[joylove]

Hi all, I'm thinking about swapping over to an instant water heater. The house is a 3 bed 2 bath located in CA. The water feed is 1" and the pressure I would say is high; anecdotally.

Currently I have a 30A 208V supply to my existing tank heater.

My main breaker is at 150A. The cable to the sub panel is 2/0 AL.

The sum of all breakers in the 200A sub panel is 245A.

It seems the house was built this wires to the water heater will be replaced as the sub panel is close.

Can I upgrade to an instant water heater?

 

[gregzoll]

It helps to know where you are located on this planet.

 

[Jump-start]

Not enough info. You first need to know what size thankless (kw) you will be installing. Adding the breakers up means nothing, only an NEC load calc determine if your current service is sufficient. Good idea to alert the power company if a load that size eventually gets installed.

On a side note, my honest opinion being if you do not run out of hot water or plan some solar hot water setup latter, keep the tank heater you have now. Tankless heaters arent always worth it. Ive known of people who went tankless and their bills actually went up.

 

[Jump-start]

It helps to know where you are located on this planet.

OP said CA which I would assume means California.

 

[joylove]

Jump-start is right, CA is a code for California.

@Jump-start, I don't have AC but I do have electric heating. So not too much reactive load.

The motivation to go to tankless is twofold; minor space saving but also energy saving. The 2008 water heater I have can go from say 55-60C to cool/cold in 24h.

 

[gregzoll]

CA stands for either California or Canada. You are stating that you have 3 phase power in the first post. Now you are stating the temperature in Celsius, which comes to 131-141 degrees Farenheit.

Your incoming voltage is two legs of 120 vAC at a 180 deg Sine difference.

The Circuit breakers are meaningless. You need to do a Load Calc, which every electric utility has on their website.

Regardless of what you have in the house sitting idle. The Load Calc shows you what the max load would be, if you turned everything on at the same time.

Most OnDemands for 3 Bedrooms, are going to use a high demand of electricity to operate. The payback you will never see in your lifetime.

See the following. http://energy.gov/energysaver/sizing-new-water-heater

 

[Jump-start]

Jump-start is right, CA is a code for California.

@Jump-start, I don't have AC but I do have electric heating. So not too much reactive load.

The motivation to go to tankless is twofold; minor space saving but also energy saving. The 2008 water heater I have can go from say 55-60C to cool/cold in 24h.

Restive would matter as much as reactive. Both pull amps to do their job. In this case a load calc is needed, because the amount of electric heat already place will determine how much you have left over for an electric water heater.

What is your coldest water temperature coming in? Do you ever run out of hot water? In some cases the unlimited hot water can be a double edge sword in that if you never run out you end up using more.

 

[Jump-start]

CA stands for either California or Canada. You are stating that you have 3 phase power in the first post.

208 does not automatically mean a 3 phase service. Their are many homes fed from underground 120/208 networks receiving 2 hots and a neutral. I will let the OP clarify.

Now you are stating the temperature in Celsius, which comes to 131-141 degrees Farenheit.

And? Both or recognized units of measurement.

Your incoming voltage is two legs of 120 vAC at a 180 deg Sine difference.

Only if split phase, see above.

The Circuit breakers are meaningless. You need to do a Load Calc, which every electric utility has on their website.

Load calcs are done per NEC, not the POCO.

Regardless of what you have in the house sitting idle. The Load Calc shows you what the max load would be, if you turned everything on at the same time.

Its based more on probable demand rather then everything on at one. A load calc is not simply adding the nameplates of every device in a building.

Most OnDemands for 3 Bedrooms, are going to use a high demand of electricity to operate. The payback you will never see in your lifetime.

See the following. http://energy.gov/energysaver/sizing-new-water-heater

I agree. Personally, Id stick with a standard water heater. If energy saving are a concern a heat pump model is a good idea:

http://www.rheem.com/products/water_heating/tank/hybrid

http://www.geappliances.com/ge/heat-pump-hot-water-heater.htm
http://energy.gov/energysaver/sizing-new-water-heater

 

[Cement_Frank]

....Most OnDemands for 3 Bedrooms, are going to use a high demand of electricity to operate. The payback you will never see in your lifetime.

They might have a higher amperage draw, but it is for a shorter duration.

So tell me, what will cost more to run assuming 10c/kWH.

• A 30a 240v load running for 30 minutes.
• A 60a 240v load running for 15 minutes.

Its a resistive load, there is no inrush like a motor, we are not pumping water. I fail to see how it is cheaper to heat water slower, and keep it heated.

 

[Oso954]

The electric tankless units draw way more power than a tank type. The larger the difference in desired temp, the less flow you get, so you need to go big to get a decent flow at the desired temp.

It is not uncommon for the large units to be fed by three 40 amp circuits. Compare that to a typical 30 amp circuit on a tank type.

Regardless of any money savings in the long run, you have to be able to support that peak draw.

A lot of homes just can not do it without a service upgrade.

I would recommend that the OP look at a gas tankless, assuming he has gas. Otherwise, I would put a little more money into a new tank type with better insulation than what he has.

 

[joylove]

208 does not automatically mean a 3 phase service. Their are many homes fed from underground 120/208 networks receiving 2 hots and a neutral. I will let the OP clarify.

2 hots 1 phase. ~208V RMS measured with a meter.

And? Both or recognized units of measurement.

The C raise was the units used on the online stuff I found when I googled for tank-size calculators before asking.

I agree. Personally, Id stick with a standard water heater. If energy saving are a concern a heat pump model is a good idea:

http://www.rheem.com/products/water_heating/tank/hybrid

http://www.geappliances.com/ge/heat-pump-hot-water-heater.htm
http://energy.gov/energysaver/sizing-new-water-heater

Thanks, I think I'll stay with what I have.

As suggested by others I'm not overly concerned about shaving dollars by buying an $800 heater; it was more the "if I'm making changes; what's the right thing to do".

@ Cement_Frank The heater basically went cold when it was left off for a day,even thought it's reasonably new and feels cold to the touch. It's leaking heat. I'll put a good jacket on it.

 

[Jump-start]

As suggested by others I'm not overly concerned about shaving dollars by buying an $800 heater; it was more the "if I'm making changes; what's the right thing to do".

@ Cement_Frank The heater basically went cold when it was left off for a day,even thought it's reasonably new and feels cold to the touch. It's leaking heat. I'll put a good jacket on it.

You could, if you only use the heater at certain times, install a water heater timer:

https://jet.com/product/detail/51a3...Gh-JALBcAsFfEWQlhVIdDBz4_RqUMV_J4QaAoUc8P8HAQ

http://www.zoro.com/intermatic-electrnic-mech-water-heater-timer-dpst-eh40/i/G0632073/?gclid=Cj0KEQiAnJqzBRCW0rGWnKnckOIBEiQA6qDBagYPYFIpsgJmlOiRmuD_fmMGJXEI6AtE3dV2q6370bYaAoSg8P8HAQ&gclsrc=aw.ds


Blanket is a good idea, easy investment.
http://www.zoro.com/intermatic-elec...MGJXEI6AtE3dV2q6370bYaAoSg8P8HAQ&gclsrc=aw.ds

 

[Jim Port]

Hard to believe that a modern WH went cold so quickly.

 

[beenthere]

Hard to believe that a modern WH went cold so quickly.

Sounds like something wrong with either the lower thermostat, or element.

 

[joylove]

Sounds like something wrong with either the lower thermostat, or element.

Yes, it was off :vs_lol: The contractor shut it off during the day for some work (not sure what time) and by next morning it was fairly cold. IE: Less than 24h easily.

 

[Oso954]

Hard to believe that a modern WH went cold so quickly.

It is not uncommon in Calif ( in older homes, in many areas) to have the cold water come into an uninsulated crawl space and run towards the back of the house before branching into the garage( often uninsulated) where the water heater is. The heated water then runs from the garage back thru the crawl space, to be distributed to the various fixtures. It does not enter conditioned space until it goes up thru the floor.

If it is all uninsulated metal piping, you essentially have a radiator dumping heat heat from the pipe/water in the pipes. Heat flows hot to cold thru the water column even when there is no water flow.

So, it doesn't really surprise me at all that the temperature drop out here might be worse than what you are used to seeing in a colder climate. You guys are careful about insulating pipes from freezing conditions and keeping uninsulated pipes in conditioned spaces. Your water heater is also likely to be within an insulated space.

If the OP really wants to improve the performance of the water heater, he should insulate his pipes (hot and cold), if they are not yet insulated.

 

[joylove]

It is not uncommon in Calif ( in older homes, in many areas) to have the cold water come into an uninsulated crawl space and run towards the back of the house before branching into the garage( often uninsulated) where the water heater is. The heated water then runs from the garage back thru the crawl space, to be distributed to the various fixtures. It does not enter conditioned space until it goes up thru the floor.

If it is all uninsulated metal piping, you essentially have a radiator dumping heat heat from the pipe/water in the pipes. Heat flows hot to cold thru the water column even when there is no water flow.

So, it doesn't really surprise me at all that the temperature drop out here might be worse than what you are used to seeing in a colder climate. You guys are careful about insulating pipes from freezing conditions and keeping uninsulated pipes in conditioned spaces. Your water heater is also likely to be within an insulated space.

If the OP really wants to improve the performance of the water heater, he should insulate his pipes (hot and cold), if they are not yet insulated.

Interesting. Hot is insulated. Cold is not. I can insulate most of the cold fairly easily.

 

[MrElectricianTV]

Hi all, I'm thinking about swapping over to an instant water heater. The house is a 3 bed 2 bath located in CA. The water feed is 1" and the pressure I would say is high; anecdotally.

Currently I have a 30A 208V supply to my existing tank heater.

My main breaker is at 150A. The cable to the sub panel is 2/0 AL.

The sum of all breakers in the 200A sub panel is 245A.

It seems the house was built this wires to the water heater will be replaced as the sub panel is close.

Can I upgrade to an instant water heater?

No. You will need around 125-150 amps to get the water to heat up instantly for a whole house. An instant water heater needs much more energy to heat water on a spontaneous basis. The 30 amp circuit for your tanked heater works because it uses less energy, and as a result make take around an hour to heat the water.

 

[Jump-start]

Sounds like something wrong with either the lower thermostat, or element.

It certainly is possible.

OP, how old is this water heater?

 

[joylove]

It certainly is possible.

OP, how old is this water heater?

It was there when I moved in and is marked 2008 install date. It's electric and there is no gas available to the home.