underfloor heating with condensing oil boiler

Hello everyone. just wondering how long you need to leave on to get desired temp of 20 degrees. do you leave boiler running 24/7 and leave stats do work because i think if you use set back modes on stats the boiler has to heat everything from cold. would installing a buffer tank make it more efficant? thanks

There are many many posts here on AAM dealing with that exact issue and yes a buffer tank installation is the best design available for UFH. It will, of course, depend also upon your particular installation as to whether which set up is best suited.

thanks shane. The boiler is located in garage with flow and return ran to hot press in house. I was thinking of putting buffer tank in garage beside boiler.If i do this the hot water storage in the house will have to be heated from the buffer tank also as is on seperate time clock to underfloor heating.The underfloor is controlled by heatmiser with each zone bring on boiler as called for. Do you think fitting a 500litre buffer will make it more efficant as client has burnt 800 euro of oil since 1st nov with underfloor on only 2 hours in morning and 2 hours in evening and in set back mode to 16 degrees all other times? thanks

Yes this is the best location for the buffer tank. Depending on the output of the boiler, it should take approx 35 mins for 35kw boiler to bring to ideal buffer tank temperature of 75C and approx 55 mins for a 26kw. This should give, for UFH, approx 2 - 2.5 hours of heating based on a ΔT of 30C.

The dhw does not have to be heated from the buffer. Just install pipework to bypass the buffer tank in conjunction with a motorized valve, either 2 port or 3 port and this will bring water directly from the boiler to the cylinder coil. Ideally you should have a motorized valve on the cylinder coil and at each manifold to eliminate stats opening actuactors when not wanted and to eliminate any open circuits getting heat when hw is called for.

I would consider putting a solar coil in the buffer in case solar panels are added in the future. Then in summer, the buffer can be heated by solar and the buffer can heat the dhw cylinder in the hot press. The solar can also contribute to heating the tank on sunny days in winter also.

With regard to €800 of oil since 1st Nov, I would look more closely at the controls. Heatmiser are excellent controls, however, they have to be used correctly. At a guess, I would say that there is no motorized valves anywhere on the system, therefore, dhw is being heated whilst UFH is and any open circuits are also getting heat. Minimal work would correct this.

For Heatmiser to heat hw, just change one of the thermostats to a Heatmiser PRTHW-N Room Stat. For convenience this will usually be located in the kitchen. It has a built-in function to call for hw through the UH1, therefore it will also open the necessary zone valves as required. Cable used for this should be CAT5e Screened.

Here's a similar design I done.

Oil_Solar_Buffer_Heating_System_Diagram1.pdf