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Old 07-28-2008, 08:25 PM
 
193 posts, read 491,650 times
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I have tried about 5 different google searches and haven't found an answer yet. Maybe one of you know the answer, or can point me to an online calculator of some sort.

The situation is this, I recently moved and am going to be using small propane tanks (probably 5 gallon tanks, but maybe 7) for my hot water heater (I'm doing away with the gas stove that only partially works, and switching to counter top appliances, since we only "cook" once a day usually, and small meals). I'm curious to know whether there is some formula for finding out how much propane I will usually use. I will probably keep the hot water heater on all the time, and it will be set at medium or a little bit higher.

The water heater has a 30 gal tank and was made in 2003. Also, I'm curious as to whether it makes any difference in fuel consumption where the propane tank is placed (does distance make a difference).

Also, while it would be more convenient to have it on all the time, I wonder if it is more fuel efficient to turn off when gone for a couple days, or whether it uses more to do the initial "heat up"?

Thanks!
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Old 07-28-2008, 09:18 PM
 
Location: Central Texas
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I don't know that I can answer your question, but we use propane for hot water, cooking, and heating. We have a 200 gallon tank, and in the summer, when we're not using it for heating, we have it filled once in the spring (about April), and then again in September. In the winter, of course, we have it filled more often.
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Old 07-28-2008, 09:34 PM
 
Location: Oswego, IL
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The burner input will determine how long a tank will last. The 30 gal heaters I looked at were 30,000 BTU per hr. The BTU output of 1 gal of LP is about 20,000 per pound and 2500 per cu ft. Something to remember with LP is that it is stored as a liquid and used as a vapor. This means the liquid in the tank needs surface area to absorb heat and vaporize. You don't say what part of the country you are from. If it gets cold you will need a vaporizer. A little LP powered burner to heat & boil the liquid. I would not try to feed it with small tanks. There is not enough surface area to vaporize enough to provide a constant supply. This link gives you more numbers

Properties of LP Gas

Forgot about the distance question. Because LP operates at a much higher pressure than Nat Gas it can be piped and then pressure regulated. Because of this distance is no problem.

Last edited by studedude; 07-28-2008 at 09:37 PM.. Reason: add material
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Old 07-28-2008, 10:52 PM
 
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Thanks for the advice (which kind of worries me!). I know someone who had a similar mobile home in the spot where mine is now, she used 7 gal tanks (one a week, but not sure if she used it for cooking in addition to hot water), though I'll have to ask her if she had problems with the cold & surface areas and such. It does get *very* cold here, most days in the winter are below freezing and nights can get to below zero. We're at over 7000 ft in Northern NM mountains.

We've had gas lines freeze at our previous place, in addition to other amusements such as water & sewage pipes freezing.

I know one person who used one 5 gal tank for her stove and another one for her water heater, keeping the tanks inside and turning on only when in need.

I don't really know for sure how hot water heaters work, I always assumed that they turned on fully to heat the water up, then when it was the right temp. they turned down to keep it at the temp. When mentioning 30,000 btu / hr is this refering to all the time usage or only to initially heat up water and touch up when new water comes in?
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Old 07-28-2008, 11:00 PM
 
Location: Apple Valley Calif
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Why do you want to use such a small tank? You will be filling it often. Call your local propane vendor. You will find they will drop a larger tank on your property for no charge, as long as you are using and buying fuel from them. then you can fill just a few times a year, at most.
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Old 07-28-2008, 11:08 PM
 
Location: Oswego, IL
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Most hot water heaters are either on or off. They come on and heat water to thermostat setting. When water cools, from using hot water and refilling heater with cold or water cooling from sitting unused, it turns on again until thermostat is satisfied. The only fuel that is used when not heating is for pilot if your heater has a standing pilot. Keeping LP inside is not a good idea. LP vapor is heaver than air and if there is a leak it will "pool" in any low area. Liquid will expand to 270 time its volume when vaporized. Any spark or open flame can cause an explosion.
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Old 07-28-2008, 11:13 PM
 
Location: Knoxville
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I agree, why use such small tanks and spend all your time re-filling them. The gas you use driving down to get them filled will more than offset the use of a larger tank.

Distance is not an issue.

A propane water heater burner goes on when the temp of the water drops below the set point. The burner is really on or off. yOu can conserve the temperature of the water in the tank with an insulated blanket, however, the newer water heaters are so well insulated, they actually tell you not to use a blanket.

Not sure I would want to store propane tanks inside the house.

I've never heard of a gas line freezing, but I guess it could if it was cold enough for long enough. YOu could turn the thermostat down to pilot or "vacation" except when you want hot water, then turn it up. Most water heaters will heat the tank up in less than an hour. If you can plan your usage and live with the delay, you could save a lot of gas. ON vacation, the tank will keep the water warm for a long time. YOu will just have to play with it and see how it works in your climate.
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Old 07-28-2008, 11:28 PM
 
Location: Apple Valley Calif
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It is illegal to store a propane tank in any building, residence or not. The law was made for a reason. DON'T DO IT...! Extremely dangerous..........
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Old 07-28-2008, 11:33 PM
 
Location: Lake Forest, CA
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You seem like a candidate for a tankless water heater. In most countries outside the US, tankless water heaters are used for heating water for short periods of time for bathing or washing dishes instead of trying to keep a 30+ gallon tank of water heated up 24x7. When I lived in South America for a few years, I had a small portable propane tank (approx 5 gallons) OUTDOORS, just outside the kitchen that was chained up to a post (along with one spare 5 gallon tank that was connected as soon as the first one ran out). It was connected to permanent hard line gas pipe to a two burner stovetop in the kitchen. It also fed a tankless wall mount water heater in the kitchen, that provided hot water to the kitchen and bath faucets, and to the washing machine (also in the kitchen). It had a self igniting pilot so it didn't burn propane when not in use. In a one person household my 5 gallon propane tank lasted 10 to 15 days for hot water and cooking (not whole house heating). After my first tank ran out I could get it refilled a few blocks away and then it became the next spare. This simple system is used by hundreds of millions of households around the world who don't have access to utility gas pipes or who don't have large fossil fuel needs that require a delivery truck.
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Old 07-29-2008, 01:00 AM
 
193 posts, read 491,650 times
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Thanks for the tips & advice. I am actually looking into a tankless water heater. I thought the cost would be prohibitive however I've found a couple of electric models for around $200, not sure whether I'll go with one of those or not though.

I can not afford a large "typical" tank because the propane companies out here (and in most places I've heard) have high minimums to what they'll fill. I can understand this from their viewpoint of labor/travel expense, however I know people with regular tanks who easily spend $700 to have their tanks filled, and usually need them filled twice per winter. Though they are people who are heating with propane, I will just be using it for hot water.

It's not too big a deal to fill the small tanks, I go to the area where propane is sold usually once a week, and if I have two tanks I can switch them out when one runs low as was mentioned by someone else. I wouldn't want to make a trip *just* for propane, but if I'm going to town anyhow. I would actually prefer a 100 gal tank however I do not have a truck and don't think it would transport very easily in my Subaru =) .
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