Hello, Tiny4me76...
Your question is a broad question and answers you will get may, and will, vary. But in general: Today there are many models of tankless water heaters on market. Among the best and the most popular are Rinnai, Takagi, Noritz and Rheem. I personally consider Rinnai the best tankless heater. I have 2 Rinnais in my house since 2002 and I could not be happier.
To the contrary of the popular believe, tankless heater are not new product on market but have been around - at least in some form - for over 70 years. It is a proven product that is being continuously improved as technology advances.
Tankless heaters come in different outputs. The small units produce about 5 gln/m while the big units produce over 11 gln of hot water per minute.
Tankless heaters are manufactured for interior installation and for exterior installation. The heater itself will run from about +/- $700 up to $1,300 a unit + other parts you will need to properly install them.
If you select interior installation you will need dedicated, double wall, vent with dedicated roof cap. You cannot get any other vent but vent designed by the manufacturer for this heater. Even roof-jack is dedicated and has to be used to properly attach the termination piece. This vent is not cheap and has installation limitations as well. You absolutely cannot use existing vent that serviced your conventional hot water heater.
If you select tankless heater for exterior installation, you will probably want to purchase dedicated enclosure to shelter the heater and all plumbing connections from the elements. If you add full port gas flex, Watts water installation kit and electrical supplies, you will easily add $300-$400.00 to the cost of the heater.
Tankless heater requires dedicated electrical switch. This usually doesn't present any problem but this expense must be taken in consideration as well.
The most important is gas supply. Tankless heaters have variable gas consumption ranging from 18,000 up to 200,000 Btu's. In other words, the heater itself uses more gas than your entire house. In 90% of cases, we have to run new gas line of appropriate size from the gas meter all the way to the heater. Depending on the distance, new gas line can run you another +/- $500.00
You select size of the heater according to the size of your house and number of people living in the house. The most popular model we install is Rinnai 94 LSi. ( 9.4 gln/m flow ). With low flow shower heads installed, 9.4 gallons per minute flow proved to be the most requested model by our customers.
I recommend that you call few professionals to see your house and to give you idea what your installation will require. I am sure you could do the installation yourself but to assure the heater is installed properly, I would suggest that you let a certified installer to do the job.
As far as the cost of installation goes: it varies depending of how much work needs to be done to convert old system to new heater as well as if you need new gas line and vent. But figure no less then $560.00 for the most optimal situation and higher...
I am enclosing 3 photos. 1st one is a Noritz tankless heater without enclosure and installed by the homeowner. The photos 2 and 3 show our installation in 3,000 + sq. feet house. In this case, it is a Rinnai heater installed inside an enclosure with all required flush valves, shut off valves and pressure valve. As you can see from the photos, enclosure makes for cleaner installation.
I hope this information will help you to make an educated decision. Good luck and let us know what you decided to do. Milo
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