stupid propane question

hi1 · 14 Dec 2019

Bear with me once more. I have a condensing wall mounted French boiler. This is on a timer/thermostat is about 35 kw and heats about 15 rads. It also heats hot water stored in a 50 or thereabouts litre container. Its fed by a one tonne tank. the boiler is on for two hours in the morning at 20 degrees. in ten days it has used 10% of the tank capacity, about 100kgs?
my question is being is it possible for the boiler to work if say natural gas jets were installed instead of those for propane or is whats been used normal?

ianmcd · 14 Dec 2019

If your boiler had nat Gas injectors installed instead of LPG you would know all about it, your boiler would be in a terrible state

hi1 · 15 Dec 2019

Thanks for your reply. I can take it that its not jets. So would using 100 kgs of propane be correct usage for the time/ temperature and no of rads. I don't know what the calorific rating of propane is but when I used to have a natural gas boiler I cant envisage it using that quantity of gas over the same period although that was obviously measured in cu meters. how does a kg of propane equate to cu meters?

Madrab · 15 Dec 2019

Approx values as they can vary -

Cubic meter of compressed propane = 493Kg
Cubic meter of compressed Nat Gas = 128Kg

CV -
Propane (LPG) = 95Mj per m3
Nat Gas = 40Mj per m3

fixitflav · 8 Oct 2020

hi1 said:
Thanks for your reply. I can take it that its not jets. So would using 100 kgs of propane be correct usage for the time/ temperature and no of rads. I don't know what the calorific rating of propane is but when I used to have a natural gas boiler I cant envisage it using that quantity of gas over the same period although that was obviously measured in cu meters. how does a kg of propane equate to cu meters?

CV of propane, like most hydrocarbons above methane, is ~ 44MJ/kg.
Using 100kg in 20 hours, and assuming 90% efficiency, I make that boiler output 100*44*0.9/20 = 198MJ/h. At 3.6MJ/kWh that's boiler output 55kW. Seems on the high if the nominal rating is 35kW.

But that's assuming the 100kg is correct. Are you sure it's not 100 litre? The SG of liquid propane is about 0.6 so in that case the output is pretty much bang on.
Edit SG 0.6 was from memory, checked and as Madrab said it's more like 0.495

muggles · 8 Oct 2020

fixitflav said:
CV of propane, like most hydrocarbons above methane, is ~ 44MJ/kg.
Using 100kg in 20 hours, and assuming 90% efficiency, I make that boiler output 100*44*0.9/20 = 198MJ/h. At 3.6MJ/kWh that's boiler output 55kW. Seems on the high if the nominal rating is 35kW.

But that's assuming the 100kg is correct. Are you sure it's not 100 litre? The SG of liquid propane is about 0.6 so in that case the output is pretty much bang on.
Edit SG 0.6 was from memory, checked and as Madrab said it's more like 0.495

This thread is almost a year old, I expect it's sorted by now

Madrab · 8 Oct 2020

muggles said:
This thread is almost a year old, I expect it's sorted by now

Was going to say .... saw this post and thought .... I don't remember talking about LPG over the last few days

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stupid propane question

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