Renovation - conversion to low temperature heating

[Church of Noise]

Dear all,

The GF & I bought a 1958 house and are having it renovated.

We decided early on to have underfloor heating downstairs, yet on the first floor, this is not possible.
An additional bit of info is that we decided to use the Honeywell Evohome system.

First idea was to have two separate circuits, one for the UFH (low temp) and one for the radiators on the first floor ('high' temp, as it was). This brings some practical things to consider, and we decided to either go for

• a solution with a gas boiler that can run two separate circuits (http://www.ithodaalderop.be/producten/cv-ketels/cube-duo/ in Dutch, sorry). Downside here is that the Evohome can't communicate using Opentherm with this system, which would mean it would only work on/off, not modulatingly.
• the replacement of all radiators, so the entire installation is converted to low temperature heating. Downside of this obviously is the additional cost for 4 radiators (bath room + 3 bed rooms). Upside is that we have quite a range of boilers to choose from.

What solution would you suggest?

Thanks!

[Church of Noise]

Gingerbread Man said:

Why can't you run under floor heating upstairs? It's possible.

Any boiler can run the two zones via zone valves.

Fair point, however we are not tackling the first floor yet (largely because of the available budget).

Agreed that the investment for the new radiators is not very large relatively speaking... Yet at a certain point in time, one needs to keep an eye on total spend,hence the question.

[Church of Noise]

Thanks for the valuable input!

One more question: the guy who's going to install the heating system said that by defining a zone for each room could cause problems: when only one room with a radiator needs to cover a (limited) temperature drop, the boiler would generate too much power (because it can't be modulated between 0% and 100%) and as such cause for quite the loss in efficiency. This however contradicts some users' very positive experience with the system.

Does anyone have a view on this please?

[Church of Noise]

Gingerbread Man, Pheo,

Thanks for your views.
You more or less confirm what I was thinking, and I shall probably have a limited number of zones (ground floor and first floor) to avoid the issue Pheo described, the other radiators at the first floor can then remain 'normal' ones. They're only for the bedrooms anyway.