underfloor heating and buffer tank

wex13

Looking for some experienced answers. Renting a 1700 sq ft bungalow built about 8 years ago with poor insulation - 4" in the attic so Im guessing the walls have minmum in the cavity. UFH with 250 litre buffer tank. Carpets in half the house. Owner left instructions that best settings was for buffer tank was top thermostat at 60 and bottom at 30 and set stats at 16 in rooms and 20 in bathrooms and leave the system running. Basically I'm surprised at how much oil I've gone through in a month - approx 1/3 of a tank.
The system is set up so that the boiler can be called on 24/7 by the tank and the UFH pump is on a switch. For the past month I would swith on the pump before leaving the house and switch it off when home in the evening so running for 12 hours a day. House is nearly too warm.
What is the most economic / optimum way of running a sysstem like this?
1. Leave at as it is?
2. Place a time clock on the pump for say 3 hours in the morning and 3 in the evening and leave the tank call the boiler 24/7?
3. Place a time clock on the pump and boiler for say 3 hours in the morning and 3 in the evening?
Any advice would be appreciated as I've never come across UFH or buffer tanks before.

Condenser

wex13 wrote: »

Looking for some experienced answers. Renting a 1700 sq ft bungalow built about 8 years ago with poor insulation - 4" in the attic so Im guessing the walls have minmum in the cavity. UFH with 250 litre buffer tank. Carpets in half the house. Owner left instructions that best settings was for buffer tank was top thermostat at 60 and bottom at 30 and set stats at 16 in rooms and 20 in bathrooms and leave the system running. Basically I'm surprised at how much oil I've gone through in a month - approx 1/3 of a tank.
The system is set up so that the boiler can be called on 24/7 by the tank and the UFH pump is on a switch. For the past month I would swith on the pump before leaving the house and switch it off when home in the evening so running for 12 hours a day. House is nearly too warm.
What is the most economic / optimum way of running a sysstem like this?
1. Leave at as it is?
2. Place a time clock on the pump for say 3 hours in the morning and 3 in the evening and leave the tank call the boiler 24/7?
3. Place a time clock on the pump and boiler for say 3 hours in the morning and 3 in the evening?
Any advice would be appreciated as I've never come across UFH or buffer tanks before.

The house should be set to what ever temp you find most comfortable when you're in and allowed to drop away by 3 degrees or so when you're not in or in bed. Imo the rooms and toilets should be set to the same temp because the colder room only "robs" heat from the warm one.
You should also note that UFH is much harder on oil than a rad system because you can't really let it fall away too far in temp as it has a slower response time. Thats why its best if UFH is run with a heat pump and rads with oil boilers. You're probably not going to improve your situation as the house has poor insulation and, as I mentioned, ufh is harder on oil. I'd say 1/3rd of a tank is about right for the situation you are in.

The Parrot

also the tank seems to be very small as a buffer tank. surly a well insulated 500 + tank would work far better. and cause the boiler to cycle alot less.

wex13

Has anyone monitored something like this before?

jp99

wex13 - I have UFH with oil in a new build along with 500lt buffer tank. Although I have solar (60tubes) and stove linked to buffer tank as well I don't need to rely on oil as much. I would only use the oil for an hour a day when needed to bring the tank from 20deg to 55deg ish and light the stove then to keep the temp in buffer tank topped up for UFH. Solar doing nothing for me at this time of the year although up to August was helping contribute to buffer. Before I moved in I had to dry the screed on both both floors before any tiling happened leaving the oil on 24/7. Emptied 500lt of oil in 2 weeks so it really easy to see it go when using oil 12 hours a way in your case.

Do you have stats in every room? You could switch off some stats in rooms you don't use to save hot water in your tank. I don't know if a back boiler stove is an option for you to retrofit in although its my main heat source I'm finding out to run UFH at this time of the year. If you keep running 12 hours a day your going to need around 4 fills of oil a year which is crazy.

F.D

jp99 wrote: »

wex13 - I have UFH with oil in a new build along with 500lt buffer tank. Although I have solar (60tubes) and stove linked to buffer tank as well I don't need to rely on oil as much. I would only use the oil for an hour a day when needed to bring the tank from 20deg to 55deg ish and light the stove then to keep the temp in buffer tank topped up for UFH. Solar doing nothing for me at this time of the year although up to August was helping contribute to buffer. Before I moved in I had to dry the screed on both both floors before any tiling happened leaving the oil on 24/7. Emptied 500lt of oil in 2 weeks so it really easy to see it go when using oil 12 hours a way in your case.

Do you have stats in every room? You could switch off some stats in rooms you don't use to save hot water in your tank. I don't know if a back boiler stove is an option for you to retrofit in although its my main heat source I'm finding out to run UFH at this time of the year. If you keep running 12 hours a day your going to need around 4 fills of oil a year which is crazy.

Hi Jp99 do you ever over heat the tank by having the stove on, eg no stats calling for heat? we just have a regular cylinder heated by the boiler coming on and off, but its using a lot of oil by doing this, just wondering if i could put in a stove and larger cylinder would it be a simple way to reduce our oil consumption ?

jp99

F.D wrote: »

Hi Jp99 do you ever over heat the tank by having the stove on, eg no stats calling for heat? we just have a regular cylinder heated by the boiler coming on and off, but its using a lot of oil by doing this, just wondering if i could put in a stove and larger cylinder would it be a simple way to reduce our oil consumption ?

Hi F.D, occasionally I would turn off the stats just to take power showers when only the stove is on to build the temp in the tank up. It would never overheat as there is a stat for the stove which can be adjusted if needed. We have a heated towel rail also which will be used as a heat dump if it was to overheat. I'm not sure if your cylinder is undersized, my buffer feeds underfloor water loop of 2600 sq ft house. What size space are you heating

F.D

Heating approx 2000 sqft, the living and dining area is a vaulted celing and open plan so i have a stove in there so in theory the under floor is only heating the bedrooms and hall, i have no rads or towel rails but is using a lot of oil for just half the house you could say, so thats what has me thinking if i changed the stove to one with a back boiler and put in a bigger cylinder it could be cheaper/easier than putting in the like of an out door wood boiler
You mention your stove has a stat ? what type is it. ideally the system would heat the buffer during the evening when we have the stove on and the under floor could pull out of that until its lit again the following evening

jp99

F.D wrote: »

You mention your stove has a stat ? what type is it. ideally the system would heat the buffer during the evening when we have the stove on and the under floor could pull out of that until its lit again the following evening

The stat is on the stove pipe input to the buffer tank. When commissioning the heating system and firing up the stove for the first time there was a massive banging noise on the pipes (water was too hot I'm guessing) so had to knock the stat down to 60 and its been left there since with no reccurence.

This is very much the same as how we work it as out of the house all day until the evenings except for weekends. Looking forward now to getting some summer sunshine and see how the solar helps with everything setup.