Heating circuit upgrade

[giacomo_z]

Hi,

I am looking for some guidance on CW pipework.

 

I have ~20-year old detached 2-floor house (91 sqm) with a heating loop in 22mm copper under the floor, which branches off to each radiator in 10mm microbore. I think the layout of the loop is per diagram below, although I have yet to take up any flooring to confirm. Boiler and DHW cylinder have been moved to the loft, roughly above the bathroom/bed2, near the gable. I indicated where heating pipes come down from the loft with red/blue squares (in the cupboard in the family bathroom).

 

I would like to upgrade this system to 22/15mm copper. Reasons for this are:

• I have a new Viessmann 200-W system boiler with a very high modulation ratio. It is running hotter than necessary because of the limited flow in the small pipes
• The floor joists are 7 x 2. From my calculation the maximum notch depth is 175mm / 8 = 21.88mm. Builders have clearly pretended this is close enough to 22mm. In practice, pipes are noisy when heating comes on and I think this is because there's little to no space for any felt.
• I have seen evidence of some pipe corrosion, which I think is due to old flux left on the pipes. Several neighbours have had pinholes in the past as well. I am keen to inspect the pipework under the floor and while at it I might as well improve it. 

 

Given the above, my preference would be to run most of it in 15mm, changing from a loop + branches to a radial system, with no more than 3 rads per branch (TBD based on max BTU per branch).

 

Questions:

• First of all, is my plan sensible?
• I would favour a layout which would allow me to do this in stages rather than all at once, so that I can tackle 1/2 rooms at a time, especially upstairs. Do you have any suggestion for the pipe layout?
• What is the max BTU I could put on a branch for a low temperature system? I assume this would depend on the maximum flow temperature because lower temperature means bigger radiators. These are old anyway so I wouldn't mind upgrading, if I found that was the new bottleneck. This would also be good for a future upgrade to ASHP.

 

I would like to also move to UFH downstairs, in the kitchen and dining/living (I could live with a radiator in the hallway and cloakroom), although this work would be done later. The plan is to:

• First upgrade the pipes
• Then tackle a bathroom renovation and install the UFH manifold. I am thinking to place this to the left of the bathroom radiator, in the stud wall (green box). Bathroom radiator will also be changed to a towel rail and moved to the cupboard wall (in magenta).
  • Is this a good location for a manifold? I would like to have it downstairs but I am struggling to find a good location for it.
• Finally move to UFH downstairs.

[marshian]

I'm struggling with the comment that the 10mm pipework is limiting flow to the rads and as a result you need to run the boiler hotter...........

 

I run drayton EB4 TRV bodies and the vast majority of the rads are using flow setting 1 out of 6 and that's a flow restrictor of less than 2mm diameter...

 

 

 

 

[giacomo_z]

Apologies, I omitted that I am running the boiler in weather compensation mode without a thermostat. The boiler modulates the flow temperature based on return temperature and outside temperature. Because of this, the boiler is "always on". The larger the pipes, the lower the flow temperature can be while still delivering the required heat to the room. So far I have never exceeded 50C this winter (first winter with this boiler) but I think I could do better with larger pipes.

[JohnMo]

Sorry I am 60 and not American, so don't use imperial units (BTU) and prefer to use kW.

 

So let's step back a little, a gas boiler at low flow temps is in operation mode pretty similar to a heat pump. So when you get down to low temps, the dT across the flow and return is about 7 to 8 degrees.

 

Your ring main is more likely to be the limiting factor not the 10mm tail.

 

At dT 7 10mm pipe can carry 1.61kW

22mm does 8kW.

 

Have read here

 

https://www.heatgeek.com/does-my-pipework-need-upgrading-for-a-heat-pump-with-cheat-sheet/

 

You need to understand the heating requirements of each room, and the radiator duty.  From there do the flow required through part of the system to get best pipe size for the flow required.

[OwenF]

Not sure how much this helps, but I had a similar decision to make - garage conversion combined with kitchen renovation. Over half the downstairs is going back to block so thought how to improve heating and water supply

whilst I’m at it.

 

Really fancied UFH in new kitchen but moved away mainly due to cost and somewhat due to complexity.

v200 boiler with variable mixing valves was looking to be eye watering £, plus cost of overlay system onto suspended floor.

 

New plan currently in motion involves:

- new V100 in loft above old garage (for lower modulation than current boiler)

- DHW cylinder relocated to loft next to new boiler (gains space from airing cupboard, give back to bathroom)

- cold, DHW & hot return manifolds in loft next to cylinder. Pipe from manifolds to each room in either 16mm & 12mm MLCP

- 2no. UFH manifolds in old airing cupboard (upstairs) & under stairs cupboards used as radiator manifolds. Location of each puts them central for all rads upstairs/ downstairs. Flow & return from boiler will run approx 10m from boiler to manifolds.

 

 

The main benefit (I hope!) of my strategy is that the majority of work I can do whilst the kitchen/garage is upheaved. However the manifolds mean I can commission just what gets done, then add to the system at a later date when I get to other rooms (if necessary chucking spare pipe under the floor for later)

 

Design has mostly been ‘by inspection’. I’ve done whole house heatloss and gradually upgrading radiators for dt25-ish MWT to room. Each radial leg from radiator manifolds will be in 16mm MLCP. Given the manifolds will be centrally located each leg will be similar length. Im hoping this means balancing at the manifold will be easy-peasy…

 

joke of it all is that the new v100, cylinder move and manifolds x5 cost probably as much as just doing UFH. I’m justifying I have a better whole-house upgrade for similar cost.

[giacomo_z]

@JohnMo: an Italian told off by (presumed) British for using British Thermal Units - hilarious 🤣 Joking aside, many thanks for link, I’ll have a read.

Assuming your guess is correct, 10mm is still not my favourite in terms of how it looks but I could just put a decent sleeve on it and reroute so that it disappears neatly into the wall.

It still leaves the problem of a 22mm pipe in a notch which is really too small for it though. If keeping the loop, how about replacing the 22mm with two 15mm next to each other where it crosses joists? In practice I would replace all the runs along west and east elevations.

 

@OwenF Many thanks for sharing. I already have a 200-W and a new cylinder so I would like to make the best of it now. I ruled out UFH upstairs because the joists are not hung to blocks but rather built into them and not sealed so I figured a good amount of it would be lost.
 

Manifolds are an interesting route which I considered but I dislike plastic pipes, although I get that I would be using the same thing for UFH but at least is downstairs.

Edited January 16 by giacomo_z

[marshian]

18 hours ago, giacomo_z said:

Apologies, I omitted that I am running the boiler in weather compensation mode without a thermostat. The boiler modulates the flow temperature based on return temperature and outside temperature. Because of this, the boiler is "always on". The larger the pipes, the lower the flow temperature can be while still delivering the required heat to the room. So far I have never exceeded 50C this winter (first winter with this boiler) but I think I could do better with larger pipes.

 

I'm not running weather comp but I am running flow temps between 45 and 50 deg C depending on the temp outside

 

I'm doing this thro EB bodies mainly set on 1..........

 

I really don't think you will get any benefit from increasing pipe size JM2pW