Btu/h factor for tankless coil

ThermalJake

Hi Guys, it has been awhile.

Sizong a hydronics boiler for 100,000 btu/h. How much higher do I go for the boiler with a coil?

Thanks as always.

Jake

Al Letellier

hot water demand from tankless

It depends on the capacity of the coil, but generally speaking we allow 15% of boiler capacity for the coil. If you have a 100,000 BTU heating load, a 115,000 net boiler should do the trick.

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ThermalJake

Thanks, Al (NM)

Michal_2

sizing boiler

look at the manufacturers data on the heater, they will post their minumum boiler btu/h. you can vary the size of the boiler with the gph of recovery you are looking for, naturally the higher the recovery the higher the input to boiler. Example a amtrol indirect wh-7 model with a 90 degree temperature domestic water rise will need 40,000 btu/h from the boiler, while at 70 degrees temperature rise it will make 69 gallons. Just make sure you match the circulator head and gpm for that indirect, as a engineer i see just what ever pumps put on these tanks and you lose the efficiency and recovery

DrV

load increase for boiler with coil

If your city water has lots of lime, the coil's heat transfer efficiency will drop. To mask this problem our oil company routinely installed 1.5 gph nozzels in residential burners rated @ 1 gph. They killed efficiency and they sold lots of oil extra oil. But, when we no longer had hot shower water, they would de-lime the coil, but leave the 1.5 gph nozzel. When we installed a GFX Power Booster, the problem vanished because we halved the shower load to under 10 kW (34,130 BTUH) even in the dead of winter. So, after the oil burner guy installed the 1.5 gpg nozzel, I changed it back to one rated @ 1 gph. This became an annual ritual until I got rid of the oil system.