Re: CT Energy Price Patrol- Oil, Propane, Pellets, Alt. Fuels
I took a pic of my tankless hot water heater for you- it's a 199,000 btu unit- the largest Quietside makes (at least at that time). It's more or less the size of a bathroom medicine cabinet. I've had 3 simultaneous showers going with no problems... hot water and normal water pressure for all bathrooms.
Unfortunately, you can't use a smaller propane tank to get through a run out (at least that I'm aware of)... it's not like oil where you can dump a 5-gallon pail of diesel to get through... you really need to make sure the tank doesn't get below 20%.
A propane tank can only hold 80% of it's volume- so your 1000 gallon tank can only hold 800 gallons at max capacity. There needs to be space for expansion and contraction of the propane. There will be a dipstick in your tank that will read the liquid volume level in the tank... pressure is NOT an accurate measurement of how much is in your tank- the dipstick is.
The basic idea is that propane boils at about -44 degrees Fahrenheit, so you have pressurized propane liquid in your tank that gives off vapors when it boils. The bigger the tank, the more boiling surface area and the more pressure you can harness. As your devices call for vapor, it creates space in the tank, propane boils, and more vapor is formed, and so on.
In the case of a runout, in the old days of pilot lights... weird things would happen to your system when your tank got to under 20%.. with modern electronic ignition, it's not as big of an issue, but still a good idea to call for a propane delivery if the tank hits that 20% or below mark.
EDIT: The 2 main reasons that the little tank wouldn't work are that:
1) Since it is small, and understanding it can produce a tiny fraction of the vapor that your 1000 gallon tank can, it would freeze as it can't produce enough vapor to keep up with the demands of your propane appliances. The boiling process requires heat to make the vapor... if there isn't enough surface area to meet demand, the temp can get too low and literally freeze the tank... You won't have that problem with a large tank, but you will with a 100 pound or less tank (depending on the temp outside as well!). A gas grill needs only a small amount of propane as it needs a relatively low amount of btu's to operate... and that won't be the case with big appliances like water heater and furnace.
2) Your 1000 gallon tank is physically connected to your system in a permanent manner... it's not practical or really possible to make it "disconnectable" so you can attach a smaller tank.. it would create too many potential fail points and you want to minimize on leak points as best you can.
Hope I explained that well!?!
EDIT 2: Here is a video that might shed some light on the boiling concept. It might make more sense than my explanation (or at least clarify it):