Viessmann 200 with Honeywell Evohome

[Lexden]

I would be grateful for some thoughts/advice. I am looking to replace an Ideal Classic FF280 boiler with 'S' Plan connections. HW is via an unvented 250L OSO cylinder. My property comprises 5 beds, 2 ensuite, a bathroom, and 21 radiators. The heating system is divided into 12 Evohome zones and all rads have HR92s. HW temperature is controlled via an Evohome HW kit wired in series with the existing tank stats. The Evohome controller controls 2 BDR 91s linked to the 2 mortised zone valves.

My 17 year old boiler is getting a bit creaky, and along with WB and ATAG, I am looking at the Viessmann 200 with an Opentherm connection to the Evohome controller. Any thoughts on my choice of boiler to work with my existing Honeywell system?

 

[Dan Robinson]

A 200 won't work direct with the OpenTherm bridge.

You should only have one zone valve.

 

[Lexden]

A 200 won't work direct with the OpenTherm bridge.

You should only have one zone valve.

Thanks - that's helpful.

 

[kittedup]

I'd keep that classic going if I were you.

One of the best boilers ever made.

Ted

 

[muggles]

Depends on your motivation here. If you're out to save money overall, chucking the Classic away isn't the way to do it - they're good solid boilers with readily available low-cost spares and reasonably efficient. If you want to use as little gas as possible, but lose a chunk of capital to achieve that, then a new boiler is the way to go (but neither WB nor the 200 will work with the Evohome OT bridge...not sure about ATAG...Intergas definitely works with it)

 

[Lexden]

Thanks all. i appreciate your thoughts.

 

[simond]

In terms of what works with OpenTherm; I'd advise you not to use it with Evohome. The benefits offered by OT are minimal anyway, in comparison to the savings Evo can deliver on its own.

 

[Lexden]

In terms of what works with OpenTherm; I'd advise you not to use it with Evohome. The benefits offered by OT are minimal anyway, in comparison to the savings Evo can deliver on its own.

What, if any, are the benefits of mixing Evohome and a boiler with weather compensation? I appreciate that it could be argued that Evohome zone optimisation and weather compensation are very much the same thing but with different solutions.

 

[RTFB]

None, really. Fit it with weather compensation, you can't do better, My Lord. Add TRVs, programmable if you wish.

 

[simond]

Evohome can save 30% of your energy bill. It can make your lounge warm in the evenings without boiling the rest of the house, and it can warm your bathroom towel rails in the summer.

Programmable TRVs can't do that because they can't turn the boiler on and off.

Compare a condensing boiler with/without weather comp and you'll be hard pushed to get a 5% uplift. It's not new and its not clever, boilers have had weather comp for decades (particularly commercials). But in commercial environments 5% is a lot of money and zoning isn't relevant because everything is heated en masse. The lights stay on everywhere too.

Domestic is different, there are normally far more rooms than occupants.

Turn your Viessmann stat down to 65C and the WC versus non WC will achieve almost no savings by comparison.

 

[Lexden]

Evohome can save 30% of your energy bill. It can make your lounge warm in the evenings without boiling the rest of the house, and it can warm your bathroom towel rails in the summer.

Programmable TRVs can't do that because they can't turn the boiler on and off.

Compare a condensing boiler with/without weather comp and you'll be hard pushed to get a 5% uplift. It's not new and its not clever, boilers have had weather comp for decades (particularly commercials). But in commercial environments 5% is a lot of money and zoning isn't relevant because everything is heated en masse. The lights stay on everywhere too.

Domestic is different, there are normally far more rooms than occupants.

Turn your Viessmann stat down to 65C and the WC versus non WC will achieve almost no savings by comparison.

Evohome replaced the conventional timer, hall stat and manual TRVs in my home and we are saving just under 20% per year in gas usage with the added advantage of heat when and where we want it. As each HR92 demands heat it does operate the zone valve and activate the boiler (that said, the zone valve could have been left in the open position). My installer just went for the simplest solution.

I suppose the question that I am asking is how best to integrate a new boiler into an existing Evohome with 'S' plan system? Noting your comments about WC, will this work with Evohome room optimisation: if it does, are there any measurable benefits or is it just more to go wrong? Evohome is a great system but it does require some knowledge if things go awry.

 

[simond]

Opentherm compatibility is an issue that adds complexity, some risk, for very little benefit.

 

[Lexden]

Opentherm compatibility is an issue that adds complexity, some risk, for very little benefit.

That's not how the guys at Honeywell UK see it but they would be in favour of it - wouldn't they.

 

[Mike_Sammon]

Either do the Viessmann 200 with weather compensation and Evohome not wired back to the boiler or do the Viessmann 100 or another decent open therm boiler with the open therm bridge.
Send me a message if you want more advice. Regards.

 

[Lexden]

Thanks Mike - I might just do that.