New Plumbing, and Underfloor Heating System

[revelation]

Hi all,

 

We are starting work on our plumbing next week.  However, stumping on some information online and on youtube, I am now slightly concerned.

 

Our original plan was to use a system boiler, and a 250 litre tank, for our heating we were looking to have UFH in screed on the ground floor, and UFH between joists on the 1st floor and Loft.  We were going to have each room in the house zoned so that each room can have its own individual temperature (we have a few extremes of temperature preferences in our household). 

 

From what I have read and seen is the general recommendation is to run the system on all the time so its at room temperature, so a low temp from the boiler (with weather compensation) and let that run through the system without mixer valves etc (in theory is makes sense).  That way a consistent temperature is achieved the boiler is always condensing and its supposed to be the most efficient way.  

 

I have a very good and competent plumber, but his experience with actually setting up UFH systems through a whole house are very limited so whilst I know he will connect things properly if he has some instruction.   Could anyone provide any advice or pointers to resources that will give the ideal set up.    An efficient system that will still give us flexibility to control individual temperature.

 

Thanks in advance :)

 

 

[PeterW]

3 hours ago, revelation said:

From what I have read and seen is the general recommendation is to run the system on all the time so its at room temperature, so a low temp from the boiler (with weather compensation) and let that run through the system without mixer valves etc (in theory is makes sense).  That way a consistent temperature is achieved the boiler is always condensing and its supposed to be the most efficient way.  

That won’t work for a number of reasons. 
 

With UFH temperatures and a standard boiler - your boiler won’t get low enough. It “just about” works with an ASHP as they operate in the 35-45°C space but boilers don’t. You need a buffer tank of probably 100 litres to allow the boiler to not short cycle. 
 

Also, each zone will need its own actuator and controller, and you will also need pumps on each floor ideally. If you want different temperatures everywhere then I would look at a manifold per floor and ensure you get the pipe spacing properly calculated. 

[revelation]

I have been advised that the Viessmann 200 is suited to running UFH at low temp?

 

We have a manifold that will serve the ground floor (on the ground floor) and a manifold in the loft that serves the first floor and the loft.  We will have actuators and heat miser controls/stats in each room.

 

 

[PeterW]

So you will need 2 manifolds with all pumps and blenders. 
 

Veissman 200 19KW can modulate down at best to just shy of 2kW however that is at non condensing temperatures and still at a flow temperature of 50°C with a return of 30°C. The 50°C is too warm for a UFH supply and when you are at delta 7°C which is optimum for UFH flow and return you will be short cycling the boiler at its minimum setting when around 30-40% of the zones are satisfied. This will be exacerbated by having multiple manifolds potentially at different temperatures. 
 

Veissmann recommend (and size) the use of Low Loss Headers in this sort of situation - I’ve no idea on the heat load you require but a 60 litre LLH is probably the minimum I would specify and even then it would depend on the load / design of the remainder of the system. 
 

How many bathrooms / showers / occupants have you got in the house ..? 250 litres isn’t a big tank and you will struggle to recharge with a smaller system boiler. Go upward on the sizing of the boiler to keep the tank hot and the minimum power of the boiler burner will increase on the heating which will mean you need a larger buffer / LLH. 

[revelation]

We only have 4 occupants currently 2 adults and 2 young children.  We have two bathrooms (one with bath & shower, one shower only) and a cloakroom (toilet/wash basin),  its a 4 bed house

 

This is one of the videos I have seen that suggests the boiler can do this?