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Just looking for ideas.

We have got a static caravan but with no electricity available but want to try and run a boiler for heating radiators. Any ideas of how to get power to the boiler which will keep it running for a while. I thought of a 12v 120ah battery connected to 800w inverter to supply boiler with 230v. Any idea how long the battery would last running the boiler for. Or any calculations that would help understand how long it would last. Also thought of adding a solar panel through a charge controller to trickle charge the battery but as its winter probably would make much difference. We have a generator but don't really what to be running that all the time.
 
Googling conventional gas boiler consumption gives (very) approximately 200watts mains power (I assume mostly from the pump?).
Converter efficiency say 80%
So say power required from battery is about 240 watts, equates to 20A from 12V battery (while boiler runs).
So your suggested battery would last 6 hours, boiler running continuously, if battery lives up to its rating.
But your boiler might be cycling on/off, so could last longer.
Probably not more than a day though.

Warning - just my thoughts - no personal experience of this.
 
Or a wabasto or espacher, diesel boiler

Small size , heat water for radiator loop, work very well i have few friends with them on canal boats

they are also 12 or 24 volt, and consumer less electrical energy than a conventional boiler

you can also have a separate small plastic tank for them and as it is not used to move the vehicle, it can be filled with red diesel
 

Lucien Nunes

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The two biggest loads in a domestic C/H system have traditionally been the circulating pump and the flue fan, but modern electronically controlled pumps can now run at a few tens of watts instead of nearer 100W. So it is quite likely that a smaller boiler and pump could be run on 100W total at 230V AC when fired, dropping to perhaps 30W when circulating but unfired.

As mentioned above, vehicle and marine heating systems can use less. Smaller Eberspächer and Webasto diesel-fired central heating units up to about 7kW come in at 10-50W electrical load, i.e. 1-4A at 12V, most of the load again being the burner fan and the circulator. Units up to 12kW are typically in the 50-100W ballpark. Like the domestic boiler it will have a lower consumption when unfired, although a smaller heat input will mean a higher duty cycle so the electrical consumption might not be much less.

For LPG (Butane or Propane) the Alde 2030 (5.5kW output into water) uses only 18W (1.5A at 12V). Its predecessors, the tall thin 29xx series boilers that were popular in caravans in the 90s and 00s, used a mere 4- 6W just for the circulating pump, as neither the burner nor the thermostatic gas valve required power.

Regarding the relative cost of red diesel vs. LPG, the actual fuel cost was about 50-60% the last time I looked, although diesel-fired heaters typically require more maintenance.
 

PEG

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No surprise that Lucien has covered the question nicely😊
I will only add,that battery sizing,needs to take account of not depleting your stated Ah rating beyond 50%,and that more modern boilers and heaters of the Webasto,Eberspacher,etc type,have low voltage threshold,included in their control system.
 

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