Oil boiler buffer tank with underfloor heating

[Rushworth]

I have been following the posts on UFH from an oil boiler to buffer tank or not with keen interest as for one reason or another I am looking to install an 35 KW oil combination boiler to provide A, DHW on demand and B, for the existing UFH system. I have talked to a number of plumbers and have had similar experiences
To other posters in that I have found it difficult to get a concise answer on the best route to go with the set up so I want to do as much homework as possible so that I can get my own head round the thing and be much better placed then to find a good installer. I am not looking to install anything solar just yet but would be useful to bolt on later. I would welcome any advice and experiences.

Rushworth

 

[dcawkwell]

No need for a buffer tank.
An oil boiler of any sort will drive underfloor.

You will need to zone the underfloor and radiator circuits if any.

My personal advice would be to use normal radiators rather than underfloor. I replaced an oil boiler in a barn conversion recently.
Switched on radiators and upstairs where nice and hot in no time.
Downstairs it was still freezing hours later. Underfloor heating
got there in the end.

 

[Rushworth]

The reason I was thinking along the lines of a buffer tank is that I know UFH systems operates at a much lower temperature than that required for radiators (which are not an option) and oil boilers are either on or off affairs and thought that a store of water for the UFH to draw from would reduce the cycling of the boiler so that when it is running it does so for a efficient length of time.
From what has been said it would appear that I could run the UFH direct from the boiler but the water would need to be obviously lower than that for DHW.
Would the UFH come off the primary or the secondary water circuit?
The weather compensation sounds interesting so looking into that, that said I can regulate the temperature in each room/zone manually using the distribution manifold, very low tech I know but works a treat.
A mate has mentioned a mixing valve to control the temperature of the warm water for the UFH; any advice would again be welcome. Come to think of it a rough drawing might be good so I can get my spinning head to stop! Cheers everyone.

 

[simond]

You have to be very careful taking the route of connecting ufh to a condensing oiler.

It is not advisable to turn the temp down to the max of the ufh, eg 45c. Most oil boilers will be damaged by corrosion forming in the primary steel heat exchanger. This is down to the construction of an oil condenser which is very different to a typical gas condenser.

The is usually no need for a buffer vessel, although you could use a device such as that made by Chelmer Heating if you wanted have something a bit better than average.

 

[dcawkwell]

The reason I was thinking along the lines of a buffer tank is that I know UFH systems operates at a much lower temperature than that required for radiators (which are not an option) and oil boilers are either on or off affairs and thought that a store of water for the UFH to draw from would reduce the cycling of the boiler so that when it is running it does so for a efficient length of time.
From what has been said it would appear that I could run the UFH direct from the boiler but the water would need to be obviously lower than that for DHW.
Would the UFH come off the primary or the secondary water circuit?
The weather compensation sounds interesting so looking into that, that said I can regulate the temperature in each room/zone manually using the distribution manifold, very low tech I know but works a treat.
A mate has mentioned a mixing valve to control the temperature of the warm water for the UFH; any advice would again be welcome. Come to think of it a rough drawing might be good so I can get my spinning head to stop! Cheers everyone.

The oil boiler will be set to 70 degrees. The central heating pipes will be at 70 degrees. The underfloor heating pump and blending valve keep the
underfloor to the desired temperature with the use of the blending
valve. If the underfloor is dragging heat out of the central heating pipes
rapidly then the oil boiler shouldn't cycle that much.

 

[Rushworth]

Oh dear, corrosion in the heat exchanger, which sounds like a very bad hair day and the buffer tank idea is bleeding to death.
So it comes down to is this, what is the best way to have the boiler connected to the UFH system so that the boiler is running at its optimum heat output and yet delivering warm water (20c to 35c) to the UFH.
I still like the idea of using a combination oil boiler with the hot water on demand (as shower is electric) If anyone has a similar setup I would really welcome there advice and experiences as to the best way forward.
Cheers all.

 

[Rushworth]

I take the point about the 70 degrees. What is a blending valve?
Cheers

 

[Agile]

A lot of those replying have not noted that he ALREADY has the UFH and no rads!

Much as I dont like them I do see a thermal store for DHW and UFH as a possibility.

Either the OP is surrounded by nupty plumbers or he plans a DIY install.

This is also a case where I see a heat pump as a very viable solution!

Tony

 

[simond]

If you want a simple ufh and a combi then the standard manilold mixers connected to the boiler enabling the return temp to be kept up above the danger zone would be perfect.

However you also suggest you may like to incorporate solar thermal at a later date.

In which case, ditch the combi idea, and fit a buffer store/thermal store such as the Chelmer Heating unit, and you have the best of both worlds. albeit at a cost.

When you dig deeper, being green is usually very expensive in heating solutions. you might want to visit ecoBUiLD next week at Excel, there will be loads of people wanting to talk to you there.

 

[Rushworth]

OK, there are some very useful suggestions. As I mentioned I might at some stage look at solar panels so going with a non-combi would open the way for that.
With regard to plumbers I have spoken to three and got three totally different answers that all added up to the same thing, installing an air to water system (which I am all to familiar with) and that is not on the table. All three lost interest when I did not fall for the sales pitch on replacement ATW.
I can show the electricity bills to prove it but more to the point bills for parts! Live expectancy of ATW seven years, two parts two years ago £3073.89, last year another inverter £867.48
So I am trying to gather as much info as possible so that I can purchase the right boiler and most definitely do not intend to do a DIY install. I have one very recommended plumber who I intend to use when I have got my head round this part but he is quite literally on the other side of the planet at the moment and arrives back (hopefully the right way up) in August.
I know nothing about oil boilers but I know pretty much everything there is to know about scroll compressors, inverters, the four companies’ in the world who mix refrigerant gases, there combinations and heat coefficients. I have not ruled out alternative ways to heat a home and boil a kettle!
Cheers all.

 

[Norcon]

Have a look at Grant oil boilers. Are usually well recommended.
They also supply a weather compensator kit which is ideal for ufh and looks after boiler return temperatures.

Have a word with dedicated ufh installers who will be more up to speed and savvy with control systems.

 

[Norcon]

If it is a CONDENSING COMBI the flow temp can be set below the max temp for the UFH and a blending valve is not needed.

From Grants MI's...
Combi V3, Combi Max and Vortex Combi models

3 Boiler thermostat - This control allows
adjustment of the temperature of the water leaving
the boiler to heat either the radiators or the hot
water, via the hot water heat exchanger.
The boiler thermostat has an operating range of
75°C to 85°C. For optimum hot water operation,
ensure this is set to maximum

Also...

On underfloor systems it is essential that the return is
pre-heated by mixing flow water into the return before
it enters the boiler. To prevent internal corrosion of the
boiler water jacket, the return water temperature must
be maintained above 55°C for the Combi V3 and
Combi Max and 40°C for the Vortex Combi

You might need to have a re-think there mm.

 

[Rushworth]

I am looking at the Firebird enviromax heat-pac C26 condensing oil boiler with a Reliance UFH control setup for temperature control from boiler and return to boiler. The Grant vortex was suggested and that looks good also. I am also looking at weather compensation but not to sure about the real benefits of that just yet. If any one has any comments about the Firebird range I would be interested.
Cheers all.