UFH design principles

[mistake_not]

Hi,

 

Hoping for some design help / thoughts for a planned UFH installation. I have done some searching/ reading on previous posts but still have questions.

 

The context: I am renovating an extending our house, and looking to install UFH downstairs. We are going to dig up the existing floor slab and lay insulation/ screed so we are not dumping heat into the ground (as well as one other insulating changes). Upstairs will remain as rads, but may convert to UFH in the future, however a few rads will always remain.

 

I have been playing around with loopcad, and looks like I will have 3 or 4 loops of 60ish M.

 

The questions: should I aim for the same flow rates across the loops, same length, or something else? 

 

Also should I be looking for a specific manifold/ pump design for mixing rads and UFW? I previously had a single loop on my last house with a very small manifold. I just set the mixer to fully open and used a Tado thermostat with WC to turn it on an off which worked ok, but not great as the PiD control couldn't be set manually so would overshoot.

 

Edit: I am planning single zone and all actuators open: so assume I want the same flow rate on all?

 

Thanks for any help / advice.

 

Toby

Edited December 31, 2023 by mistake_not

[ProDave]

Let me be the first to say don't mix UFH and radiators.  they have such different heating characteristics.  If you really must then do it as an S plan with a 3 channel programmer so you can have different upstairs and downstairs heating times.

 

You don't say the heat source, but if an ASHP then DEFINITELY don't mic them.

 

Conventional system is an UFH manifold so you can set the flow rates for each loop and if you desire have individual room thermostats  That would be fed from the heat source via a 2 port valve.  another 2 port valve would feed upstairs radiators and the third 2 port valce is for the HW tank.

 

 

[mistake_not]

Thanks for the quick reply @ProDave.

 

Yes S plan and different channels and valves is the plan (and existing set up for HW / CH).

 

Questions were more about manual manifolds Vs electronic as well as WC electric mixers.  Also my assumption is it's best to have the UFW all running same flow rate.

 

Heat source is boiler but obviously wil likely change to ASHP in the future as boilers go away.... Can't afford to do entire house in one go, hence going to be mixed rads / UFH for a while.

[JohnMo]

Flow rate is set per loop length, there is no need to have the same or similar loop lengths. Salus self balancing a actuators will balance the system for you, on a fixed dT, just add one per loop.

 

I have used both mechanical and electronic mixers and prefer the electronic ones. By electronic I mean 3 way valve and actuator controlled to a set or varying temperature. The reason I like, is that they always provide a good recycle flow back to the boiler and only mix when required not all the time.

 

Is UFH right for you? Home all the time and happy with heating nearly all the time it's great. Away all day and heating off don't expect to warm before you go to bed.

 

UFH in bedrooms is rubbish, either not warm enough or too warm. Avoid.

 

Can you existing boiler do weather compensation? If so S and Y plan should be avoided, consider X plan or priory hot water.

 

Low temp radiators or fan coils, would be my vote doing it all again.

 

 

[mistake_not]

Thanks @JohnMo. The Salus actuators look good.

 

Any suggestions on electric mixer / 3 way valves? Have done some googling and haven't found much, the only examples I have found are this:

 

https://www.heatingcontrolsonline.co.uk/ectc-with-sensor.html

 

And this

 

https://www.tiasystem.co.uk/products/manifolds-and-cabinets/mixing-pump-sets/mixing-pump-unitwith-an-electric-actuator,produkt118/

 

However the simple answer is spec electric actuator/ mixer rather than thermostatic and let the plumber sort....

[JohnMo]

Not cheap but wireless

https://www.ebay.co.uk/itm/231266783709

 

 

[Roger440]

We fitted UFH to a house that was otherwise radiators with an oil boiler.

 

Ive found it to be very succesful. Better than i could have though.

 

I installed it up to and including the manifold which has a stat and pump on it. Then i got someone competent to connect it to my existing system.

 

The stat on the floor is set to 40c. 

 

The UFH is buried in the slab, 120mm thick from memory.

 

Its been discussed on here before, but digging up and relaying will likely cost a good chunk. Whilst you will have heatloss if you dont, that few £k will buy an awful lot of energy. Worth running the numbers and looking at payback. Id guess at decades, rathen than single digits in years. Especially with an overlay system, which gives you a (small) thermal break from the concrete flloor.

 

[NandM]

On 31/12/2023 at 17:34, JohnMo said:

Low temp radiators or fan coils, would be my vote doing it all again.

 

 

 

@JohnMo - do you mean you'd pick low temp rads over UFH?  Is that because of the times you're at home, or something else?

[JohnMo]

3 minutes ago, NandM said:

 

@JohnMo - do you mean you'd pick low temp rads over UFH?  Is that because of the times you're at home, or something else?

For the renovation yes, or extension. Doing UFH correctly on a renovation so you get really low temps isn't easy and if you do the rest of the system flows at a different temp, so it a fudge, your heat source efficiency doesn't gain.

 

Fan coils, set your flow temp at 35, your heating is sorted, set a heat pump at 12 to 15 and the cooling is sorted also.

 

UFH will always include an additional chunk of downwards heat loss, that you don't get with radiators or fan coils. Example I have a floor U value of 0.09, so pretty good and the floor sits at around 23 to 24 during the heating season, with a room temp of 20, my downward heat loss automatically increases by 15 to 20% because of it.