One pipe system condensing boiler.

Would a one pipe system work efficiently on a condensing boiler as the return type would likely be below 54c all the time. So the boiler would run in condensing mode. Alot of condensing boilers don't run in condensing mode.

It’s designed for 80c so won’t condense

Yes but it would have a large Delta T with it being a one pipe system or is that wrong?

Matt0029 said:

Yes but it would have a large Delta T with it being a one pipe system or is that wrong?

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No as the rads would suffer / be cooler it would be the opposite be a smaller dt normally 10c or less

Thanks as in not all the water will go through the rads. Some will just flow around the system. Resulting in the shorter DT?

Matt0029 said:

Thanks as in not all the water will go through the rads. Some will just flow around the system. Resulting in the shorter DT?

Click to expand...

Correct and stops the rads having a massive td

Depending on why you are asking, these ideas might be relevant:

A modern condensing boiler will be significantly more 'efficient' than an elderly non-condensing boiler even when the former isn't running in 'condensing' mode. This is because the newer heat exchanger will be more efficient. However, If you are intending to fit a new boiler to an old one-pipe system you need to be really careful about cleanliness. One-pipe systems are difficult / impossible to flush clean with the radiators in situ and residual sludge will probably clog a modern heat exchange rather quickly. So, the choice is essentially (a) hydraulic separation, i.e. the the boiler connected to one side of a heat exchanger and the one-pipe system connected to the other, or (b) upgrade the radiator system to a two-pipe configuration and future proof by sizing for low-temperature emitters.

In a one-pipe heating system with a condensing boiler, the key to efficiency lies in keeping the returning water temperature low. Condensing boilers work best when the water coming back to the boiler is cool, ideally below 54°C (130°F). This allows the boiler to extract more heat from the exhaust gases, saving energy.

To make sure it works well, you need to ensure the boiler isn't too big for the space it heats. If it's too large, it might turn on and off too often, which isn't efficient. Also, how the system is set up matters — things like making sure the pipes are insulated and the radiators are the right size can help. Regular maintenance is also important. Keeping the boiler and system in good shape ensures it keeps working efficiently over time.