Faith,

A tankless heater with an energy factor of .82 uses about 38% less gas to heat the same amount of water as a tank unit does.

The LP company is misstating a fact. A tankless heater uses a large volume of gas at one time - which speaks to the size of the gas supply to it. But the overall use is less.
There is another issue or problem here and I don't know what it is.

A tankless water heater takes about 2 seconds to get fired up. It also doesn't keep hot water in the first 10 feet of pipe like a tank heater does - that adds another second or so to the wait. All told, a tankless heater can add about 3-4 seconds to the wait for hot water -- not 5 minutes.
Why is it taking 5 minutes?

You really need to do the math to find out what the real issue is.

What else is using gas? Are you using an inordinate amount of hot water? How much a gal is your propane?

My guess is the long wait is due to bad plumbing design - like having the heater far away from the point of use. I'd also look to see if the pipes are insulated.

A circ pump will help with the wait and reduce water use, but will increase the amount of propane you use.

I only use the gas for hot water and for my dryer 3 loads a week. I do not use a lot of hot water as there is only 2 of us. The cost goes up in the winter and last month was 2.39 a gal and it said I used 177 gal last month. When I called the propane place they checked for a leak and said it was the tankless water heater as it takes a lot of gas and is a problem for alot of people who have the tankless. It sounds like I need to have a plumber out to check the things you mentioned above. Thanks for your advise.

Well, let's do some math:

177 gal of propane at 91,500 btu's per gal is 16,195,500 btu's.

Since your tankless water heater is about 82% efficient, we will multiply that by 0.82 and get 13,280,210 usable btu's.

It takes 1 btu to raise a pound of water 1 degree Fahrenheit and a gallon of water weighs about 8.35 pounds.
Assuming that you increased the temp of the water from 50 degrees to 110 degrees (typical shower is 105) you would multiply 8.35 (weight) x 60 (degrees) and get 501 (Which is the number of btu's to heat one gal of water 60 degrees). (Note: it doesn't matter that your heater is set for 120 degrees, you mix that down to something like 105-110 degrees)

Divide the 13,280,210 by 501 and you get 26,507 gallons of hot water heated to 110 degrees. Something tells me you didn't use 26,500 gallons of hot water in the month. Granted, I didn't include an allowance for the clothes dryer... but I don't think we are even close.

Do you have a water bill that will tell you what you used in water overall for an average month?

The average water usage in the US is 60-70 gal per person per day. At the high end that would be 4200 gal total water consumption (hot and cold) for the two of you in a month.
All of your water usage combined doesn't come close to the 26,500 gal number.

Let's look at it another way. Remember I said your water heater was 82% efficient? Well, let's assume you use the average 70 gal of water a day per person. Let's also assume that 1/3 of that is hot water (wild guess). Your water heater would have to be somewhere around .04 percent efficient for the numbers to work. That's simply not possible. The worst water heaters are about 63 % efficient.

As you can see, something is very, very wrong. I think it's physically impossible for you to use that much propane in a month unless you have a leak.

Faith,

One more question... what is your heat source? Are you sure that you aren't using propane to heat the house?

Perhaps you just got the bill for a tank fill

Good point ZL700, I was assuming that we knew that the 177 gal was actual usage.

yeah something is totally off with the OP...
when I converted to a tankless LP water heater the savings were unbelievable. These things rock!

that putting in a recirc pump would save energy is very debatable - copper pipe is a good radiation and a fair amt. of energy would go into heating your house

Good rule of thumb that will offend many here: never rely on an oil co. for advice on which oil boiler to use and never rely on a propane co. to tell you what to do with the propane they sell. Hint hint: they'd love to sell you more!

Our gas tankless water heaters take 5 minutes to get hot water. A pain for sure. Rinsing dishes is a pain too with the cold sandwich factor.

well "heaters" implies you have more than 1. They are so small, why didn't you just put one near the kitchen and the other near the bathrooms?
I think some people are not installing these sensibly, in this country at least. A house where I lived one summer in England - this was in the mid 90s(!) - had one installed in the kitchen and one near the bathrooms. Endless hot water was quickly available, anywhere.

iceqween13,

I would guess that your tankless heater doesn't take 5 minutes to get hot - it takes about 3 seconds.

Perhaps it takes you 5 minutes to get hot water - but that's not the water heater's fault.

A 3/4" pipe that's 50' long will take about 2.5 minutes at 2 gpm to move the cold water out of the pipes. That is where the real problem is.

Be sure that the hot water lines are insulated also.

davidrt28:"well "heaters" implies you have more than 1. They are so small, why didn't you just put one near the kitchen and the other near the bathrooms?"

Yes, we have more than one - because one heater alone was grim. We have large, expensive units - Noritz 0751 - 199,900 btuh each. Did the place you stayed in England have a jacuzzi, 4.5 cu ft. washer, dishwasher, etc.? I don't think a person can compare.

I agree jake2007 - It doesn't take 5 minutes to get hot - it just takes that long to get it to the faucets.

The point that I'm making is that people blame the water heater when it isn't that at all. The OP did the same thing.

In many cases it's simply poor design. The heater is at one end of the house and the master bath is 60 feet away. There's no circ pump, sometimes no pipe insulation, etc.
My first choice would be to get people to stop building ridiculous McMansions in the first place. I read about couples (empty nesters and small families) with a 3200-5000 sq ft house - big tubs, multi-head showers and such. What the hell is the point in that?!? People don't know what to do so they build a bigger fire.

Second choice, if they insist on being stupid, would be to get better house design that's more compact.

Last choice for people who insist on both gluttony AND bad design is remediation.

I think that you are in the "remediation" category.

In high demand situations I would combine a tankless with an insulated tank.

A solution for bad design where the heater is far away from the faucet is a small electric Point of Use in series with the main water heater.

"A 3/4" pipe that's 50' long will take about 2.5 minutes at 2 gpm to move the cold water out of the pipes."

This is not mathematically correct: The volume of water in 50' lineal of 3/4" pipe is about 1 gallon.

Does the water heater ever display error codes or have to be reset? A faulty ignitor or sensor could be responsible for the OP's complaint of high gas bills.

My tankless water heater had this problem (or rather symptom) for a while. I noticed something funny when I was on the roof replacing shingles and got a big whiff of gas coming out of the exhaust flue. Someone inside was running the hot water and the heater was trying to cycle on, but the gas was just blowing right through. We had been experiencing problems with the unit not heating up promptly, or heating for about 5 seconds and then going out. Sometimes the heater would trip and send an error code, requiring a manual reset.

This smell of gas on the roof got me thinking maybe the heater is having trouble igniting? Luckily the guy helping me with the shingles was not a smoker, or i may have discovered the problem under different circumstances.

After extensive troubleshooting, it turned out the main burner was partially clogged with dust. The dust was mostly accumulated around the sides of the burner, where the sensor and ignitors are. The heat from the flame was not getting to the sensor, especially when the burner was running at low or moderate flame. Only high flame created fire wide enough for the sensor to detect. The dust had also partially obstructed the ignitor sparks from the flow of gas, resulting in the smell I noticed on the roof.

The symptoms were caused by the heater's safety override feature. If the sensor does not detect flame after several seconds of delivering gas, it kills the ignition and starts over. Same thing if the spark does not ignite the gas. My gas bill skyrocketed during this episode, even though it was summertime. I mean we had like a $100 gas bill in September when $20 is normal.

I fixed the problems with the heater, took it apart and blew out all the dust. I installed an intake vent to draw fresh air directly into the unit without mixing in garage dust. Then I put a 5 gallon electric heater in line directly after the tankless. I keep the electric unit turned down to 110, and the tankless turned up to 130. This keeps filling the small tank with 130 deg water. The comfort factor is 100%. There is no shot of cold in the hot water line when you turn a faucet off and back on. For my small house, the one small tank right next to the tankless is perfect. There is about 50' of run to reach the master bath, but no problem. Hot arrives in about 30 seconds if the pipe is dead cold, and that is at a flow of 2 GPM.

thanks for the support Jake

"A solution for bad design where the heater is far away from the faucet is a small electric Point of Use in series with the main water heater."

This is exactly what I did in my house, where I have only 1 199k btu tankless unit. I have a small electric unit in the kitchen because it is far away from the bathrooms, where the tankless was installed.

I'm sorry, I know that I was a more than a little harsh.
It does gall me how spoiled, wasteful and entitled we've all become though. It's like complaining about the defective garage when the boat and the hummer don't fit with plenty of room to open the doors all the way.

Yes, your rant was a little harsh. And presumptuous.
We have 3 bedroom house - 2300 sq ft house. Not a McMansion. It's amazing how strong people feel that everyone should love these things. I don't. And people should be aware of what they're getting into. Not everyone is smitten with them. I still think people are $ ahead in keeping their electric hot water tank. They are costly to purchase and install. And not for everyone.

My house is roughly the same size and I'm incredibly satisfied with my purchase - and I only have 1. I have no doubt at all that in a few more years I will totally recoup the cost of the investment. Different strokes for different folks as the cliche goes.

I do know people who have been unhappy with them though. But again it has more to do with the way they are installed.

Math is math. They use less energy, and therefore they are cheaper to operate in most cases than electric HW tanks. That's why the people at the DOE who have degrees in physics give a tax credit for them and not for electric tanked water heaters. Maybe if you live in a place where propane or NG is incredibly expensive they wouldn't be less expensive.

I have to admit, these tankLESS threads are getting... less bad, and calculations getting more accurate... but...

Oh Dear Gawd... Yet Another tankless thread lacking two PRIMARY PHYSICAL parameters (before we even get to utility cost$$ in YOUR area) which DETERMINE whether tankLESS will work for you, and how hellish/extra hassle it will be, to wit:

LOWEST INCOMING (winter) WATER TEMPERATURE;
and
Incoming water HARDNESS (Impeller Liming, anyone?)

Can we simply adopt a policy of automatically asking the OP of any tankless thread to supply at least these 2 data, at minimum?

PS: That partial failure mode (and MAJOR GAS WASTAGE) described by aidan_m is downright scary. All the moreso because few plumbers would even be able to diagnose it, and, of course, the propane company has no incentive at all to solve it. =:O