15MM central heating pipes

[Barter78]

Hi All,

In need of some urgent assistance…

I'm getting a Worcester Bosch 30kw combi boiler fitted, the ground floor will be having two vertical rads (1800x472 double) in the dinning room and one in the front room, the boiler feeds water to them first as well as two pipes that go upstairs to my first floor where there will be one vertical radiator (1800x472 double) in bedroom one and horizontal radiator (600x1400 double) in bedroom two and a towel radiator in the main bathroom. The pipes then go downstairs to my hallway where there is a horizontal radiator (600x1400 double) and pipes also go up to my loft where there is a a horizontal radiator (600x1200 double) and a vertical radiator (1600x472 double) and a towel radiator in the en-suite….

All radiators are designer oval shaped….

BUT….

My central heating pipes through out the house are 15MM, only from the boiler about 4 foot do they begin as 22mm then it’s all 15MM pipes…

Will I need to upgrade the pipes as some that have given me quotes stated it could be an issue when balancing the rads and it’s best to upgrade the pipes….

please could you advise me accordingly - your advice would be much appreciated…

thank you….

 

[blup]

I have the same, flow always helps balance, is it a problem now?

 

[dilalio]

It's about resistance and the pump's ability to ensure flow rate suitable for all rads on the system.

22mm carcassing with 15mm loop offs is always much better.

 

[Barter78]

So, do I get the 22mm pipes installed or keep the 15mm - it’s a big job with a lot of pulling things apart?

 

[Barter78]

I have the same, flow always helps balance, is it a problem now?

It’s not a problem at the moment but when new rads go in it might be…..

 

[Madrab]

Can I suggest that you look very carefully at what radiators you will be installing and how they were sized? Are the rooms relatively small? I can just about guarantee that column rads are not a direct replacement for standard type 11/21/22 radiators if comparing outputs, when it comes to heating a similar space.

They also require a higher flow given their overall height hence the concerns of some of your installers re pipe sizes. A 22mm backbone to the upstairs hall with subsequent 15mm branches to the rads would probably be preferable.

 

[dilalio]

A 22mm backbone to the upstairs hall with subsequent 15mm branches to the rads would probably be preferable

And it's more likely to be suitable for low temp heating when we're forced down that route.

 

[Barter78]

Can I suggest that you look very carefully at what radiators you will be installing and how they were sized? Are the rooms relatively small? I can just about guarantee that column rads are not a direct replacement for standard type 11/21/22 radiators if comparing outputs, when it comes to heating a similar space.

They also require a higher flow given their overall height hence the concerns of some of your installers re pipe sizes. A 22mm backbone to the upstairs hall with subsequent 15mm branches to the rads would probably be preferable.

Hi,

Yes they are not big rooms, medium size rooms, the Btu is more then adequate for the rooms if not slightly overboard…

But will I be able to get away with having a 30kw Worcester Bosch boiler with 7 designer column rads (4 vertical and 3 horizontal all double) with my 15MM pipe setup across 3 floors?

Or is there something else I can do…

 

[Madrab]

the Btu is more then adequate for the rooms

You can use standard BTU calculators for column rads but don't expect the room to heat up the same way and as quickly as they did when convecting rads were used - if they were there previously

To explain - there are some basic assumptions when it comes to how radiators heat a given space - one of them is that convecting radiators are used to heat the air in the space and therefore gives a benchmark as to how quickly the rooms heats up and becomes warm to the occupant. Column radiators work in a different way and are not as efficient as heating the space, when it comes to anything but the smallest of rooms, unless there are oversized or several where there was one convecting rad previously. The reason for that is that they emit a large portion of their heat through radiation and not convection. Convection heats the air in a space far faster than passive radiation - heat emitted from a non convecting wet CH rad - as against IR/halogen/reflective radiation - which is different.

As far as using 15mm from the obligatory 1m from the CH boiler location out to the whole system then it can cause issues when it comes to feeding larger rads that are a distance away from the pump and usually requires very precise balancing. That may also need maintained over a systems lifetime as it ages, hence the recommendation to extend the 22mm to a more centralised location.

 

[Barter78]

You can use standard BTU calculators for column rads but don't expect the room to heat up the same way and as quickly as they did when convecting rads were used - if they were there previously

To explain - there are some basic assumptions when it comes to how radiators heat a given space - one of them is that convecting radiators are used to heat the air in the space and therefore gives a benchmark as to how quickly the rooms heats up and becomes warm to the occupant. Column radiators work in a different way and are not as efficient as heating the space, when it comes to anything but the smallest of rooms, unless there are oversized or several where there was one convecting rad previously. The reason for that is that they emit a large portion of their heat through radiation and not convection. Convection heats the air in a space far faster than passive radiation - heat emitted from a non convecting wet CH rad - as against IR/halogen/reflective radiation - which is different.

As far as using 15mm from the obligatory 1m from the CH boiler location out to the whole system then it can cause issues when it comes to feeding larger rads that are a distance away from the pump and usually requires very precise balancing. That may also need maintained over a systems lifetime as it ages, hence the recommendation to extend the 22mm to a more centralised location.

So, I don’t need to upgrade the whole setup to 22mm pipes just to a centralised location - could you very kindly elaborate on that please….

As I’m very reluctant to pull floor boards up and possibly cut into my ceiling as one trades man was suggesting….

 

[ericmark]

If and that's a big if, the lock shield valves are set correctly, it will not matter what size pipe is used. In a small home having the pipes size slowly reducing can assist in ensuring flow to all radiators whatever has been done with the lock shield valves. But as the home gets larger, we get to the situation where not all rooms are heated at the same time, so we have programmable TRV's and flow rate is changing all the time as TRV's gradually open and close, and the setting of the lock shield to stop the hysteresis is more important.

It was my late mothers house where I realised how important the setting of the lock shield valve is, she had a large radiator in her living room which also had a large bay window that would catch the morning sun. If the radiator is allowed full flow it will heat up fully before the TRV has time to close, once stinking hot it will continue to heat the room even when the TRV has closed, so speed at which it heats the radiator needs to be slowed down so the TRV can have time to regulate the temperature.

Since electronic TRV heads were used, easy, I had a target and current, and when no sun hitting the room, current should never exceed target, if it does close the lock shield a tad. And very soon each room was at the temperature required at the time required with no problem, well a slight problem, the anti-hysteresis software in the TRV's was OTT, so 7 am set to 22ºC and 8 am set to 20ºC to speed up morning reheat.

When the house was sold all the electronic heads were swapped for simple mechanical clearly lost the when rooms were heated, but the temperature worked A1 now all lock shields set, and radiators may get hot, but in the main just warm enough to maintain the room at set temperature and the boiler modulated as it was designed to do.

There was a wall thermostat in the hall, but that just stopped the boiler running in the summer, it was set slightly higher than the hall TRV, so winter all rooms TRV controlled.

However this system relies on the room with the wall thermostat being normally kept cool, on ground floor, and no alternative heating and also will cool faster than any other room in the house. This house it does not work, two reasons, one not a modulating boiler, and two the hall cools too slowly. One can adjust heat up rate, but not cool down rate.

As to radiator position, @Madrab makes a good point, the standard idea is we get a natural circulation, and the position of the TRV is well placed to have a reasonable good mixture of return air that it is sensing, however a hall with stairs is unlikely to get this circulation so the TRV does not really work too well, and place two radiators in a room 90º from each other and it is anyone's guess as to how the air circulates.

One can add to that windows, clearly double glazed are not the same as single, and there is two schools of thought, one allow air to be cooler and static around the windows, and two put heat right by the windows so the difference in temperature at the window is greater so you get more losses, not sure where that idea came from, but often radiators are under windows, but I think more to do with being where furniture will not stop the flow?

These pictures from central heating books do make one wonder what was in the minds of the writers, in the main draft was caused by open flue fires drawing their combustion air across the room from under the door, and was the reason for high backed chairs, the main gain with central heating was combustion air drawn from outside.

To maintain a room temperature is easy, the TRV does that, what is harder is to re-heat a room once it has been allowed to get cool, we want over size radiators to re-heat fast, so it means to maintain they are only warm. Dinning room is easy, we know when we are likely to eat, craft room, office not so easy, as often time of use not planned. My 12 mm micro bore will maintain the three story house great, but to re-heat cold rooms it is rather poor, so much depends what the rooms are used for.

One has to think about what you want, there is no right and wrong, if I want to reheat fast then fan assisted radiators are the way to go, if all rooms 24/7 kept at same temperature with no windows catching the sun, then under floor heating may work, but I love my windows catching the sun, so would never work for me.

So think about your home and what your life style is, and what re-heat times you want. Most of the calculators are for heat loss, not reheat times, and I have to say if I want to not allow rooms to cool, then 12 mm micro bore has no problem, it is only when looking at reheat times when one needs larger pipes.

 

[Madrab]

it will not matter what size pipe is used

Normally I wouldn't disagree but I have to here - Given experience and seeing a significant number of installers and DIY'ers in my time, keeping a system backbone of 15mm over 3 floors on anything more than 3 or 4 normal sized convecting rads would be a recipe for a really unpredictable system that would need really fine tuning and continuous monitoring/adjustment - fine if you are happy to do that, most clients I find aren't. Standard specs of the carrying capacity of 15mm pipe are - 10Kw @ 12deg drop @ 1.5m/s. That gives very little room for manoeuvre when it comes to 4 larger double verticals (~2kw ea), 3 larger standards (T22 = 2.5kw ea) and 2 towel rads plus the pipework, a 15mm F&R will struggle @ standard settings.

So, I don’t need to upgrade the whole setup to 22mm pipes just to a centralised location - could you very kindly elaborate on that please

Given the system you describe whereby it is set over 3 floors - then I would run 22mm up from the boiler into the upstairs hall then branch 15mm from that 22mm to each rad on that floor and up into the loft. Ceilings shouldn't be a consideration unless it's impossible to get down into the under floor space upstairs.

Downstairs can branch from the 22mm from below the boiler as it is just now (if I read it correctly) out to each rad, try and keep each rad on it's own branch to maximise heat up times and minimise balancing problems.

 

[Barter78]

Normally I wouldn't disagree but I have to here - Given experience and seeing a significant number of installers and DIY'ers in my time, keeping a system backbone of 15mm over 3 floors on anything more than 3 or 4 normal sized convecting rads would be a recipe for a really unpredictable system that would need really fine tuning and continuous monitoring/adjustment - fine if you are happy to do that, most clients I find aren't. Standard specs of the carrying capacity of 15mm pipe are - 10Kw @ 12deg drop @ 1.5m/s. That gives very little room for manoeuvre when it comes to 4 larger double verticals (~2kw ea), 3 larger standards (T22 = 2.5kw ea) and 2 towel rads plus the pipework, a 15mm F&R will struggle @ standard settings.


Given the system you describe whereby it is set over 3 floors - then I would run 22mm up from the boiler into the upstairs hall then branch 15mm from that 22mm to each rad on that floor and up into the loft. Ceilings shouldn't be a consideration unless it's impossible to get down into the under floor space upstairs.

Downstairs can branch from the 22mm from below the boiler as it is just now (if I read it correctly) out to each rad, try and keep each rad on it's own branch to maximise heat up times and minimise balancing problems.

Right… I’m with you now

 

[Barter78]

So, if part of the set is 22mm that should do the trick right?

 

[Madrab]

As it's sometimes referred to - the main backbone of the CH - the main feed and return should ideally be in 22mm and then the branches off to the rads are made in 15mm.