How to wire frost stat to two zones? Where to put it?

[David Robinson]

Now that I've gone mad and introduced a separate heating zone, how do I wire a frost-stat in?

If I just connect it to both valves, then both will be forever linked, and they'll be no point having two. If I connect it to only one of them, then the pipework hanging off the other will never get warmed.

Do I need to get the frost stat to switch a relay with two connectors or something? I can't find anything like that in the usual places, but then I don't know what to look for!

Alternatively, are there frost stats with two separate outputs? Then there'd be no problem AFAICT.

We've never had a frost stat before, but it seems a waste to leave the heating on when we go away - and the weather we're having at the moment, I can imagine it might be needed in the middle of a normal night!

Any hints on the best positioning for a frost stat also gratefully received.

Cheers, David.

[dennis]

There is no reason why you can't have two or more frost stats. I have one in the conservatory and one in the house. The conservatory one bypasses the timer stat that normally operates the fan heating. The other bypasses the timer stat in the lounge.

[ARWadsworth]

You might not need a frost stat. They usually only needed when the boiler is in an unheated place such as a garage.

I just leave my heating on constant and turn my room stat down to about 5 deg if I leave the house in winter.

[Colin Stamp]

What type of room thermostat do you have on the original system? Since you're getting a programmable one for the conservatory, it makes sense to have one on the original system too. Then the original timer becomes redundant, set to 24H, and you have automatic frost protection from the room stats.

Cheers,

Colin.

[David Robinson]

While that sounds sensible in theory, in practice that's going to confuse some people in the house ;-) So I'm sticking with programme + dumb roomstat for the main house for now.

I guess one pipe stat + two frost stats would do?

I know I could just leave the heating on with the main roomstat turned down, but I can just about imagine the low temperatures coming when the programmer is off. I'm guessing it's the pipes under the floor which would freeze first, despite insulation?

It's North Yorkshire tha knows! We got -7 last year!

Cheers, David.

[ARWadsworth]

Doesn't your new thermostat for the conservatory already act as a frost stat?

[David Robinson]

Don't know yet, but I think that goes down to 5 degrees C. I don't think I want the heating on all the time the conservatory is at 4 degrees - that'll be every two hours every night for much of the winter! I was hoping a frost stat could go lower before switching on, and then be switched off once the pipes (rather than the rooms) were hot.

But maybe I'm over thinking it. Maybe it doesn't really matter.

Cheers, David.

[ARWadsworth]

I doubt it will be below 4 deg for two hours a night inside your conservatory!

Frost stats are used in two ways.

The first way is used when the boiler is in a place that is not heated such as a loft or garage. When a frost stat is used here then a pipe stat is also needed on the return pipework and wired in series with the frost stat to turn the heating off when the pipes are hot. The idea is that the frost stat calls for heat and the boiler fires up, heats the pipework in the unheated area and the pipestat then shuts the heating down. As the frost stat receives no heat due to the boiler firing up the secondary stat (the pipe stat) is needed as the frost stat could be calling for heat all night.

The second way to use a frost stat is where it is going to receive heat by turning the boiler on. Your conservatory is a prime example. If the conservatory air temperature drops to 4 deg then the boiler fires up and the consevatory heats up. When the conservatory reaches 6 deg the boiler turns off. You could always do this with your house by turning the heating onto constant and turning the house thermostat down to 5 deg if you are leaving the house empty for several days.

Cheers

[David Robinson]

Thanks for the explanation Adam.

In that case a separate frost stat seems overkill here. Good. That saves me a job!

Cheers, David.

[ARWadsworth]

It will be interesting to see how your conservatory stat behaves if we have another cold winter.