I checked out Rinnai. Look like high-end units, and they indicate prices are $900-$1400--which is not too bad...3x-5x what a typical electric 50 gal. heater costs but you are not storing water, so sooner or later is a payoff.

I have 50-51 degree water at the street, running about 95-100 psi. Everyone's situation will be different--not so much with the temp, I'm betting, but probably with the pressure.

I keep my H/W heaters (got 2) at factory settings which is about 120 +/- degrees. And I'm no scientist, but I'm thinking a person would want about 3-4 gallons per minute of hot water when showering/bathing, washing clothes. There is probably graphs and charts on this subject (GPM requirements), so I am guessing.

Given that, look at this:

http://www.rinnai.us/documentation/downloads/R75LSe_SP_UC.pdf 

This unit looks like it would work for me. 4GPM with 70 degree temp rise--perfect! Would yield 120 degree water with real good volume. But if you look at the heading "min/max water water supply pressure" it appears that the unit performs best at high line pressure, perhaps something on the order of 50-60 psi would be necessary for my needs (there IS some gaddam science involved here!) but while I tested my copper pipe at 125 psi after I topped out, I'm not sure I would want to run the braided/flexible under-sink supply lines, and washing machine supply's, at that pressure. Damn things seem to break when you are gone--but I do know that upgrade, higher pressure supplys are available...

I'm just thinking out loud here, but what I'm thinking is that a person would have to do some thinking on this from multiple angles before making the plunge (lol! I got 'plunge' in when talking about water!).

if you live in a warmer part of the country, tankless work well. If you have cold winters, you will need a real high-end unit or you wont get enough volume. During the winter my incoming water of the street is around 38 - 40 degrees.

Not a joke.

I am many things but I am not a plumber or electrician. I got pretty much everything else covered.

Instead of loosening a supply line ( which I know I will end up with a leak if I do that) can I just pop that pressure valve thingy?

And, something else that could have a big impact (on the positive side) on on-demand units:

I have noticed that I only open the hot side of my faucet valve part way when taking a shower (don't get any ideas TDub), so shower water is mostly hot and some cold. I suppose a person could use all hot, no cold which would reduce the temperature rise necessary, which would increase the gpm output, and possibly reduce the needed increase in psi...quite a bit to think about.

I'd really like to live with one of these units before I bought one--fat chance and lol.

I'd also like to see some energy usage charts estimating annual costs--these things may not be trying to keep 30-50 gallons of water hot, but when they 'work', they work damned hard.

Fuzz,

The main factors to consider/figure out in a tankless are:

1. The temperature of your water in the ground (incoming).

2. The flow rate (GPM).

3. The cost of installation. The expensive part (besides the unit) is the required ventilation.

4. Cost of Natural Gas in your area. If you are considering going tankless with electric, I assume money is no object, and you overbid on cigars.

Don't go less that 100,000 btu unit.

JHC, no, you need more volume of air than that to get the tank to drain well, i.e., other than a trickle. Are you sure you really need to drain the tank in the first place? Is it gas or electric? We don't use gas WH's here too much, but I think it would be a little more important to keep them (burner at the bottom) clean than,say, electric (with elements shoved in the side).

It is electric. I thought I heard that if you drain the rust out once a year they will last forever. It has been 4 years. Thought it would be a good idea.

As far as loosening the supply lines...there are two lines coming in to it and they are both soldiered or glued together.

there must be some sort of connection arrangement that allows the R/R of the heater...I would hope...

If you are not 'mechanical', mebbe best to call someone in. And do not feel bad about this sort of stuff--I have a friend who barely knows which way to turn a door knob to get it to open, but he is a major influence on my vision of what a near-perfect parent is.

we all have something

NEVER....I can fix anything. And I never need directions.

OK, I just disconnected the big pipe leading from the street to the house. I think I am good to go. The neighbor kids are having fun in the "sprinkler".

Chief, ...johnhaycigars....at...aol

I may need directions this time. 😞

Dave,

check your mail.

reworking the water system on the farm house now. went with the rheem 53 using propane. pretty simple actually and i am using the outside model which does not require additional venting. good water is probably essential to reduce scaling and efficiency drop. requires a 3/4" gas supply, i will run the line and let the gas co make the connections. positioned the unit right at the distribution header outside the bathrooms wall and drastically reduced the discharge right to the faucets. qualifies for tax rebate also.

JHC, I have electric hot water tank too. Here's my procedure but yours may vary depending on your system.

Step 1: pop the circuit breaker (or unscrew the fuse(s)) for the tank.

Step 2: Close the supply water line to the tank. There should be two pipes coming/entering the tank on the top. One is supply to the tank (cold water) the other is supply to the house from the tank (hot water). To tell the difference, the hot water from the tank to the house is usually insulated. If not, touch both pipes, the warm one is the hot water supply to the house.

Step 3: Screw a garden hose to the drain valve at the bottom of the tank. The drain looks like a faucet similar to your outdoor faucet. Run the garden hose outside. Hopefully the hot water tank is higher in grade than where you are trying to drain it (water runs downhill) If you have to go UP in grade rather than DOWN for the hose, then you might need a pump.

Step 3: Open valve (faucet) on the bottom of the tank and let the tank drain. Open the relief valve on the overflow pipe on the side of the tank (to open it, the lever valve should be pointed straight out) to vent it. Put a bucket under the relief valve/overflow pipe (you'll need this later.)

Also, open a hot water faucet or two in the house (kitchen and/or bathroom). As the water runs out of the tank, it needs air to backfill otherwise it won't drain well.

Step 4: Light up a nice cigar and let the tank drain. Once it's drained, close the drain faucet and open the supply (cold water) valve to back fill the tank a bit.

Repeat steps 3 and 4 a couple of times while still smoking a nice cigar.

Step 5: Once drained and flushed, close the drain valve on the tank. Close the faucets upstairs and open the water supply to the hot water tank.

Let it fill until you see water coming out of the overfill/relief valve. At this time, close the relief valve.

Step 6: Run the hot water in the house at the faucets that you opened during draining. They will spit and cough as the air purges out of the lines.

Step 7: Once the hot water tank is filled again, turn on the circuit breaker or screw the fuses back in to kick the heaters back on.