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Vitodens 200 - What size??

Charlie_11 Member Posts: 10
Thinfin plates under floor under hardwoods. In short- I was told the 6/24 is the one I needed. Temps under 120 I hope. Anyway, local contractor has a 8/32 he'll install for the same price. He admits it's overkill, but now I wonder if I'll be paying for too much down the road. Thanks


  • Charlie_11
    Charlie_11 Member Posts: 10
    Vidodens 200 - What size??

    Retrofit 1800 Sqft home. Would the 8/32 be too big and consume more gas and cycle through more on/off and end up costing me more in the end then the 6/24? Given my initial cost are about the same that is. Thanks, Charlie
  • grindog
    grindog Member Posts: 121
    heat loss calc

    Did you have a heatloss done?
    What type of heat do you have?
    A proper heat loss calc is the first step to sizing your boiler. If you are running any type of high temp heat you may not see the bennifits of a condensing boiler.
    Need more info to help you with your question.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Don't know your climate or construction of the house, but the 6-24 is MORE than adequate for my 1903, 3,400 sf home with lots of large windows, ridiculous number of doors to the outside and outside design temp of 8°. Boiler input is very close to my HVAC-Calc based heat loss. A few suggested I should use the 8-32. Glad I didn't as the 6-24 is, again, more than adequate.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    "Overkill" will result in a system that can't take full advantage of modulation as the boiler will be forced to operate digitally except in quite cold weather. If DHW production is part of the problem, use a higher capacity indirect as opposed to oversizing the boiler.
  • Charlie_11
    Charlie_11 Member Posts: 10
    so that . . .

    Thanks Mike. My layman’s understanding of this is that in our cold environment, the more modulating the more load on the system. Not to mention the additional fuel used. I hope that makes sense and is correct. I’m leaning toward the 6/24.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Am primarily "just" a homeowner like you...

    The Vitodens (and any modulating boiler for that matter) cannot modulate down to nothing.

    The 6-24 can modulate down to 22,000 btus per hour (6 kilowatts per hour); the 8-32 down to 33,000 btus per hour (8 kilowatts).

    With normal room temperature settings my 6-24 only begins to modulate when the temp drops to about 40°. (Make a mental comparison from the simple description I gave of the house.)

    Once installed, find the lowest possible reset curve (ratio especially) to maintain the lowest temperature you deem comfortable. Try 0.3 ratio and 0° shift. Set the sun dial at the warmest temp you want to maintain in the house. Make changes in small increments and only after at least 24 hours to stabilize--the closer you get to perfection the longer you should wait between any changes. The curve is fully accessible to the user and there are reasonable instructions in the user manual--it just seems best to start too low and work your way up gradually. For optimum efficiency you will need to increase the sun dial AND the thermostat(s) to increase space temperature above your desired maximum temp.

    Once you find your perfect curve, avoid adjusting either thermostats or the boiler.

    Adjusted this way, laugh at the gas company when the bill arrives and if you want to say "screw you" to the gas company, wear more clothing and turn the sun dial (and thermostats) down quite low.

    By maintaining my house 5-6°F lower than last year AND adjusting the curve in the manner described, I have reduced gas consumption by more than 50%!!!! This after having achieved about 43% savings when the boiler was installed last year. To be fair however, part of that 43% savings came at the end of last season when I began the curve adjustment. The curve was never high (141° supply temp at design) but the almost unbelievable savings this year are based on the original curve--not the slightly adjusted near the end of last season.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Sorry--had Warmboard in my head for some reason, not "thin-fin". Considering the max supply temp that's presumed the only change I'd suggest is starting with a 0.3 reset ratio instead of 0.2
  • Joel_3
    Joel_3 Member Posts: 166

    stick to your guns on the heat loss and go 6-24 . i have a great supplier up in Woburn and that's the only thing we but heads on they always try to sell me a bigger boiler it's hard to get them to stock a small one .We frequently put in boilers that are too big because I can't convince the customer not to . I just had a competitor bad mouth us on a job where I wanted to sell a 22 and he wanted a 33 . The house didn't even have enough radiation to support a 33 and we all know most houses are over radiated anyhow . i even tell people I'll put in writing it will work and I'll remove it at my exspense if it doesn't . " nope give me a bigger one" sigh.....

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