Oil pipe size selection for supply from tank to boiler

[John Chapman]

OFTEC Technical Information Book 3 gives a chart for selecting the size of oil pipe from a top-outlet tank to a central heating boiler's oil pump. For my new tank this would give a 6mm diameter pipe (for a

25 metre run and a pump about 1 metre above the tank base). My problem is that my new tank has a bottom outlet, not a top outlet, and I'm wondering - based on an old posting here by [e-mail], if my memory serves me rightly - whether different logic applies as a consequence. My old tank used a 10mm pipe (gravity feed, not far from the boiler) and I intend to use that existing pipe as it is buried in the concrete floor of my utility room. To allow this re-use I'll incorporate a GOK (instead of Tigerloop) de-aerator as this new GOK device is OFTEC approved for use indoors (the Tigerloop is only for external installation and I don't want to have to run a second pipe through the concrete floor to my boiler!). 6mm pipe does seem to me rather small for a 25 metre run and the final portion to the boiler has to remain 10mm diameter. The logic behind OFSTED's chart is to balance flow resistance against the risk of air build-up in the pipeline. Has anyone got relevant experience, or advice, before I finally decide my plastic-clad pipe diameter?

John

[John]

All the theory is very nice but you will find that using 10mm pipe will be just fine. In fact as 10mm is almost universally used it is cheaper to buy in most cases than "odd" sizes. Why do you want to install a tiger loop or GOK device - are you precluded from raising your tank base to level or slightly above the burner? With the larger sized pipe your losses will be less and its unlikely that you will have any pump cavitation problems whatsoever. In fact one of the smaller boiler manufacturers do suggest that with a 1 metre lift its unneccessary to worry about this. I do however have personal severe reservations about using a one pipe system with more than this (unless you want to incur an ongoing problem of premature oil pump failure)

HTH

John