The system currently in place has a Mexico boiler which is fairly old, but from what I understand that unless it becomes uneconomical to repair it's not cost (or environmentally) effective to replace it.
However, the radiators are extremely dated with many valves having either leaked or are leaking. It's also a single pipe system and the pipe work is not buried.
Therefore, is it a good idea to simply replace the radiators and pipe work and leave the boiler until it packs up for good. If it is, does the fact that it's a single pipe system make it more complicated/ impossible to replace it with a flow and return system.
The boiler is currently in the kitchen which is soon to be changed to a dining room/study if that makes any difference, such as if a new boiler would have to be sighted in a different room/position.
If a knowledgeable responder could also give a single-sentence definition of a single-pipe system I'd appreciate it (I mean, I can guess, but would rather not).
I think your idea idea crazy, valves leak so fix or replace them, I often can fix them. Go price your used radiators people sell. You might have better than are sold now, mine are heavy cast iron by a quality manufacturer about 90 yrs old and worth a good buck, better made than new radiators now. Single pipe, one in one side, one out the other, well thats fine as it always has been. Spend the money on a new boiler and insulation and save on gas.
The valves are relatively easily replaced. The pipework not so easily. You don't have to replacing the pipework: single-pipe systems do work (though they have disadvantages compared to twin-pipe).
If you're thinking Bigger Picture then not only would I consider replacing the pipework, radiators and boiler but also going for underfloor heating where possible and perhaps ground- or air- source heat pumps or a wood-burner. I don't mean getting all religious about any of these technologies: I mean /considering/ them, on their pros and cons.
The diagram shows the inlet at the top of the radiators. This is neither necessary nor the norm IME - usually both pipes are connected to the bottom of the radiators. My suspicion is that the diagram has been modifed from a gravity feed diagram. I have seen it done in rows of conceiled radiators, but that was so the on/off valve could be accessed at the top of the casing.
Whilst radiators on a single pipe circuit will sometimes have a valve for manual on/off, they don't have a valve for balancing flow.
The flow balancing is done using a single gate valve for each circuit. An installation would typically have 3 or more circuits, and these are balanced against each other, not by balancing individual radiators.
The comment about radiators at the end being colder is misleading. Yes they are colder, but that's taken into account in the system design. If you need equal power output from the radiators, they start off smaller and get larger further along the run. If they're all in one room, another way to do this is to space the initial ones further apart and the final ones closer together. A more common approach was to use unequal heat loss along a room to counteract it, so in a long office area, there might be more heat loss at the end-wall end than in the middle of the building, so the initial radiators were placed at the end-wall end.
Calculating radiator sizes with single pipe systems had to be done much more accurately than is now normally done, but in those days systems were designed by real heating engineers, so that was the norm anyway. It's probably going to be hard today to find heating installers who actually understand how such systems were designed, hence the derision by those who mostly don't understand them. It's not sensible to install such a system today, but comments about inefficiency (such as in that article) are mainly borne out of ignorance.
Doing what is said above ...small rads to start with getting larger and spacing them as described is unlikely to be practical in a domestic situation tho' is it ?
If you mean todays installers wouldn't have a clue how to work out the size or spacing, then I would agree, but changes in heating system designs have made that unnecessary, bringing down the skill level and costs involved in installation - an engineer isn't any longer required. However, the engineers who designed single pipe systems 50 years ago did exactly that.
Domestic situations don't tend to have 100' long rooms to heat with radiators running down the sides. You have one or two radiators in each room, and the power requirements to the rooms are likely to be different so you need different sized radiators anyway. Therefore it may not be obvious that the ones at the start of the circuit were sized relatively smaller than the ones at the end, verses what would have been done for a two pipe design, but that is exactly what was done.
Probably the most significant issue in converting a single pipe system to a condensing boiler is that the radiators won't have been oversized at all for the original system. In later installs, particularly with TRV's, radiators were usually oversized rather than actually perform the calcs to work out how big they needed to be, and this becomes a real advantage with a condensing boiler.
You are right about the pipes being connected at the bottom -at least on our system.
I have also read that its very hard to get rid of air locks in single pipe systems and if that is correct I'm wary about draining down the system to change a load of valves and then spending ages trying to remove air locks. Although having said that it's obviously easier then replacing the pipes and radiators!
The reason I'm thinking off changing the pipework is that the property is in the process of being redecorated and therefore it would be an ideal time to renew them and the radiators. Out of interest the pipework in the house is mainly stainless steel which I have discovered is a lot harder to cut than copper.
The house is about 45 years old and I assume the pipework and rads must be the originals and perhaps they will need replacing soon anyway. It's is just that I dont want to replace a boiler that while old is working perfectly.
My school had a single-pipe system pretty much exactly like the diagram. Big cast iron rads and 2 inch steel pipes. Solid and boy-proof.
Given when I went there and it being a part-Tudor building it could easily have been installed 50 years ago, when as you say they had proper engineers.
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