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Viessmann 200W heat curve questions

Tonerlow Member Posts: 60
We have a 199000 BTU Veissmann 200W providing in floor heat to a 6500 square foot shop in SK Canada. Attached to the shop is a small lean-to which contains the boiler, pressure washer air compressor etc.

There is no in floor piping in this boiler room, as it was poured after the main shop. We have had ongoing problems with keeping it warm (frozen pressure washer lines etc.) Right now we have a Reznor air handler installed, but it is only able to draw the same supply temp as the in floor heat, due to not having as mixing valve installed and the boiler programming does not recognize the 2 separate heat calls. We are not seeing any benefit from the unit heater at the current supply temps

I know the correct answer is to get a mixing valve, and coding changes on the boiler to perform both functions properly.

My question is 2-fold

1> What is the max supply temp before we will damage the slab (140F??). Can I just turn up the SHIFT on the heating curve to provide a higher supply temp to both the slab and the unit heater? (Making sure to not exceed the max safe supply level on our coldest days)

Currently the heat curve shows setpoints of 0C ambient =13C supply -10C= 22C supply -20C = 30 C supply (presumably -40C=41-42C supply?)
It gets as cold as -40C ambient temp here, MAYBE -42C
Slope is .9 right now and shift =0

2> If the answer is yes to question one, then what kind of efficiency is being sacrificed as the set point increases?


  • GGross
    GGross Member Posts: 933
    You could turn up the supply temp, 140 would be the absolute maximum I would go, and even then that may not be good for your floor. Have you considered a medium/low temp radiator in the mechanical space piped as a separate zone? Is the space insulated? Most 200 series boiler that I am aware of, and certainly all of them sold here in the last 5-8 years or so will take up to 3 separate calls for heat each with their own temperature, it will only be able to fire at the highest currently calling of course. I think the solution is either electric baseboard in that space, or a mixing valve for the infloor and 2 calls for heat with different curves
  • Tonerlow
    Tonerlow Member Posts: 60
    Yes we have it insulated and have eliminated most of the draft by adding another interior wall. Our long term plan is to get a mixing valve installed and coding upgrades to be able and utilize the air handler we have in there already (paid 3000$ for this a couple of years back). I wonder if a low temp radiator would plumb in place of the one we have now. That would be another option.