# Qs how stat on oil boiler and wall stat in house relate and more...



## Passport1 (22 Dec 2010)

Hi
I have oil central heating system running a FireBrid Enviromax boiler that is in a boiler house external to the main dwelling with pipes running back to the main dwelling

It has been suggested to me so that to ensure pipes dont freeze in this really cold weather to have the heating system timer set to run all the time or at least during the night and to turn the stat on the firebird boiler down to the minimum setting as low as it can go and have either the water or the heating set on constant on the timer in the house

I have no problem doing this as dont want frozen pipes or worse

Im just wondering 

1. What is the relationship between the stat on the boiler itself and the stat in the dwelling house

2. If i have the stat on the boiler turned down as low as it can go say over night and the heating timer set to be on all the time, what setting should i have the stat inside in the house set to - do i need to have it at 20 degrees or would it be ok to have it at 18 or 16 or lower degrees

3. Is there any recommenation regarding if temperatures hit a certain minus value that you should leave your heating running all night on a low setting or have timer set so that heating comes on for a while a few times during the course of the night

4. Also what is the most efficient setting to have the stat on the boiler set too. Up until this time, I would never have gone near it seems to be set near to the max setting it can be set too - maybe set at 80-90%. In normal weather conditions what would be most efficient setting to have it set to and also the internal wall stat in the house 

5. Also if out of the house for periods of time over the christmas e.g. away for couple days and have heating timed to come on at different times of the day - how long each time heating comes on is it recommened to time it to stay on - 30 mins, 1 hour, longer... so as dont end up with burst pipes
Thanks
Sorry for all the questions


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## infacta (22 Dec 2010)

1. None. Boiler stat measures temp of water being heated while house stat measures air temp in the room. They each have a job to do but are not connected to each other. Boiler water temp starts about 60/65C while room temp should be about 20C.

2. As low as you like but not too low, say 10C. Whatever feels comfortable.

3. Depends on your control system. Modern ones will have a minimum setting on the stats and will switch on the boiler on if the house is in danger of freezing regardless on on/off time window.

4. This is a "tuning" exercise. If you are unsure get advice from a good plumber.

5. Again depends on a number of variables including weather. If in doubt make sure you run at regular intervals thoughout 24 hours.


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## Shane007 (5 Jan 2011)

1. As Infacta states.
2. Turning down the boiler stat will cause the boiler to "short cycle". It will reach the low temp quite quickly and stat out (turn off) and when temp within boiler jacket cools below set temp, the boiler will re-start. Short cylcing uses a lot of oil. Boilers are designed to chase heat rather than the above. You are better to set the boiler to come on say once an hour for say 15 mins. Otherwise fit a frost stat in conjunction with a pipe stat. Turning down the room stat inside is as Infacta states.
3. As above.
4. The numbers on a boiler stat are not a percentage but a temperature. The most efficient setting is between 70C and 75C. For non-condensing boilers, you want to balance the system to give you a 20C temperature difference between the boiler flow and the boiler return. For condensing boilers, you want a temp difference of 10C. You can also do this be fitting a thermostatic valve between the flow and return set to 50C with the flow temp set to 70C. Internal design room temperatures are generally 21C and 22C for bathrooms. Higher for elderly people.
5. Again with a frost stat fitted along with a pipe stat, you do not have to worry about temp drops as the frost stat will have a permanent live to it, independent from your timeclock. The pipestat should be set to 30C to turn off the boiler when the water temp reaches 30C. The frost stat will kick in at 4C. It's not an expensive job either.


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