Multiple thermostats possible?

andre_xs

Hi,
we just bought a house and were wondering whether we could have 3 thermostats installed (living room and one in each bedroom) which are connected in a kind of "OR"-setting. In other words, as soon as one of the thermostats says "heating on", the heating goes on.

The heating in the house is ~10 years old, central gas boiler for heating and warm water (no warm water tank). Presently there is only one thermostat which is in the hallway.

The reason is that currently we sometimes have the awkward situation (with only one thermostat in the living room) to heat up the childrens' bedrooms, we sometimes need to make it very warm in the living room for the heating to go on in the first place...

The system doesn't need to be perfect, it should just e.g. turn the heating on when in the children's bedroom the temperature drops below let's say 20 degree, although we may have 21 degree in the living room. (It doesn't need to detect impossiblities, e.g. if the radiators are turned off with their own knob-thermostats, the heating would run forever...).

Edit: It should be as inexpensive as possible, because we are pretty short of money by buying that house...

Best wishes,
Andre

martinthebandit

TRV's would seem to be what you want

HappyMJ

Another vote for TRV's.

Bedrooms are supposed to be heated to 18 degrees at the same time that living rooms are heated to 21. A TRV in the bedroom will stop heating that room when it gets to 18 and a TRV in the lounge will stop heating that room when it gets to 21.

Eventually when the thermostat gets to 22 the heating turns off. If the TRV's are preventing that then the heating never goes off and it'll just keep pumping around warm water. The gas won't burn though as the return temperature if the water is high. When the return water temperature falls then the boiler will burn some more gas to heat it up again. Yes the heating runs "forever" but it's not burning gas in the process. When you go to bed you would turn the thermostat down to 18 degrees and the bedrooms will still heat to 18 but the living room would only get to 18 instead of 21 before the thermostat shuts off the heating completely.

phil24_7

Maybe a wireless thermostat would fit the bill?

It could be kept in the childs bedroom overnight and wherever during the day. TRV's on all radiators would still keep rooms below a certain temperature (once you get them set up right) as they would shut off once the room is hot enough.

It may take a couple of weeks to get the whole system set up just right (using small adjustments) but once it is you can forget about it...for the most part!

I_have_spoken

TRVs and properly balance the CH should do it.

If you want to get fancy, smart valves allows the user to precisely control the temperature in a room and introduces automatic running set periods during the day to tailor heating requirements.

Smiley_Dan

No, TRVs do not work. They control the radiator, not the boiler, so they won't be able to turn the boiler on and off. Furthermore they measure the temperature at the radiator, not the habited area of the room (which is why you don't normally see TRVs with temperatures on them).

A soft zoned heating system does this, such as Heat Genius or Honeywell Evohome.

SplanK

Smiley_Dan wrote: »

A soft zoned heating system does this, such as Heat Genius or Honeywell Evohome.

Although I agree that's the best way to do it, these options fall way outside the scope of being cheap/inexpensive....

It should be as inexpensive as possible, because we are pretty short of money by buying that house...

On the flip side, there was a requirement request for calling for heat from individual rooms.... these 2 requirements don't really go together that well! The more complex, the more cost.


The Evohome setup, you are talking >£500!!


Dual zone setup may be an option but I don't know enough about what systems are available. That usually requires the upstairs and downstairs rads put on their own separate circuits however....


TVR's are a good, cheap option and although will not call for heat they do a good enough job, just takes a bit of fine tuning.


The other option has already been mentioned of wireless thermostat of moving it, but I don't see that fixing your problem to be fair.


If you have problems heating up the bedrooms, then maybe you just need to maintain it? When was the last time the system was serviced? Could it be that the rads are gunked up? I have been going around mine as I have been decorating and flushing them through and it has made a difference to some rads.


Are there drafts in the room? Could you increase thermal efficiently by filling in gaps, making sure windows are properly sealed, heavy curtains fitted and a decent amount of loft insulation? Are the radiators large enough for the room? I have a room in our house which is to the north so gets very little sun and is noticeably cooler, it would probably benefit from a slightly larger rad to help.


Another option could be to cheap initial outlay maybe electric oil rads, but could be costly to run long term and is a bodge fix.

Smiley_Dan

Agreed about the cost, didn't read the OP well enough.

andre_xs

Thanks to you all for the interesting and helpful answers.

I've never realized the idea to use the TRVs in combination with a central thermostat. I have a question regarding this for the experts: You would basically set the TRVs to the desired temperature and the thermostat to a temperature so high that it is never reached (because the TRVs turn the radiator off before this). But this would probably incur additional costs in two ways:

- The pump (not the heater/gas, I'm aware of this) is running constantly, all the time - correct? I had a look at typical pumps and their energy consumption. This isn't too bad after all, but they often have a range specified (e.g. 7-48 Watt). If all TRVs are shut down because they have reached the temperature, would the pump then turn down to 7 W or try "full power" at 48W?

- Warm water is circulated all the time, even if all TRVs have shut down (however, then, the hot water would just circulate through the pipes, not the radiators). Once this circulating water drops below a certain temperature, the boiler turns itself on again. On the one hand, this sounds also like a waste of energy, but on the other hand the heat loss from the pipes just heats up the house, so that presumably the TRVs will go on a little later and thus, the heating periods are a bit shorter.

I'm trying to get a rough idea how much additional costs per year this strategy might involve. Maybe a more expensive wireless system pays off already after 2-3 years or so, then we may look into cheap ones...

An additional question regarding using the TRVs:
I don't know the exact plumbing in our house, but I presume that this requires that the radiators either are individually connected to the boiler, or that they have a parallel pipe running to them?

Smiley_Dan

Yes, that is not the ideal way of doing it, because your boiler continues to short cycle. Are you on gas? Not so bad there *if* it modulates well... Is it a condensing boiler?

The pump is not the issue with electrical consumption, it's the boiler firing. Mine uses 100-200W.

With regards the pump, normally you choose the power you want it to run at depending on your system. 7W is very low!

Water will not just "circulate through the pipes" unless you have dedicated bypass circuits. Most people don't, so they rely on a towel rail or one rad being on all the time.

southcoastrgi

Set the room stat to 21, fit trv's on all the rads apart from the one where the room stat is, if you have a fixed speed pump it will use just as much power when it's running whatever your heating is doing you would need a "smart" pump like a alpha 2 to have variable power usage, if all the rad valves are closed the water won't be pumping anywhere