I was fortunate to have gas hot water during Sandy. Hot showers were nice and it kept family less miserable which helped my sanity. 

Current home has electric hot water. I plan on connecting my generator to my house panel a few hours a day to do basic things.

I know there are many, many variables to play with, but on average how long does it take a HW tank to heat, and how quickly will a HW tank lose it's temperature when not powered? 

I was fortunate to have gas hot water during Sandy. Hot showers were nice and it kept family less miserable which helped my sanity. 

Current home has electric hot water. I plan on connecting my generator to my house panel a few hours a day to do basic things.

I know there are many, many variables to play with, but on average how long does it take a HW tank to heat, and how quickly will a HW tank lose it's temperature when not powered? 

 

An hour or two... depends a lot on the efficiency and size. Usually within an hour or so.

 

For keeping warm, depends on a lot of variables. For instance, my girlfriend had her handyman put a heater in... and he used those steel-braided supply lines to it. Problem is it is a gas heater, and supposed to be hard piped (copper) around the vent. Changed it out a few weeks back when we started redoing the bathroom, so I shut it down along with the water. Two days later, I drained the tank when I redid the piping, and it was still noticeably hot coming out of the hose. Not the same hotness that it reached the tap on full hot, but enough that I grabbed some soap and washed my hands to get pipe dope off of them. That depends on insulation of the heater, as well as the insulation of the room it is in.

 

My parents have a similar setup, as their generator doesn't have enough to run certain things. They can't run the stove, air conditioning, or drier at all. The water heater can run by itself to heat the water, but then turned off when the well kicks on. If that is the route you take, also make sure you have a large enough heater.

58 minutes ago, Screwball said:

My parents have a similar setup, as their generator doesn't have enough to run certain things. They can run the stove, air conditioning, or drier at all. The water heater can run by itself to heat the water, but then turned off when the well kicks on. If that is the route you take, also make sure you have a large enough heater.

 

What is the output of the generator?

Full size 40 gallon HW heater will have a 240 volt 30 amp circuit. Only one element will run at a time so somewhere around 4500-5400 watts when running.  The top element will heat the water to start and the bottom element is for maintaining temperature.  Your generator would need to supply 240 volts at 20 amps minimum.  That will eat up most all output from medium sized portable generators if the could handle it at all. How long will the water stay warm will depend on what the temperature is set for to begin with and what type insulation it has.  Common averaged price WH do not have very good insulation.  The average 40 gallon electric water heater will take an hour to an hour and a half to raise the temperature of the water 60 degrees.  So how hot the water is at that time depends on the temperature of the water coming in.  Most well water is in the mid 50s.

When on a portable generator for backup most homeowners forgo using certain appliances as the electrical and fuel cost outweigh their benefit. If you have hot water baseboard heating, most add a zone and use it for domestic hot water by using a WH built for that purpose.  Not cheap to install but over time cheaper than electric to heat hot water. 

What is the output of the generator?

8.5kW...

Another option is to replace it with a heatpump hotwater heater or they make add-on heatpump units.  They require much less power and would easily run without totally over taxing a generator.  If you are not familiar with them, a heatpump extracts heat from the surrounding air and dumps it into the water.  They probably use 1/3rd to 1/4 the amount of electricity.

when i was living with the ex-wife, we had gas to heat our hot water in the apt. we ran out pretty often. when i was living with an ex-girlfriend after her, we had gas too...which ran out sometimes. at the shop, i used to have a small electric water heater. it sucked balls. it died, and i never replaced it, 'cause to be honest i don't need hot water there. at home now, my oil heater is also my hot water heater. never ran outta hot water.

Perhaps your gas hot water heater was too small.  I can run hot water 24/7 and it never runs out - but I have a 100 gallon hot water heater.

Anyone try the Rinnai tankless hot water system?

I had looked into those years ago when I had my laundromat.  I ended up installing high eff condensing tank heaters as the instant hot water heaters typically are lower efficiency and are a maintenance headache.  Also they are limited to a certain flow rate so if you have lots of hot water users on at once (shower, washing machine, dishwasher) you will tend to run out of hot water with them.

I know people will say hot water tanks waste a lot of energy, but I have not found that to be the case with a good well insulated tank.  My gas bill during the non-heating season typically runs under $20 a month, and that includes about $6 in base charges.  Thus my total energy charge is about $15 a month and that includes hot water, cloths dryer, outside grill and range top.  Thus my 100 gallon tank can't be wasting that much energy.

 

9 hours ago, Screwball said:

 

8.5kW...

 

Thats your generator output.  You are not getting the full 8.5kw at your panel.  Your gen output is limited to 30 amp through the 240v connector. (~7.2kw)  Not saying your gen cant handle 5400w, but you will probably need to turn everything else off, or you'll blow the generator breaker.

Thats your generator output.  You are not getting the full 8.5kw at your panel.  Your gen output is limited to 30 amp through the 240v connector. (~7.2kw)  Not saying your gen cant handle 5400w, but you will probably need to turn everything else off, or you'll blow the generator breaker.

Reread that original post now... funny what a "n't" missing does to a sentence.