Piping and pickup factor

S Ebels

When the rest of you hydronicians size a new boiler (hot water) what if anything do you allow for the P&P factor? Do you allow anything at all. I used to but then gradually noticed that all these systems seemed to be borderline oversized. I now go strictly by the DOE or AFUE output numbers. I haven't had any problems and I sure think that they would have showed up this past Jan./Feb. Quite a few days at design or less.

I realize that if a person encounters an old gravity system with 3" mains and standing cast iron you have to allow for the P&P but what about todays systems? A lot of times we are using Pex which loses far less heat than copper or steel in the first place.

What say Ye?

Paul Pollets

allowances

I allow 10% for pickup factor, and try and stay close to the connected load. Always asking if the owner plans to remodel or add more heated space. If there's an indirect tank installed, I size for the recovery of the tank to be within 10-15 min for a 53gal. I like to see 80-100K BTU's available to recover the indirect. In the Seattle climate, it's common to see heat losses in a 3500SF new home under 40K Btu's. Putting in a 50K BTU boiler may heat the space, but would be too small for additional load. Of course, having a modulating boiler makes it all easier.

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eric legacy

losses



D.O.E. is only what is available at the outlet of the boiler.

Net IBR has a factored in 15% de-rate for combined piping and pick-up losses which are based on fin tube radiation in an unheated basement on a 1 or 2 zone split monoflo loop. (Lots of losses) That is too much in new tight construction multi zone homes. 5% is more reasonable.


Remember IBR is an oganization comprised of members from various boiler and radiation companies e.g. wiel mclain slant fin ect. They came up with the formula long ago. With fuel prices the way they are going there should be a more exact de-rate other than 15% across the board.

On the other hand for a converted steam system with some original large piping 20 to 25% factor should be used to cover losses from large pipes and to get the system up to temp quickly,but I would offer to insulate the piping instead.

e.l.