Boiler Usage

stevesuch

Hi, Can someone help me understand how our boilers and heating works?! This may sound obvious, but we've just had underfloor heating installed in an extension alongside the existing radiators to the rest of the house. We have an unvented cylinder and a traditional boiler.

Now if I've got the radiators on and that thermostat has triggered so the boilers running, if I also switch on the underfloor heating is there an increase in Kw/Hs or more draw from the boiler?
Or is the boiler just on or off?

The rads don't seem to take any longer to heat up, so is it more economical to just say, if you're turning one thing on, you may as well switch everything on?
Thanks!
 

Reed_Richards

Boilers can be quite sophisticated.  In the simplest case they will come on at high output and heat the water leaving the boiler to a certain temperature and keep going until the water returning to the boiler gets too hot then turn themselves off for a while.  If you add extra heating capacity like extra radiators or extra underfloor heating then it will take longer for the water returning to the boiler to get too hot so the boiler will be on longer for each cycle.  This will cause it to burn more fuel so increase the running cost.

A more sophisticated boiler will modulate down its output to try to prevent the returning water getting too hot, any reasonable modern gas boiler will do this, an oil boiler almost certainly will not.  Then on top of this there are even more sophistications where a boiler can vary the target water temperature according to how cold it is outside or how far away the actual room temperature is from the set temperature on the thermostat.

If you were just running one or two radiators then the return water would get hot very quickly and the cycles would be short.  Short cycling tends to reduce the efficiency of operation.

Underfloor heating tends to respond very slowly so you may find that you need to keep it on for long periods in order to keep it working satisfactorily.  Hopefully it has its on "zone" and so can be controlled and timed independently of the radiators.     

Exodi

Out of interest, wet underfloor heating or electric?

Wet can take a very long time to heat up - ours takes about 3 hours before you can even tell it's on (but then it keeps getting warmer/stays hot long after the heating is switched off. The key to wet UFH is being proactive).

tacpot12

You would be better off asking the underfloor installer how it works. There are a number of different ways it might be setup to work, and you need to have an accurate explaination if you are to be able to use it efficiently.

matelodave

As said above it depends how your system is configured but essentially if you turn on the underfloor heating as well as the radiators then your boiler needs to work harder or run longer to produce the extra energy required to heat a larger area.

Generally radiators run at a higher temperature than underfloor heating and often an underfloor heating system will have its own controls (programmer or room stat etc), possibly an extra pump and a mixing valve to reduce the water temperature to the floor.

Its also quite possible that the u/f system controls are interlocked with the boiler insofar as it can activate the boiler or control the floor temperature independently of the other room stats. Its something your installer should have instructed you about so you can run the system efficiently.

markin

Is the new room open plan?

Is the boiler a condensing model? With a water drain coming from it.

The new extension will be at a good insulation standard but it will still add more load if heated and not closed off.