On Apr 7, 10:24 am, "Thomas G. Marshall"
. com wrote:
Ok, our 40 gal gas water heater is failing. About 10 years old, which I
hear is ok.

But every time I talk to someone about their 40 gal water heater, they all
complain that they run out of hot water (comparable size homes and kids).

Bur our builder (and all builder's we spoke to when looking to build)
*insist* that 40 gallons is enough.

But we were always worried about running the wash or dishwasher before
showering, or two long showers would result in the 2nd losing water.
Complete with those water saving disks etc.

1. Is 80 gallons overkill? Perhaps I'm reacting viscerally.

2. Am I going to notice a large gas usage increase?

3. Are there rules in place limiting the water tank sizes?

4. Are there any particular brands to look for or stay away from?

I'm sorry for the barrage of questions.

My comments to others coments.

40 gallons enough? Items that affect hot water usage and volume
1. Is there a dip tube.
2. Is the hot and cold pipes connected properly
3. Baths instead of showers
4. This depends on the life style of the occupants
a. Length of showers
b. Is hot water running while brushing teeth
5. Number of occupants
6. Hot or warm laundry
7. Recovery rate of the water heater
8. Are the shower heads 1.6 gpm or 2.5 gpm or much higher
9. The distance of piping between the water heater and the usage
points
10. Are the pipes fully insulated
11. The temperature of the water heater
12. Amount of sediment in the tank


Any time the occupants presently run out of hot water and a new system
in installed and there is plenty of hot water the amount of gallons
will then go up. As for the increase of cost, this depends on the
amount of increase of hot water in gallons and the efficiency increase
of the new unit.

Tankless water heaters:
Generally the only information on efficiency is verbal from the
salesperson. The efficiency of water heaters is in AFUE and most
tankless units are not rated in this manner. I agree there is no
standing loss due to the lack of a tank. The efficiency on large
usages can be ok the efficiency on the small usages can be very poor.
This would only make it a fair choice.

There are only a few that are above 90% or what we call condensing
units. The units that are designed to keep a constant output
temperature are expensive and complicated. And hope no repairs are
needed. If the water in your area is full of sediments they need
regular cleaning. They should have a sediment filter to keep
particles from clogging their filter. If one wants a on-demand
circulating pump they will not work with tankless units. They have a
minimal flow rate to turn on.

Contrary to belief they do not get water to the faucet faster,
actually a small amount longer. On has the added wait of the burner
to ignite and warm up the heat exchanger.

They are expensive for the good ones. They normally need a larger gas
line and in some homes this is real expensive to install. The
stainless vent pipe is expensive.

And to think I used to recommend these units.

I would recommend looking at a unit such as a Phoenix ( there are
other companies). This type of unit is 90%+ AFUE. They have a high
recovery rate. They do require a large gas line and are expensive.
The up side is they can reduce the cost of heating water about
30-40%. In most parts of the world where the heating load is not to
big they can also heat the home.

The older style of tankless I used to have would shut off on the low
pressure of our water pump, ever take a shower from Michigan well
water in the winter? I would hope the newer units are better.

Q: What happens when half a tank is used up? Does ice cold water rush
in and
cool everything down? Is it thus better to gang two together somehow
to
have the 2nd take over when the first is refilling?
A: Ice water will not rush in. The way the two tanks in series works
is. The cold water is plumbed into the cold inlet of the first water
heater. The hot outlet from the first water heater is plumbed into
the cold of the second water heater. The hot outlet of the second goes
to the hot water to the house. When the faucet is turned on the cold
water immediately starts flowing into the first tank and hot water
from the first tank goes to the second tank. As the first tank cools
down the burner (assuming gas) turns on and heats the water in the
first tank. If the rate of water used is higher than the first tank
can heat then cooler water enters the second tank. The burner of the
second tank will turn on once nit is cooled past its set point. If
enough water is run at a rate high enough then the outlet temperature
will decrease from the second tank

Q: Cold water sinks so it pushes the hot water up, although you will
get some
"warm" water before cold as the hot water runs out.

A: Cold water will sink but... In a water heater there is a dip tube
and water is directed to the bottom of the tank when entering.

Q: They say tankless is 80% more efficient than an electric tank.
That one is more expensive, but it recoupes in cost in two to three
years.

A; are we comparing electric to gas? If not and your are going to put
a tankless electric water heater in that will supply enough flow
rate... wait till you get a price on a electric service and wiring to
handle this type of unit (OUCH).

Q: Spare us the tankless marketing bullship. Standard water heaters
DO
NOT run constantly. They are well insulated and have a large thermal
mass of water inside.

A: I would question well insulated. The temperature difference is
greater from the inside of a water heater to the space it is installed
in. We put R-30, 38, 50 in our attics and maybe R-15-20 in water
heaters. Has anyone ever looked at the vent pipe temperature when the
unit is not running (nice and warm). Or the temperature of the hot
and cold pipe when no water is being used. And guess what there is
almost nothing that meets code we can insulate the most important two
pieces of pipes in the DHW system. Code requires 3 inches minimal for
combustible for standard vent and fiberglass and foam will not meet
this requirement.

The amount of thermal mass has nothing to do with the loss from the
tank. Heat loss by conduction is Q=U * A * Delta T * H (Q is the
amount of BTU's, U = 1/R-value, A = Area, Delta T= temperature
difference, H = hours). Heat loss by radiation is determined by the
surface temperature, texture and emissivity. Convection, is based on
the surcace temperature, the temperature of the air around the tank
and the amount of the insulating value of the air film against the
tank.

Q: Oil fired tankless is the way to go. All the hot water you want,
never
run out and it stops running just as soon as you cut off the faucet.
I know because I had one.

A: I do not know the cost of gas vs. oil in your area. Assuming oil
at $3.00 per gallon and gas at $2.00 per therm (100,000btu) and both
units at 90% AFUE. The cost per million BTU's for oil is $31.97 and
for gas $22.22. I would think gas is less than $2.00 per therm, I've
never seen it that high, Oil (anyone know how much per gallon). And
Oil is unlikely 90% efficient.

What kind of oil unit do you have that shuts off when the faucet is
shut off, sounds like a tankless unit, I was not aware of such type of
unit.

Q: and the tankless boys can stick them. I like HOT water. Not
lukewarm
water.
A: A properly sized tankless water heater can give you scalding
water.

I try to deal in facts
AndyEnergy
Residential energy consultant