Should I replace PEX with copper?

[leemkule]

I have an old building that I'm gradually updating with the view to eventually having an ASHP or running my gas boiler at low flow temps.

 

It's a 4 bed house and at some point someone has ran JG speedfit to supply the master bedroom (22mm main run and 15mm to rads), en suite and second bedroom radiators. The rest of the house is copper.

 

I have been following heat geeks and urban plumber and the general consensus seems to be that PEX is a bad idea because the internal diameter is narrower and the fittings increase resistance to flow for a higher flow heating system like an ASHP.

 

Ideally I would like to eventually have an 'open loop' system with rads upstairs and UFH downstairs all running at 35 degree flow temperature after we gradually upgrade insulation/radiators/windows etc.

 

My question is, which is causing an argument in my house, should I upgrade the PEX to copper? My rather uneducated view is that if copper is superior for low temp heating flow rates I should upgrade the pipework to copper while the walls / floors are accessible and not plastered, my partner thinks it's a waste of time given that I don't fully understand the effect it will have on flow rates and also that we may never get end up getting an ASHP.

 

What are peoples thoughts? Thanks! 

 

 

[JohnMo]

22 minutes ago, leemkule said:

should I upgrade the PEX to copper

You need to do the maths - it's that simple. Nothing wrong with any pipe material, if it supports enough flow for the required kW heat required.

 

Steps

1. Understand your room heating requirements. You need to know this anyway if you are going to run low flow temperature as your radiators need to be sized.

2. Determine pipe size needed. This will be different in different parts of the house as the system branches out. So at heat source if the whole house needs 6kW, the first pipes from heat source need to carry 6kW at you flow temperature and dT. Then as it branched to upstairs and downstairs each branch needs to carry approx 3kW. If you had 3 rooms on upstairs and 3 downstairs then each room would need 1kW in very simplistic terms. So the parts of the system need to be selected based on your actual heat loss figures.

 

Sorry no black and white answer - how long is your piece of string?

 

Heat geek has a cheat  sheet for pipes and kW and dT.

 

It may not be an issue if it is look at last paragraph below.

22 minutes ago, leemkule said:

all running at 35 degree flow temperature

You would really run weather compensation, so you trickle heat into house. So I assume max design temp of 35 degs (so coldest day flow temperature)?

 

Most of our heating system is Hep2O piping, so doesn't need to be an issue. There are ways around a higher than ideal pressure drop, just insert a fixed flow rate pump on the return leg back to heat source. Then tune flow rate to get the rates you need. As long as it's run fixed speed no issues arise with a variable speed elsewhere in the system.

Edited Saturday at 14:21 by JohnMo

[leemkule]

27 minutes ago, JohnMo said:

You need to do the maths - it's that simple. Nothing wrong with any pipe material, if it supports enough flow for the required kW heat required.

 

Steps

1. Understand your room heating requirements. You need to know this anyway if you are going to run low flow temperature as your radiators need to be sized.

2. Determine pipe size needed. This will be different in different parts of the house as the system branches out. So at heat source if the whole house needs 6kW, the first pipes from heat source need to carry 6kW at you flow temperature and dT. Then as it branched to upstairs and downstairs each branch needs to carry approx 3kW. If you had 3 rooms on upstairs and 3 downstairs then each room would need 1kW in very simplistic terms. So the parts of the system need to be selected based on your actual heat loss figures.

 

Sorry no black and white answer - how long is your piece of string?

 

Heat geek has a cheat  sheet for pipes and kW and dT.

 

It may not be an issue if it is look at last paragraph below.

You would really run weather compensation, so you trickle heat into house. So I assume max design temp of 35 degs (so coldest day flow temperature)?

 

Most of our heating system is Hep2O piping, so doesn't need to be an issue. There are ways around a higher than ideal pressure drop, just insert a fixed flow rate pump on the return leg back to heat source. Then tune flow rate to get the rates you need. As long as it's run fixed speed no issues arise with a variable speed elsewhere in the system.

Hi,

 

Thanks for the comprehensive reply. 

 

1. I have done the heat loss calculations for my house. The rooms on that 22mm branch (15mm down to rads) of hep2o in total require have a combined heat loss of 1456 watts and I have oversized my radiators appropriately for running a 35 degree flow temperature.

2. This is part that confuses me. If this branch only needs 1456watts, is my 22/15mm enough? I've seen the heat geeks pipe size chart which is helpful but it goes on to say 'First of all, these numbers are NOT for plastic pipes.  The plastic pipe should absolutely NOT be used in a heating system, and particularly not on a heat pump, in our opinion, for many reasons which we will do a video on soon.' So how do I know if my pex is suffice and how come heat geeks are saying plastic should definitely not be used on a heat pump? They didn't go on to make that video as to why plastic is in their opinion not appropriate; however my only inference from their other videos is that the connectors and pipe inserts increase resistance. What's your thought on all this?

 

That's interesting that your house is mostly piped using hep2o and that there's ways around if there is a too high of a pressure drop.

 

Edited Saturday at 14:46 by leemkule

[JohnMo]

Do a search on Google and look for a Hep2O technical manual. It will give you pressure/head loss rates for different rates and temperature per 100m.

 

We have a 6kW heat pump it wants to flow around 18L/min doing heating and 20L/min doing DHW.

 

We are all UFH in house so the run from ASHP to UFH manifold is in 28mm Hep2O, it supports more than 6kW, it's a long run, approx 15m each way. We also tee off to a summer house for a fan coil this is approx 15m again but in 15mm Hep2O, zero issues. So far everything is driven from a ASHP circulation pump. We have an issue with cylinder heating as the existing run (previous gas boiler) pipes change to 22mm and another 10m run. We couldn't get the required flow through the system so I just added a pump for that leg which starts when the diverter valve moves for DHW heating.

[marshian]

2 hours ago, leemkule said:

Hi,

 

Thanks for the comprehensive reply. 

 

1. I have done the heat loss calculations for my house. The rooms on that 22mm branch (15mm down to rads) of hep2o in total require have a combined heat loss of 1456 watts and I have oversized my radiators appropriately for running a 35 degree flow temperature.

2. This is part that confuses me. If this branch only needs 1456watts, is my 22/15mm enough? I've seen the heat geeks pipe size chart which is helpful but it goes on to say 'First of all, these numbers are NOT for plastic pipes. 

 

Can you tell me the size and type of rad for a room or rooms because it's easy to work out what flow you need and as a result of the flow rates needed check the pipe sizes will cope.

 

example a T22 600 high by 1400 wide running a flow temp of 35 deg C, a return of 28 deg C at a differential pressure of 30kPa would output 375 W when supplied with a flow rate of 46 litres/hour

[leemkule]

53 minutes ago, marshian said:

 

Can you tell me the size and type of rad for a room or rooms because it's easy to work out what flow you need and as a result of the flow rates needed check the pipe sizes will cope.

 

example a T22 600 high by 1400 wide running a flow temp of 35 deg C, a return of 28 deg C at a differential pressure of 30kPa would output 375 W when supplied with a flow rate of 46 litres/hour

 

Thanks for the reply.

 

So both rooms have column radiators (bought before I knew of T22, T33 etc as I thought bigger rad = better) the biggest radiator on that branch of the system is 966mm x 600 mm (6 column, 21 section). Delta 50 output 1974 Watts, so I calculate at delta 15 (flow temp 35, room temp 20) it would output 415 w. How would I work out the differential pressure and output for this rad?

I could give you the details of the others too if that helps.

[marshian]

41 minutes ago, leemkule said:

 

Thanks for the reply.

 

So both rooms have column radiators (bought before I knew of T22, T33 etc as I thought bigger rad = better) the biggest radiator on that branch of the system is 966mm x 600 mm (6 column, 21 section). Delta 50 output 1974 Watts, so I calculate at delta 15 (flow temp 35, room temp 20) it would output 415 w. How would I work out the differential pressure and output for this rad?

I could give you the details of the others too if that helps.

 

966 width, 600 high? whats the depth?

 

To get closest to 1974 W from a T22 at T50 it would need to be either

 

400 high by 1800 wide (1969 W)

500 high by 1600 wide (2092 W)

700 high by 1200 wide (2029 W)

 

So that seems like a really high output for the size of the rad but I'm not familiar with column rads??

 

Differential Pressure is linked to pump head - for my rads I have a 1.8m pump head so I use 18kPa as my differential pressure for all my rad flow calcs and it seems accurate enough

 

 

[leemkule]

10 minutes ago, marshian said:

 

966 width, 600 high? whats the depth?

 

To get closest to 1974 W from a T22 at T50 it would need to be either

 

400 high by 1800 wide (1969 W)

500 high by 1600 wide (2092 W)

700 high by 1200 wide (2029 W)

 

So that seems like a really high output for the size of the rad but I'm not familiar with column rads??

 

Differential Pressure is linked to pump head - for my rads I have a 1.8m pump head so I use 18kPa as my differential pressure for all my rad flow calcs and it seems accurate enough

 

 

 

It's a 6 section deep column radiator which is why it's so high output, the depth is 230mm, height 500mm (600 with feet) and 966 width:

 

https://www.homesupply.co.uk/Apollo-Roma-6-Column-Steel-Column-Radiator-With-Feet-600-x-996mm-WF6C5H1000

 

It has 21 sections, according to the spec sheets its 1.87 litres per section, so holds 39.27 litres of water apparently

[marshian]

13 minutes ago, leemkule said:

 

It's a 6 section deep column radiator which is why it's so high output, the depth is 230mm, height 500mm (600 with feet) and 966 width:

 

https://www.homesupply.co.uk/Apollo-Roma-6-Column-Steel-Column-Radiator-With-Feet-600-x-996mm-WF6C5H1000

 

It has 21 sections, according to the spec sheets its 1.87 litres per section, so holds 39.27 litres of water apparently

Hmm that's a chunky thing........... any boiler or ASHP is going to love your system volume

 

Their on line guide says at 15 deg difference between room temp and flow temp is 0.206 x T50 output so that's 412 W

 

The Danfoss calculator I use says for a 500 x 100 x 250 column rad it's 273 W with a flow rate of 34 litres per hour but clearly they have a base line for column rads that has a lower water capacity/surface area

[leemkule]

5 minutes ago, marshian said:

Hmm that's a chunky thing........... any boiler or ASHP is going to love your system volume

 

Their on line guide says at 15 deg difference between room temp and flow temp is 0.206 x T50 output so that's 412 W

 

The Danfoss calculator I use says for a 500 x 100 x 250 column rad it's 273 W with a flow rate of 34 litres per hour but clearly they have a base line for column rads that has a lower water capacity/surface area

so I know how to work out the output but how do I work out the flow required for this rad and therefore see if my pipe diameter is adequate? I dont wanna go to the effort and cost of replacing the speedfit with copper if I dont need to

[marshian]

10 minutes ago, leemkule said:

so I know how to work out the output but how do I work out the flow required for this rad and therefore see if my pipe diameter is adequate? I dont wanna go to the effort and cost of replacing the speedfit with copper if I dont need to

 

JG 22mm speedfit is 30mm OD and 22mm ID according to a quick google?

 

Max Flow rate thro a 22mm ID pipe at 0.3 bar (ie 3m Head) is around 14 litres a min or 840 litre per hour

 

OK you are going to have some restriction at the 15mm drop down but it doesn't seem to me like you need to convert to copper on the face of it

 

I would but all my house is copper and I've never used plastic

[leemkule]

18 minutes ago, marshian said:

 

JG 22mm speedfit is 30mm OD and 22mm ID according to a quick google?

 

Max Flow rate thro a 22mm ID pipe at 0.3 bar (ie 3m Head) is around 14 litres a min or 840 litre per hour

 

OK you are going to have some restriction at the 15mm drop down but it doesn't seem to me like you need to convert to copper on the face of it

 

I would but all my house is copper and I've never used plastic

 

I think those figures are off. 22mm speedfit is the external diameter with an internal diameter more like 18mm and the 15mm has an internal diameter of approximately 12mm.

 

 

[JohnMo]

52 minutes ago, leemkule said:

 

I think those figures are off. 22mm speedfit is the external diameter with an internal diameter more like 18mm and the 15mm has an internal diameter of approximately 12mm.

 

 

Yes the same as Hep2O.

[marshian]

21 hours ago, leemkule said:

 

I think those figures are off. 22mm speedfit is the external diameter with an internal diameter more like 18mm and the 15mm has an internal diameter of approximately 12mm.

 

 

 

OK re-running the calcs for 18mm ID 20 metre length it's down to 7 litres a min or 420 Litre per hour

 

Just for info or context my largest rad is 700 x 1400 and it's a triple panel triple convector at a 35 deg flow temp it needs 94 litres per hour to meet the heat loss of the room 640 W (22mm copper two pipe circuit with 15mm tails to the rad)

 

For me I still don't think you will have a problem with flow rate thro that circuit