delta t - the delta t number installers in Navan argue about.
Two bids can look similar while assuming different delta t values; the cheaper one often specs down. Ask for the figure in writing and check it against the manufacturer datasheet before you sign.
Dillonsland, Johnstown and Aerodrome: Local housing mix shapes emergency plumbing specs here. Year-round emergency plumbing demand in Navan. Updated for plumbernavan searchers.