Tankless water heater questions.

[MelissaW]

Hi friends! We've been going through all the old tankless hot water heater posts, but have two additional questions we couldn't find answers to there. First, can the tankless be vented through the same pipe that the old water heater used, or is the ventilation kit truly needed? Also, for those who swithced from a standard propane hot water heater to a tankless, did you notice a marked savings in propane? We are converting from a 40 gallon propane heater. Thanks so much!

[Alice In TX/MO]

No, a gas tankless heater needs a larger diameter vent pipe.

Don't know about the propane. We have natural gas.

[East Texas Pine Rooter]

I have an Aqua Star, natural gas, that the ignition is from a flashlight battery, I bought from Home Depot. This heater was installed 4-years ago, and I had it disconected this past summer. They have a 800 number you can get techinal advise from, and they had me try everything to take care of the problems I had. I would be taking a shower, and the water would just go cold. I had to turn the water off, and wait for the hot water. The other thing was you could hear the ignition sparking, but wouldn't ignite flame. It would finally light after many tries. My wife would have to stand beside the heater to tell me when it would finally ignite. They are supposed to work better in northern states, because of the cooler tap water temperatures. This is my second heater from this company, the first one was purchased from Home Depot back in the late 80's. This new one was suppose to be better. My plumber told me that the supply houses say to stay away form this brand. He has an electric, and really likes it, but they cost an additional $1,200 for the wireing requirements, after you purchase the water heater. I have gone back to a tank type electric heater.

[1eaglescout]

Its not the diameter of the vent that matters its the material. Tankless models require a satinless steel vent insted of a standad pipe. The heat that they put out is enough to melt standard class "B" vent.
I am a licensed plumber and a certified Rinnia {sp} tech. If you look at the temp rise chart that the manufacturers put out you will see why I have no time for any tankless.
You need to know that there are exterior mount models. They actually mount directly to the oputside of the house. In this application no vent is required. They are however venerable to a freeze situation. They MUST have 110 volts to work. {Read if the power goes out they won't work and may freeze and break.} The incoming and out going waterlines enter/exit the bottom of the unit. In my opinion this is dumbest thing about the whole unit. On the exterior mount units the pipes are exposed to the outside air.
Also, the gas supply line in your case is most likely not big enough. Tankless units require a 3/4 line as opposed to a 1/2 that most LP and Natural gas units require. This will be an additional expense. At the very least the line leading going to the heater will need to be upsized. Worst case scenario the the whole system may need to be reconfigured including the meter/regulator.

Melissa, If you want PM me and I will send you my license and rennia cert number. You can check those against the Ga seceratary of state web site and be sure that I am what I say I am.

[WisJim]

It depends on the size of pipe (and type) that you already have, and the size that the new wheater would require. Most people save enough money on gas to justify the cost of the tankless heater in a few years.

[MelissaW]

Thanks so much everyone! One of the best things about this forum is the availablity of good advice from people with experience! My husband asked me to post this, and I'm sure he will be eager to read your responses later today. I'd much rather hear the negative comments about the units now, instead of after spending $1000. The Aqua Star unit is indeed the one we were looking at. Eaglescout, I'm not exactly sure what a temp rise chart is. Is that something that I might find on the box, or at Bosch's website? What does the temp. rise indicate? Thanks for your expert advice! All I know is that the tank we have is 13 years old, and for some reason I can't even get a 10 minute shower without the water turning ice cold. Obviously something is wrong!

[seedspreader]

Originally Posted by MelissaW

Thanks so much everyone! One of the best things about this forum is the availablity of good advice from people with experience! My husband asked me to post this, and I'm sure he will be eager to read your responses later today. I'd much rather hear the negative comments about the units now, instead of after spending $1000. The Aqua Star unit is indeed the one we were looking at. Eaglescout, I'm not exactly sure what a temp rise chart is. Is that something that I might find on the box, or at Bosch's website? What does the temp. rise indicate? Thanks for your expert advice! All I know is that the tank we have is 13 years old, and for some reason I can't even get a 10 minute shower without the water turning ice cold. Obviously something is wrong!

If y'all are on fine Ohio hardwater like us, it's probably filled with sediment.

[MelissaW]

You're probably right. I know that DH has drained the sediment out several times over the years, but since it's getting old, we felt like this was a good time to look into the tankless since he's always been interested in them. I'm a little disappointed that so many people have had problems with them. We were really optimistic that changing over could save on propane. Same water as you, though! Before treatment you'd have to drink it with a knife and fork!

[YuccaFlatsRanch]

"I would be taking a shower, and the water would just go cold. "

The reason for this (and it happens to me in the summer when using rainwater from rainwater tanks) is that the water coming in to the unit is warmer. The unit heats and the temp is determined by the flow of water. There is an overheat switch that senses the temperature of the water. If you have warmer water going in at a particular flow rate the warmer water gets heated past the cutout temp of the overheat switch and the propane/gas is turned off. Two solutions - cooler water coming in or a greater volume of water being used so it doesn't heat as long. Turning on a faucet along with your shower will do the trick. We plumbed our shower with 2 shower heads (very low flow) and running both solves my problem.

[LisaInN.Idaho]

We have a Bosch Aquastar and love it. We're far north so we've never had the temperature problem. The only problem we've had is in extreme cold, we have had the cold air come down the flue and freeze the unit. Now we just run a fan that keeps the heavier cold air out.

[MelissaW]

Well, if warm water is what causes the unit to work improperly, that shouldn't be a problem here. Our water is extremely cold, probably due to having a deep well, and living in a cold climate. There is a holding tank coming out of the well, but it is in the basement, and stays cool even in summer. I hope that East Texas Pine Rooter has a better time with the new tank. What a shame the investment didn't work out.

[Jane in southwest WI]

We've had our Bocsh Aquastar since 2001 and never had any problems with it. Water is always hot, as much as you want and when you want. It is cheap to run on propane, too.

[SolarGary]

Originally Posted by 1eaglescout

If you look at the temp rise chart that the manufacturers put out you will see why I have no time for any tankless.

Hi,

Could you explain what you mean here. Are you saying that the temperature does not come up fast enough when the unit first comes on? Or, that it does not deliver enough hot water?

Gary

[Andy Nonymous]

Gary, he means the "temperature rise per gallon, per minute". A standard gas fired water heater is fired at about 30,000 to 50,000 btu's per hour, whereas the tankless heaters fire at about 100,000 or more, making the flue gases a lot hotter, hence the recommended stainless vent pipe rather than the aluminum lined "b" vent which is fine for a standard water heater.

Yes, incoming water temperature being 'too warm' will make them shut down, and units without a standing pilot may have issues with ignition from time to time. My own take on it, after having installed and used a few, both gas and electric (at others houses), don't get an electric unit - the flow rates are very low; don't oversize a gas unit: not using enough hot water quickly enough will cause wild fluctuations of temperature as it goes between 'heat' and 'over heat'; if you use hot water frequently, get one with a standing pilot, as the savings in gas won't make a difference compared to the flow time (and water loss) of waiting for ignition.

And Mellisa, if you are dealing with a gas water heater, it is full of sediment, If an electric water heater, either it too is full of sediment AND / or the bottom element of your tank is burned out, leaving only the top element heating water, and hence about 8 gallons of hot water in the tank. The way the electric tanks work: in a tank of cold water, the top element heats the top water first, and when that is satisfied, it transfers the 240 to the bottom element which then does the bulk of the work heating the rest of the water (and far more of the time), whereby if your usage exceeds the capcity of the bottom elemement to keep up, the top element, having to heat only the top water of the tank can keep up easier, and you won't run out - in theory anyway.

Andy

[Hip_Shot_Hanna]

We just installed a Rennai tankless water heater, and we are quite happy with it. Rather, we had it installed by the fellow that did the retrofit to propane from electric water heater and electric cookstove. We find that it seems to be very economical to run. We had it installed on an outside wall in our utility room and vented it through the wall.

[hoofinitnorth]

We have an *oil-fired* on-demand hot water heater - Toyo. We really like it and it keeps up with our 2,000+sf house just fine.

[1eaglescout]

What I mean by temperature rise per minute is the rise in the water temperature before it enters the heater to when it leaves. For example, many tankless manufacturers advertise 30-40 degrees temp rise. During the summer water around here is between 70 and 80 degrees. With the temp rise that leaves you with between 100-120 degree water. In the winter the water is between 40 and 50 degrees, you do the math. You can probably find a temp rise chart on the websites for each manufacturer.

Melissa, well water actually stays warmer in many cases than county water. Wells are obviously deeper than a water main. The radiant heat from the ground keeps well water warmer than the water in relatively shollow water mains. Think of a cave.

As far as BTUs the 50 gallons A.O, Smith heater in my basement is rated at 40,000 per hour. The Rinnai I was working on this morning is rated at 199,000. The reason they rated at 199,000 is because any unit rated a 200,000 BTUs or more is considered a boiler. A boiler requires a seperate license.

Rinnia by the way does NOT recommend one of their units to be installed in a house that is supplied with well water UNLESS a water softener is installed as well. The minerals that well water contains will cause a scale build up on the inside of the copper heat exchanger/storage tank.

As far as the idea of fuel savings paying for the added expense of the unit, that is a fairytale. Rinnai figures that at the current price of natural gas it would take 30 years for the unit to pay for itself. They expect the service life to be about 20 years.

Granted, water conditions and temps vary across the country. This is what I was told in the cert school and what I have learned from repairing the units.

[sulix]

I installed a Bosch Aquastar water heater in place of my electric 50 gal water heater.Have used it for 5 yrs.Used galvanized exhaust.which is run out at an angle only about 3 ft above the old cellar window outside.No down draft,3/4 copper gas line...Never run out of hot water.Never too hot in summer.It has paid for itself in less than 3 years and i am extremely happy with the performance.
Even with the hot summer days here in S.D.and all the wind i have never had a failure or water which is too hot to use.
Although the only downfall i have noticed..My old celer which it is installed doesn't have any heat to keep some of my canned goods from freezing.This has only happened once for a short time