How many radiators off a 22mm flow

[b21playa]

Hi all

I currently have 6 old radiators (downstairs) off what looks like 15mm pipework. It comes off the zone valve in 22mm and then goes under the suspended floor and is 15mm throughout. It takes forever to heat the rooms and as the radiators need replacing anyway I was looking to upgrade to 22mm pipework and then tee off in 15mm for each radiator.

The question is how many radiators can a 22mm pipe supply, I know as a rule of thumb 15mm shouldn't be anymore than 3. I have the following I need to fit for now on one side of the ground floor and as we refurbish other areas there will be another 5 rads which will come off a tee after the zone valve:

• 2 of 1400x600 K21
• 2 of 1600x600 K21
• 1 of 1200x600 K21
• 1 of 1600x600 K22

Is this doable?

Thanks in advance

 

[SJB060685]

What’s the combined output of these radiators? 22mm can supply up to 24kw

 

[b21playa]

What’s the combined output of these radiators? 22mm can supply up to 24kw

Hi

Looking at specs from manufacturer the 6 rads totals 12.5Kw or 43000 btu plus an additional 8kw or 27500 btu for the 2nd leg of 6 rads.

The upstairs will be off a separate zone valve which will total an additional 18kw for an additional 9 rads

So this should be fine?

 

[SJB060685]

Yes 22mm flow and return on that circuit should be fine, quite close but should be within limit providing your calculations are correct. Tap into the flow and return with 15mm for each radiator. You can get about 11kw through 15mm so could get a couple rads off one feed but that’s up to you. I assume the main boiler flow and return is at least 28mm?

 

[b21playa]

Yes 22mm flow and return on that circuit should be fine, quite close but should be within limit providing your calculations are correct. Tap into the flow and return with 15mm for each radiator. You can get about 11kw through 15mm so could get a couple rads off one feed but that’s up to you. I assume the main boiler flow and return is at least 28mm?

Thank you

Boiler is a Vaillant ecotec 438 with 22mm primaries. This will eventually be changed as I want to move from open vented to a pressurised system. Depending on tank/boiler I'm would have thought this would be 22mm as well, but leaving that for later.

 

[SJB060685]

22mm primaries are not big enough mate. Primaries need to be at least 28mm for the load they’re serving.

 

[b21playa]

22mm primaries are not big enough mate. Primaries need to be at least 28mm for the load they’re serving.

How far do the 28mm primaries need to go? Guess I'll need to upgrade my zone valves from 22 to 28mm

 

[SJB060685]

The 28mm primaries need to able to carry full load until you branch off for each zone and that zone has pipe work sized for its full load. To be honest it comes as no surprise you’re experiencing the problems you are with the current system.

 

[b21playa]

The 28mm primaries need to able to carry full load until you branch off for each zone and that zone has pipe work sized for its full load. To be honest it comes as no surprise you’re experiencing the problems you are with the current system.

It's the reason I want to change it all. Thinking about 28mm from boiler to 2 CH zone valves and a 22mm zone valve for DHW. Run this from the zone valve to upstairs in 28mm and then split in 22mm each direction, same for downstairs.

I can get the new rads on and do all that in 22mm and then when I get the boiler/tank done I will get the engineer to pipe 28mm to join my 22mm

 

[gpbeck]

Oversize rads and pipes to allow for future heat sources, with higher flows at lower temps.

 

[SJB060685]

Oversize rads and pipes to allow for future heat sources, with higher flows at lower temps.

Whereas I would normally agree with you have a look at his loads above. He’s around 38KW. Unless massive insulation upgrades are made I wouldn’t even consider a heat pump just yet.

 

[b21playa]

Oversize rads and pipes to allow for future heat sources, with higher flows at lower temps.

Rads are oversized for rooms

 

[b21playa]

Whereas I would normally agree with you have a look at his loads above. He’s around 38KW. Unless massive insulation upgrades are made I wouldn’t even consider a heat pump just yet.

Heat pump? I’m lost sorry

Currently the pipework under the floor has a hessian type insulation, this is being replaced with 20mm walled insulation

 

[SJB060685]

Heat pump? I’m lost sorry

Currently the pipework under the floor has a hessian type insulation, this is being replaced with 20mm walled insulation

That was a response to someone else’s comment about sizing radiators for low temperature systems. A heat pump is a low temperature system but that doesn’t mean a gas boiler can’t be either. My point was with your loads at around 38KW a heat pump is not a viable option and you could size the radiators for low temperature on gas boilers but these radiators would be much, much bigger. Finding a reference room to size the radiators in your case would be tricky.
I would ignore that comment and this as it was a response to someone else’s proposed option.

 

[b21playa]

That was a response to someone else’s comment about sizing radiators for low temperature systems. A heat pump is a low temperature system but that doesn’t mean a gas boiler can’t be either. My point was with your loads at around 38KW a heat pump is not a viable option and you could size the radiators for low temperature on gas boilers but these radiators would be much, much bigger. Finding a reference room to size the radiators in your case would be tricky.
I would ignore that comment and this as it was a response to someone else’s proposed option.

Thank you

 

[ShaunCorbs]

22mm will be on the boarder of doing it around 1.1ms

 

[SJB060685]

22mm will be on the boarder of doing it around 1.1ms

And increase to 28mm will reduce velocity but increase materials cost. You have to way up the pros and cons. I would not be overly concerned with a velocity of 1.1, it’s nowhere near max recommended and to be honest no system is 100% perfect

 

[b21playa]

I'll go with the 22mm for now and see how I get on, can always upgrade later when the boiler is being changed

 

[b21playa]

Just a quick update on the thread. Managed to remove old and install new rads this weekend. All pipes insulated with Bylaw stuff and what a difference it has made