At 4.5 Litres per hour that's about 9 Lbs/Hr (0.9Kg/Litre)
At 19300 BTU/Lb that's 173700 BTU
173700 BTU = 51 Kw (divide by 3412)
Assuming normal boiler efficiency of, say 85% - then 43.3Kw output
That's a bit high unless you live in a small Hotel.
My gas boiler is 23Kw and drives a hot water tank and 16 radiators in a 10 room house.
Peccavi
June 2009