tankless hot water heaters

Toolmaster · 12-03-2009, 07:28 PM

OK, first time installing a tankless on a house, How do I know what I really need, someone recommend a takagi-JR. The house will have 2 1\2 baths, one with a double bowl sink, and a gas range. Can this heater carry all of that. Looked It up and some of the specs have me asking questions. First, what are BTU's second what is W.C. you guys don't laugh at me, still young and haven't really messed with gas before

thanks.

majakdragon · 12-04-2009, 09:29 AM

While I always promote DIY projects, not all are good choices for those without experience. This is especially true with gas lines. You need to know how to size gas lines for volume so you don't "starve" the fixure using the gas. Anther problem is any warranty for the Tankless heater may be voided if not installed by a licenced person. BTU's are a measure of heat produced and WC is "normally" a Water Closet (toilet). Since i cannot see the instructions, I am at a loss to figure out what you need. This sounds like a new house or major remodel and may require a permit.

jerryh3 · 12-04-2009, 09:34 AM

WC should be water column. A measure of pressure. This definitely not a starter project. I think you should sub this one out. I hope this is for your own house and your not even thinking about doing this in a customer's house.

md2lgyk · 12-04-2009, 11:01 AM

We installed a gas tankless heater in the log house we're building. Most manufacturer's websites have information on how to pick the right size. Based on information I found there, I picked the size and installed the unit myself. I had the gas company do the gas line.

One other thing to consider carefully is how the heater will be vented. Not only for safety, but also because the vent piping is quite expensive.

**beenthere** · 12-04-2009, 11:30 AM

As earlier. WC is water column. And is generally referring to the gas pressure to the unit and manifold.
BTU is British Thermal Unit. Its a measurement of heat.

Yoyizit · 12-04-2009, 12:24 PM

Quote:

Originally Posted by Toolmaster

How do I know what I really need

50 to 200 gallons per person per day, with 120 being average and with ~half of that being 120F hot water.
It takes 8.3 BTU to raise one gallon of water 1F.
Your incoming water is ~50F.
BTUs measure energy, and the rate of consuming energy = power.
100,000 BTUs = 29.3 kwh, or 100,000 BTUs per hour = 29.3 kw.

jerryh3 · 12-04-2009, 12:26 PM

Quote:

Originally Posted by Yoyizit

~100 gallons per person per day, with half of that being 120F hot water.
It takes 8.3 BTU to raise one gallon of water 1F.
Your incoming water is ~50F.
BTUs measure energy, and the rate of consuming energy = power.
100,000 BTUs = 29.3 kwh, or 100,000 BTUs per hour = 29.3 kw.

Is all of that assuming 100% efficiency?

Yoyizit · 12-04-2009, 12:28 PM

Quote:

Originally Posted by jerryh3

Is all of that assuming 100% efficiency?

It comes from here
http://www.onlineconversion.com/
but I guess tankless units run at near 100% efficiency.

pyper · 12-04-2009, 09:41 PM

WC also means "water closet" in Europe. In other words, a bathroom.

I have a tankless heater, but I don't recommend it.

If you don't understand how to install it, then it's definitely not a DIY project. In my case they needed to put in a new vent/chimney, and a new gas line. It was a big project.

It doesn't work as well as a water heater should, and it uses a lot more gas than I expected.

**beenthere** · 12-05-2009, 06:42 AM

Quote:

Originally Posted by Yoyizit

It comes from here
http://www.onlineconversion.com/
but I guess tankless units run at near 100% efficiency.

Electric are 100%. But you can get 80% efficient tankless in gas fired units.

pyper · 12-05-2009, 06:59 AM

Nothing is 100% efficient. But maybe it can round up.

To me, it doesn't matter how "efficient" they are as much as it matters how much energy they use in the course of a year. A standard water heater has a 40,000 BTU burner that runs 15 to 30 minutes a day. A tankless heater has a 250,000 BTU burner that runs whenever you turn the hot water on.

**beenthere** · 12-05-2009, 07:08 AM

There is 3.413 BTUs to a watt.
So for every watt an electric heater consumes. You get 3.413 BTUs of heat.

pyper · 12-05-2009, 07:33 AM

Quote:

Originally Posted by beenthere

There is 3.413 BTUs to a watt.
So for every watt an electric heater consumes. You get 3.413 BTUs of heat.

There's a difference between the physical efficiency of the heating element and efficiently using the heat produced.

**beenthere** · 12-05-2009, 07:40 AM

Quote:

Originally Posted by pyper

There's a difference between the physical efficiency of the heating element and efficiently using the heat produced.

All the heat the element produces. Will be absorbed by the water(talking electric water heaters, or boilers).

On electric heating elements used to heat air. As long as the element is not allowed to get hot enough to glow. You still get 100% of the heat.

Now if your talking about delivering that heat to an area. That is distribution efficiency. And is another topic itself.

Yoyizit · 12-05-2009, 12:34 PM

Quote:

Originally Posted by beenthere

Electric are 100%. But you can get 80% efficient tankless in gas fired units.

I don't like 'em.
The ones in Germany were clicking all the time trying to keep up, and in three weeks I never got to take a shower without at least some cold water dumping on me.