UFH - 4 floors, 5 manifolds, 500sqm area, HOW MANY FLOW/RETURNS?

[Internet Know How]

Hi All,

 

I have UFH to install on my new build property, and I wanted to ask how many separate flow and returns are required to each manifold from the boiler. I'd say each to have a dedicated flow/return back to the boiler room, however what are your thoughts to reducing this down to 3 x flow/returns to all 5 manifolds?

 

What are the drawbacks to this?

Is it even recommended as it would reduce the heat up time if 2 manifolds are sharing the same flow and return?

Will the UFH equipment provider agree/disagree?

 

Setup:

 

lower ground: 1 manifold (12 port)

ground floor: 2 monifolds (5 and 10 port)

First floor: 1 manifold (12 port)

Second floor: 1 manifold (10 port)

 

Thanks

 

C

 

[LA3222]

I wonder who will be the first to say you don't need UFH on anything other than the ground floor of a well insulated etc. build🤔

 

FWIW, I have three manifolds (2x13 ports and 1x2 iirc) and they feed off a single flow/return. I have it in 28mm up to where it branches off - each branch is 22mm to the manifold. I have a pump on that 28mm flow and then a pump each on the two big manifolds. Nothing on the 2 port...it relies on the push from the 28mm flow pipe pump. No issues with flow.

 

280m2 - yours will maybe need two flow and returns in 28mm? 

Edited May 10, 2023 by LA3222

[PeterW]

2 hours ago, Internet Know How said:

Setup:

 

lower ground: 1 manifold (12 port)

ground floor: 2 monifolds (5 and 10 port)

First floor: 1 manifold (12 port)

Second floor: 1 manifold (10 port)

designed by whom ..??

 

So at a broad calculation that you can get a maximum of 10m/sqm of floor space, you have the entire 500sqm with every piece at 100mm centres ..?? At a conservative 70W/sqm are you seriously saying your peak heat load is 35kW..??! 
 

Assuming this is correct (unlikely) then I would suggest you install a tandem pair of boilers and run a pair of zones - one for each alternate floor with basement and first paired, and ground and second paired. 28mm F/R with a decent pump would be fine but would still run a buffer on each circuit to reduce potential short cycle. 
 

Other alternative is to run a 6-700 litre thermal store and also include a preheat coil for DHW and just dump all heat into that - again, pair of boilers for redundancy.

 

I expect the layout is actually incorrect and going to 150mm centres would reduce down to an 8 port per floor which would be ample but I would still use twin boilers etc as per above. 

[Internet Know How]

Ok so here is the final design

 

4 floors, 5 manifolds. 1 floor has a 12 and 10 port manifold, and the others either a 10 or 12 port manifold. All pipes to have 150mm centres. Going for smart stats that apparently have a couple of years life in them. Maybe I should have gone with the hard wired stats like I did in the current house but anyhow, decided the smart with app control. 

 

We will have 2 boilers linked for the entire house

Edited June 30, 2023 by Internet Know How

[JohnMo]

Sorry for the rant but I am just amazed, but not in a good way.

 

This is plain daft. Why would you need two boilers on any new build even at 500m2.

 

Have you done any heat loss calculations, or are you just making it up as you go on? It must be a poor quality build, that didn't comply building minimum requirements to require 2 of the smallest boilers a available. And why would you want the control issues and poor efficiency you are likely to see.

 

Smart stats are just marketing bull, with UFH, you need a very low hysterisis thermostat. Why because UFH just reacts slowly the bigger the hysterisis the more the room temp fluctuates and less efficiency you get from the boiler. The ideal hysterisis is circa 0.1 degrees most smart thermostats will be 0.5 degs if you are lucky. Smart just means they connect to internet, which is not needed with UFH as reaction time is too long to make any use of switching the heating on when you are driving home.

 

FYI - My 193m2 of UFH (225m2 house) has a single manifold with 7 loops and one thermostat.

 

 

[Lofty718]

Agree with @JohnMo 2 boilers is daft, Run one boiler or heat pump and keep everything as open loop as possible.

 

If you genuinely want something 'smart' that will boost efficiency run your boiler on weather compensation. A single Vaillant ecotec plus 637 shold be sufficient for your property.

 

Vaillant boiler correctly sized

Sensocomfort vrc720f

VR71 wiring centre

ESBE mixing valves to control UFH instead of manifold mixer

 

Is what I would get.

Edited June 30, 2023 by Lofty718

[Kelvin]

That’s one big house with a complicated heating setup. It must be full of pumps too! As per above. One manifold and 8 loops and no heating at all upstairs. 

[Dave Jones]

stick to 100mm centres if you want to go for low flow temp for maximum efficiency. Dont/limit zoneing. Get it airtight and size doesnt really matter.

[JohnMo]

58 minutes ago, Dave Jones said:

stick to 100mm centres if you want to go for low flow temp

Only really true for a high heating demand, not true at all if the heat demand is below about 20W/m2 and the lower it gets the smaller the difference becomes. The difference between 100m and 300mm centres is 1 to 2 degrees mean flow temp.

 

The only real difference between 300 and 100mm centres is reaction time to a heating input. With 100mm being much quicker.

 

Most heat pumps for example will only output 25 degrees flow at the lowest setting.  With UFH due to the very slow reducing return temperature, controlling heat source can be an issue. At 25 degree flow mine for example would fire up and run for about 20 mins, then take a break, looking for a return drop below a set threshold, but lots of hours later the return never did, I had to up the flow temp to 26, then it all worked as it should.

 

Nothing is black and white.

[TonyT]

On 10/05/2023 at 20:50, Internet Know How said:

Hi All,

 

I have UFH to install on my new build property, and I wanted to ask how many separate flow and returns are required to each manifold from the boiler. I'd say each to have a dedicated flow/return back to the boiler room, however what are your thoughts to reducing this down to 3 x flow/returns to all 5 manifolds?

 

What are the drawbacks to this?

Is it even recommended as it would reduce the heat up time if 2 manifolds are sharing the same flow and return?

Will the UFH equipment provider agree/disagree?

 

Setup:

 

lower ground: 1 manifold (12 port)

ground floor: 2 monifolds (5 and 10 port)

First floor: 1 manifold (12 port)

Second floor: 1 manifold (10 port)

 

Thanks

 

C

 

 

is the property built yet?

what services do you have?

what type of construction do you have in the floors?

do you have a plant room, cupboards in each floor for accessible manifolds?

any PV?

 

[Dave Jones]

2 hours ago, JohnMo said:

Only really true for a high heating demand, not true at all if the heat demand is below about 20W/m2 and the lower it gets the smaller the difference becomes. The difference between 100m and 300mm centres is 1 to 2 degrees mean flow temp.

 

The only real difference between 300 and 100mm centres is reaction time to a heating input. With 100mm being much quicker.

 

Most heat pumps for example will only output 25 degrees flow at the lowest setting.  With UFH due to the very slow reducing return temperature, controlling heat source can be an issue. At 25 degree flow mine for example would fire up and run for about 20 mins, then take a break, looking for a return drop below a set threshold, but lots of hours later the return never did, I had to up the flow temp to 26, then it all worked as it should.

 

Nothing is black and white.

 

100 gives you more options though.