Hi,
Our house is arranged over 3 floors and the current system has a zone valve for each floor, all 22 radiators have manual TRVs. For various reasons the old control system must be replaced (long story). The boiler is a large traditional open flue boiler (not condensing), hot water is an unvented cylinder on a separate time clock.
Right now some rooms remain cold even when the thermostat thinks the house is up to temperature (it's an old stone house with little scope for extra insulation and we're not going to replace any radiators). I think it's due to poor placement of the thermostats rather than an unbalanced system or undersized rads.
The honeywell HR80 wireless radiator TRVs with their CM-Zone or EvoHome controllers looked interesting as an option but fitting one to each radiator in the house would be very expensive, cheapest I found the HR80 is £75 so £1650 for the whole house!
Would extra zoning/room scheduling really save that much extra (enough to justify all the HR80s) over the 3 zone control we currently have? Particularly for the first and second floor which just have bedrooms & bathrooms - individual rooms (eg spare room) that are not in use can already be turned down via their TRV. Whilst it would be nice to have separate control of the the bathroom temperatures, I can't justify nearly that much expenditure to achieve it.
Instead I'm considering using either the evotouch: or three cm927 programmable stat units: to control the 3 heating zones via the existing zone valves. If necessary I could still add a couple of HR80s to act as remote sensors in the rooms that don't get hot enough under the current system or just move the wireless stats from the hallway into those rooms.
The price breakdown (without HR80s) is as follows:
With EvoHome - [*] evotouch controller with one relay: £251 [*] Two DT92 sensors/setpoint adjusters - £65 each [*] extra relay for boiler control - £60
Total cost £441.
With CM927 - [*] 3 x CM927 stat & relay packs: £102 each [*]One extra relay for boiler control £60
Total cost £366.
The CM927 option is cheaper but I won't get the snazzy touch screen central control, or the flexibility to later add extra zones by filling the house with HR80 TRVs (evotouch supports up to 8 zones). Right now I'm leaning towards the evotouch.
I believe that when a boiler relay is fitted both stats performs load compensation by cycling the boiler, dependant on how close to the set point it is and how fast the house is loosing heat. Can anyone verify this?
Is a direct load compensation like this right for a conventional open flue boiler? The Honeywell pages say the CM927 & evotouch are for any boiler but I read some worrying things about direct load compensation resulting in condensate corroding the heat transfer matrix when used with non condensing boilers.
I'd get a gas safe man in to do the install (unfortunately all the domestic installers I've contacted so far have been rubbish at giving advice) but once it's in adding extra wireless TRVS should be a DIY job.
Any comments or suggestions would be much appreciated. Should I be considering any other systems? I've also looked at heatmiser: but to me it didn't to seen as good as the honeywell options.
kind regards,
drbob