Viessmann Vitodens 200 Combi Boiler?

SpeyFitter

I have yet to install a Viessmann boiler in the field, but there is a local Viessmann plant that offers Academy sessions which I plan to take this fall, however I've installed a few other brands of Mod-Cons - mostly IBC's, which are made in Vancouver, as well a a few electrics, and other gas boilers.

I might be buying my mom's house potentially which is a 3 bed/1 bath rancher, about 1100-1200 square feet potentially, with a crawl space and I'd like to retrofit radiant floors into it in the joist spaces (coined as "staple ups," but I'd use the Radaint Heat Transfer Plates by Rehau more than likely). The house currently has about a one year old Bradford White 40 gallon electric lowboy, but I'm sure I could find a new home for it.

I had an earlier idea to go with a simple Thermolec electric boiler for this application. But one night recently I decided to crunch the numbers with eletricity versus gas and suffice to say even with the 3rd lowest electricity rates in North America where I live, it's still pricey to heat with electricity.

Currently where I live it's $9.78 per gigajoule (950,000 BTU's) for gas, about $16.43 per gigajoule of electricity, and if you use over 1350 kilowatts every 2 monthes, you are charged $23.00 per gigajoule for every KW over that amount (one Gigajoule = 278 kilowatts roughly). So it's 1.6 to 2.3 times as much to heat with electricity if you assume 100% efficiency with both appliances, which is not the case, as most electrics are 100% but most mod-cons are 92-95% AFUE - with even higher efficiencies in low temps. But in a nutshell it almost makes some heat pumps not seem worth it, at least a air to water version, on colder days.

So I've dreamt up another solution - Viessmann makes a combi boiler which has a plate heat exchaner built in that modulates from 25,000 to 90,000-ish BTU's. The Boiler acts as both a boiler with a boiler supply/return, and a tankless (sort of) with the cold in/hot out through the brazed plate heat exchanger. According to the Viessmann specs, it will produce 2.1 GPM's at 128 degrees and that's with a 50 degree cold water inlet temp, which is reasonable for a 3 bed/1 bath rancher, but I have dreamt up another idea:

What if I did a Solar Domestic preheat tank upstream of the boiler, which would bring up the inlet temp of the domestic water fed to be heated by the boiler? This would in effect increase it's output and save $$$ obviously.

So I'm curious of a few things

1) What can you tell me about this particular Viessmann model if you've installed it?

2) Any thoughts about the set up I described?

3) Any Input on the Viessmann Vitodens 100, which is about half the price, which I could use with an indirect tank

scott markle_2

vito 200

I have installed a couple of combi units for happy customers. If you want a drenching really hot shower and you have cold supply water you may find it a it a bit inadequate.

The other issue that I have had to deal with concerns short cycle in low load low temperature applications. The burner is designed for lots of short on/off operation as it must be for instantaneous dhw, but the little pulse burns that are required to meet the low supply target temps in small radiant applications bothers me. There is no differential adjustment so working with the native control there is very little that can be done. The other thing about the 200 is that it utilizes a step up transformer to run the boiler at it's euro 230/ 50 hz. power requirement, the power consumption from the variable speed pump is not terribly impressive, I assume because of losses in this step up transformer arrangement.

The vito 100 has no biltin circ., a less fancy burner, no built in reset control, but basicly the same heat exchanger. It can be easily interfaced with third party controls that use a 0-10v control signal, like a tekmar 270