critique of house plumbing plan

[Coll659]

Hi again all

 

As i work through all the plans for my full renovation of the house im buying im now hoping to get some of your knowledgable feedback on my water plans. 

The house is an old house which will get a complete renovation and currently the house has nothing other than the mains mdpe coming in so I need to design and install and full system. Ive done a fair bit of basic plumbing but never on this scale and designing a full system so i have been trawling this forum to get tips and come up with a plan but im sure there are plenty of errors in this first draft. 

 

NOTE: Im sure all of my symbols that I made are not correct so apologies for that, hopefully they are close enough for you to see what I mean.

 

I have gone here for the manifold system after seeing all the advice on this form. For simplicity I have opted to go without a HRC. The runs to the kitchen sink will be approx 6-7 metres from manifold (manifold next to UVC). The runs to bathroom will be approx similar. Most of the pipes will run under insulation on concrete floor ( I insulate pipes and cut slots out of bottom of PIR boards to acomodate pipes) 

 

Im doing this house in Slovakia and for some reason I cant seem to find the UVC multiblock valves here (with the balenced feed and tee for expansion vessel) so I will just put in a balancing valve separately (Or would a PRV suitable instead?) followed by a tee off for expansion with a safety valve. 

 

I hope it makes sence and i thank you in advance for any tips or criticisms you have, im sure there are plenty

[JohnMo]

Heat system comments

 

8kW heat pump, so will a flow rate of about 1.5 to 2m³/h will be needed, 25mm pipe sounds too small? Have you done a pressure drop calculation, using the internal bore.

 

Why do you need the volumiser? You rarely need a volumiser on UFH as the floor (concrete or screed) will absorb heat very well. Especially if running open loop.

 

Why do you need the check valve on the return to the heat pump? Your expansion vessel and pressure relief should be there. So it's after both the heating and cylinder return.

[Coll659]

thanks for the reply

 

12 minutes ago, JohnMo said:

8kW heat pump, so will a flow rate of about 1.5 to 2m³/h will be needed, 25mm pipe sounds too small? Have you done a pressure drop calculation, using the internal bore.

I haven't done that, I didnt really think there would be a problem here so I clearly need to do some researching on this. The outlet from the heat pump is 25mm and all the gubins they are quoting me with the heatpump (anti freexe valves, 3 way valves etc.) are 25mm which is why i went with that

 

14 minutes ago, JohnMo said:

 

Why do you need the volumiser? You rarely need a volumiser on UFH as the floor (concrete or screed) will absorb heat very well. Especially if running open loop.

Yeah I know, the heat pump company are insistent on it for warranty reasons. I will at least use it as a volumiser and not buffer

 

15 minutes ago, JohnMo said:

Why do you need the check valve on the return to the heat pump? Your expansion vessel and pressure relief should be there. So it's after both the heating and cylinder return.

This was on the install drawing from the heat pump company so I just followed that. not necessary then? 

[Coll659]

 

23 hours ago, JohnMo said:

8kW heat pump, so will a flow rate of about 1.5 to 2m³/h will be needed, 25mm pipe sounds too small? Have you done a pressure drop calculation, using the internal bore.

So i checked some stuff on this. Sorry i'm on learning curve here so apologies if i am say something stupid. 

The specs all say DN25 which i discovered is the nominal diameter which is different. im guessing this would be standard 28mm pipe (or possibly 35?). The connections to the in line anti freeze valve etc are g1". But I will try and confirm pipe size with the company soon. would 28mm (or 35mm) sound a better size? 

 

Flow rates:

looking over my underfloor heating plans I added up the flow rate for each loop and came to a total of 10.2 l/m (i think this translates to 0.612m3/h). Does this sound right and do I need to add for DHW or anything else?

 

Pressure drop:

I did a pressure drop calculation using an online calculator based on a 28mm copper pipe (inside diameter 25.6mm), flow rate of 10.2 ltr/min, over a distance of 6m and a temperature of 40c and it gave me a result of 0.37096 Kpa or 0.00371 bar. My problem is i have not got far enough into my research to really know what this means or why its important but I will do some research. But does this sound ok? 

[Coll659]

After Johnmo's feedback ive been away and done a load more research and calculations and looks like if I use 28mm copper the velocity and pressure drop will be comfortably within limits. Thanks for that

 

Any feedback from anyone on anything else in the plan (positioning and types of valves etc). any problems you can see or things i'm missing or doing wrong? appreciate any feedback if you have it. 

 

Thanks again

Colin

 

 

[JohnMo]

On 12/05/2025 at 19:22, Coll659 said:

looking over my underfloor heating plans I added up the flow rate for each loop and came to a total of 10.2 l/m (i think this translates to 0.612m3/h). Does this sound right

Sorry missed you last response. Your heat pump will want to run at twice that rate. I just opened all the UFH flow meters fully and let the heat pump do what it wants. To balance the rooms you just trim the hottest room flow down a little. Your 28mm will be fine for this.

 

Make sure your expansion vessel for heating system is after the filter on the return.

[Coll659]

Yeah you are totally right. After doing all my calculations I found it was actually basically double this rate exactly like you said.

I've planned all my pipe spacing to hopefully make balancing pretty easy. 

 

And thanks for the note on the expansion vessel I'll make sure to do that.