fixed output boiler on zoned systems. Short run cycles can drive an 85% boiler into the 70% efficiency range :(

    In a perfect world on the coldest day, all radiators running the boiler would run non stop, adding the amount of heat energy as the building losses.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HVACNUT
    HVACNUT Posts: 7,759

    It looks like one thermostat in the house? It was piped P/S, but with one zone it could've been piped straight in and out (with no external circulator) like @hot_rod said. That would bring cold water directly back to the boiler for longer cycles before it makes limit. Max out the economy setting.

    I cant answer for the heat loss on a 19th century house, but almost 43.5 BTU's per sq ft is a lot anywhere.

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