CU3A Low-Loss Header?

DC123

For those who have installed the vitocrossal 300, what are your thoughts about the need for a low-loss header? Any hits to efficiency? The argument made by the contractor was that it is particularly helpful with removing ferrous debris that may cause problems with ECM pumps.

DC123

Additionally, would be curious about your thoughts regarding the suitability of the CU3A26 for a house with an estimated design day (15F) heat loss of 45-50k and with two zones of fin tube (70ft and 50ft, total 120ft). Would the smallest vitodens 200 make more sense or would the high mass of the CU3A make this one reasonable?

EBEBRATT-Ed

You can make your own lo loss header for probably less than what Viessmann will charge

Solid_Fuel_Man

Vie$$mann

The cu3a looks like a very well made and thought out heat exchanger design. Why not do a magnetic dirt separator and not compromise on return temp?

Taylor

DC123

Thanks, I'll discuss with him. Any thoughts on whether the cu3a is appropriate for the heat loss and zone sizes I mentioned?

SWEI

The minimum firing rate on the CU3A-26 is 19k. I probably wouldn't use a LLH on it, given the design.

A 200W B2HB-19 (minimum firing rate 12k) better fits your heat loss. It is more likely to need a LLH or a hydro separator, but not always. A competent installer or designer will know how to decide.

DC123

Thanks. The attractive features of the CU3A are the ability to pipe direct and that it seems like it may be more reliable (but who knows) based on the design of the heat exchanger. Would be curious what the experience of folks who have installed a few of these has been, particularly in comparison to the 200W.

Paul Pollets

If the required flow rate is is under 6.5gpm, the LLH isn't required on the Vitodens 200. The CU3A seems a little much unless the BB load will lork well in the condensing mode.

DC123

Thanks. What has been your impression of the reliability of the 200 series? Are they finicky about maintenance like the giannonis?

Paul Pollets

Very stable control platform. Only boilers that come with "smart" modulating gas valves. They do need to be cleaned every 12-16 months.

DC123

Given the above load (45k btu at 15F, smallest zone is 50 ft of fin tube) and the option for either the B2HB-19 or the KHN-085 at the same cost, which would you choose? Either would be piped using a low loss header and the installer is equally comfortable with the support for either. Thanks!

DC123

Related question: assuming the Veissmann, what do you like to use as the primary boiler pump? The manual only mentions the 15-58, 0015, or Wilo S21, but presumably an ECM pump would save quite a bit of electricity.

Paul Pollets

I use either the 15-58 or the Grundfos Alpha. The boiler pump between the boiler and LLH would need to be the 15-58 on high speed.

DC123

High speed for the alpha too? It looks like the VR1816 could potentially accomplish it on medium and save a few watts - thoughts?

DC123

Looks like the vitodens 300W in Europe is already at 10:1 modulation. Pity that it's not available here yet.

Paul Pollets

When N. American heating contractors start insulating their piping, Viessmann will ship the 300W...LOL

DC123

Have you tried it with a VT2218? Or would that screw up the internal logic of the temperature sensing function it already has?

Gordy

Wouldn't do it.

Paul Pollets

Nor would I. The delta P pump works well when telestats or zone valves are used on the heating circuit.

DC123

Great, thanks both. One more question about the CU3A - do you still add a magnetic dirt separator? The company claims that all the debris drops out at the bottom of the heat exchanger, but I'm worried that ferrous debris would still clog up an ECM pump.

hot_rod

I would highly recommend a dirt removal device that includes a magnetic function with any ECM circulator. It doesn't add that much to the cost. Cheaper than a replacement pump

Here are some pics of ECM circs from barrier tube systems, one is our building in Milwaukee Kitec tube stainless boilers!
3rd failed pump in 14 years.

Pump manufacturers are making efforts to minimize that magnetite attraction, but a magnetic separator collects any particles out of harms way.

im

DC123

So I did a little research with Google Translate and it looks like there is a 7:1 turndown model of the CU3A available in Germany that modulates down to 8500 btu/hr. This seems like it may be an ideal machine for almost all scenarios with a medium-sized house. Has anyone heard anything about their making this model available in the US in the near future?

DC123

As a side note, Viessmanns look awfully cheap over there: https://www.meinhausshop.de/VIESSMANN-Vitocrossal-300-Gas-Brennwertkessel-ab-13-kW-mit-Vitotronic-200-Typ-KW6B

DC123

FYI: Just contacted Viessmann - they said no plans to bring over the 7:1 modulating model. Too bad! Really seems like it would be a terrific boiler to have available.