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Pipe sizing – a pitfall when upgrading your heating system

Many properties can be much improved by a heating system upgrade. Switching out radiators can improve style, function and convenience and really update the look of a room. Having a set of new radiators installed can be costly enough but not many people understand that it can also lead to disappointment and trouble.

I’m writing this post because I see these problems all too frequently and would love it if more customers could avoid them.

Pipe sizing is important when considering a radiator upgrade

Every boiler and heating system uses a whole lot of pipes to perform its functions but not all pipes are equal. It makes sense that small pipes can only serve small radiators and so on but this can be easily overlooked in practice.

8mm-10mm pipes can’t do everything

Typically if pipes are 8mm or 10mm, this can be a problem.

This is because small volume pipes end up carrying less water around your system but at a higher pressure.

Pipe pressur

Many homes have been installed using the small gauge pipes. They may have been just about good enough with the initial heating system. As time goes by radiators may be replaced without taking the pipe gauge properly into account. That can put increased stress on the boiler and start causing a range of problems.

Sometimes the home owner or landlord would like to upgrade the radiators but may not be aware of this issue at all. It would normally be up to the gas plumbers that come out to see the job to point out the problem with the overall pipe size. A good gas plumber will be able to properly assess your system pressure requirements and be realistic about what it will take to deliver the heating system upgrade you need even if that involves more work than you thought. Sometimes this means spending more on the job overall.

Adding new radiators too large for small gauge pipes may cause you some severe heating system problems.

  • Your boiler can get shut down because of too much internal temperature (not enough flow)
  • Your radiators can be poorly warmed at the extremes of your property
  • Radiator valves upstairs can be put under too much pressure and suffer undue wear
  • Your boiler can suffer increased wear and develop faults

The bottom line is, if you want a modern high performance heating system in a normal sized home or larger, it’s unlikely to be achieved on 8 or 10mm pipes.

What’s my advice if you have 8mm or 10mm pipes but want to upgrade?

If you’re faced with this problem my advice is to take a longer term view of your heating system ambitions. Find a plumber you can trust to help you get a decent idea of the heating system you want for the foreseeable future of your property. Whether you can fund the upgrade in one go or need to do it in stages, it means that you upgrade things in the right order and always to increase the health and performance of the system. Sometimes this means refitting pipes throughout part of the property.

I recommend at least 15mm gauge for most jobs and ensure new installs I do always use them where appropriate. I don’t mind sharing that I practise what I preach. In my own home the heating system that came with my house was using small gauge pipe. I’m very satisfied to say that I ripped it all out and installed a much more capable 22mm and 15mm pipe system and an ideal boiler. Now as I’m upgrading my radiators (I’m going for vertical ones) the system has more than enough capacity to cope happily with the new demands.

If you have already upgraded to oversized radiators and are having issues but don’t want to upgrade to larger pipes right now, often the best course of action is to replace larger radiators (especially on the ground floor), with smaller ones. This can ease the issue and return a system to health but it may take the radiators you want off the menu until the fundamental issue with pipe size is addressed.

If as a customer, you are overly price conscious you may have a tendency to encourage plumbers to try and work around the issue and give you just the radiators you want ignoring the risks to the health of the system. Sometimes the plumber that’s telling you what you don’t want to hear is the one being the most honest.

What I want to avoid is half measures that cause problems, damaging boilers and ultimately people ending up unhappy with their heating system upgrade. I’ve seen all kinds of inappropriate work done for all kinds of reasons and am always distressed when a customer has misspent money on a heating system upgrade.

I hope this has been useful, if you’d like some more specific advice, please don’t hesitate to contact me.

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