Setting the max output (input) of a Viessmann Vitodens 100 with Combi-plus

fleishman

Hi all!

I just installed a new 100-W 35KW mod/con with a combi-plus dhw and low loss header running nat gas.

Currently heating 900 sq ft ranch (future second zone will heat 900 sq ft basement).

I am curious on how to properly set the max input modulation for maximum efficiency. I followed the set up instructions and set the % of max input to 6 on the 1-6 dial range assuming I'll need all the btus I can get in the winter. The boiler runs at ~165 max boiler temp and mods down to about 1 bar of flame; the house heats up just fine.

Instructions: http://www.viessmann-us.com/content/dam/internet-ca/pdfs/doc/cpk/vitodens_100-wb1bc_is.pdf page 65

I do not have a flue gas analyzer to test the range at max input and min input.

I did not install the outdoor air temp sensor as I was instructed it could not be used with the combi-plus attachment.

Do I want the temp to reach 180 degrees for my radiators to heat most efficiently? Or, is the boiler reading the return water temp and setting the water temp at the most efficient level automatically?

Winter in Maine; the average temp outside is 20-30 degrees F during the heating season.

Thanks!

Tim McElwain

If I am not mistaken that boiler only goes as high as 165 degrees. I do not have the manual in front of me. I would suggest having someone with a combustion analyzer check out the boiler.

GW

Look at page 79, it will go to 178. I've installed dozens of these units, only held by breath once where I needed a bit more temp. Good little boiler. I have not installed the heat exchanger though.

Gary

CMadatMe

The dial setting has nothing to do with the modulation % but rather the heating curve. So at 6. You'll get the full 176 degree water temp at 41 degrees outside. Not ideal. You'll rarely be condensing and getting the fuel saving benefits. You're more likely only going to get 88-90% AFUE at those high water temps.

Robert O'Brien

fleishman said:

Hi all!



I do not have a flue gas analyzer to test the range at max input and min input.
Not a good idea!




I did not install the outdoor air temp sensor as I was instructed it could not be used with the combi-plus attachment.

Not true!

Robert O'Brien

With 900 sq/ft you'll never need more than the 37K min input except on DHW

CMadatMe

Didn't catch that he didn't use the ODS.. Another bad move.