2700sq ft, 3 Zones, Weather Comp & OpenTherm

[Ambergold]

Hi all,

 

I have a 2700 sq ft house over three floors, currently using 2 x 26KW 20 year old non condensing system (H + HW) boilers and 300L HW tank w zoned floors controlled by 3 nests. 

Getting massive Gas Bills, have insulated as much as possible and now replacing both boilers for a Viessman 100W as don’t think the house is airtight enough for a heat pump.

 

I want to use OpenTherm but can’t do three Zones apparently.

 

I’m considering opening up the house to 1 large zone and using weather compensation. Happy enough to rip out the Nests or go for a different boiler option.

Can anyone give me a steer on how best to design this? The plumber is proposing leaving the current nest setup but we hate the hot / cold, on / off system we currently have.

 

Thanks……

Edited March 1, 2023 by Ambergold

[JohnMo]

If you have Viessmann boiler use their controller. If your plumber is not comfortable with doing how Viessmann design their system, get another plumber who is.

 

On weather compensation you should be getting on average over 100% efficiency out of the boiler, your none condensing one was possibly 60 to 70%.  Keep the flow temps as low as possible.

 

Make sure your plumber doesn't plumb as a normal Y or S plan, you need it set to priority hot water or X plan, this allows the boiler to heat the cylinder at a high temp and heating system on a low temp or weather compensation.

[Ambergold]

Thanks

[HughF]

Urban Plumbers on YouTube does this sort of conversion/upgrade all the time. Worth seeing if he covers your area.

[Ambergold]

On 02/03/2023 at 17:26, HughF said:

Urban Plumbers on YouTube does this sort of conversion/upgrade all the time. Worth seeing if he covers your area.

I’m in a different country but I’ve watched a lot of his videos over the last two

months. Impressive operator!