Water Heater Install Question

[Craig Robison]

I have a perfectly good 40 gallon Natural Gas water heater (in the attic) it sometimes proved to be insufficient with company in town so I did what you should not do and cranked up the temp to about 145-150 and it seemed to help although we still ran out during times of heavy use. Now we have a kid on the way, water is SCALDING HOT and we are going to need more of it anyway. Long story short I found that it was cheaper to add a second 40 gallon water heater (plenty of room) than to replace the existing one (I hated the idea of removing a good water heater, it is only 5 years old). Also, I went electric instead of gas, mostly because I did not want to cut a hole in the roof for the vent AND the electric model was cheaper AND I just happened to have a no-longer-used 10 gauge wire running right to it. Natural gas prices are sky-rocketing but I still think that a gas water heater is cheaper to operate than an electric model SO, I plumbed them in series rather than parallel. That is to say the hot water leaves the gas water heater and goes into the electric water heater then into the house. In this manner I figure that the gas heater is still doing most of the heating and the electric one is more like a storage tank. I have set them both to 125 degrees, the minimum temperature that the dishwasher manual recommends (to do this I filled a bucket full from the T&P valve and took the temp right there). My question, is there anything wrong with having the water flow from one to the other in this manner? I cannot see why the electric water heater cares what temperature the inlet water is. For what it is worth the guy at Home Depot thought it was brilliant, but he aint a plumber, and neither am I... Any Thoughts?

Craig

[Tony Hwang]

Hi, I always had two gas heater in series. But have no experience with gas-electric combo. I'd think they'll have different recovery rate. Tony

[Craig Robison]

I agree, I suspect that the 3800 watt, single element, el-cheapo electric water heater recovers pretty slow. Compared to the 30K BTU NG heater... another reason I put them in series. Craig

[buffalobill]

you will next wind up with a 75 gallon tank if you can get it thru your doorways like ours we run at 150F, oops you're in the attic. recheck your 40 gallon gas hot water tank for replacement of the DIP TUBE if you have rapid temperature drop on the output of your gas hot water tank. i would use a drain pan and drain pipe under each tank with a battery water alarm [$10 home depot] in each pan.

see also for dip tube and other repairs:

[buffalobill]

Energy-Efficient Water Heating

[Bob]

The only time you should pipe two water heaters in parallel, is when they are exactly the same capacity and flow rate. I think you'll find that the electric water heater is going to cost you a lot more to operate. I also think that if you turn off the gas supply to the gas water heater, you're going to be running out of hot water. Water heaters are rated by their 'recovery rate', or how fast they can raise the temperature of the water. This is typically a rise of 90 degrees. The recovery rate of an electric water heater depends on the wattage of the heating elements. A typical electric water heater with two 4500-watt heating elements takes about two hours to heat 40 gallons of water. A typical 40 gallon gas water heater takes about one hour to heat 41 gallons of water.

[Joseph Meehan]

You did hook it up the right way. I might have put the temp of the gas a little higher than the electric to avoid having the electric kick in under normal conditions. Putting then in parallel would have been wrong.

I suggest that when the time comes that you are ready to address this problem, that you consider a more conventional solution. In the long run a single larger high recovery heater is going to cost you less and require less maintenance than your current setup.

[trader4]

" You did hook it up the right way. I might have put the temp of the gas a little higher than the electric to avoid having the electric kick in under normal conditions. Putting then in parallel would have been wrong.

I suggest that when the time comes that you are ready to address this problem, that you consider a more conventional solution. In the long run a single larger high recovery heater is going to cost you less and require less maintenance than your current setup.

-- Joseph Meehan "

I second that advice. Two seperate small water heaters are going to have considerably more heat loss that one larger unit, leading to higher operating costs. How much did you manage to save by going with a second smaller unit, instead of just buying a bigger one and selling the old one? You'd be surprised what you can sell on Ebay!

Also, I'd measure the 125 degree temp at the point of delivery to the dishwasher and set the heater temp based on that, not right at the heater.

[Bob]

I third that advice. In addition, when cold water enters a water heater, humidity in the air can condense on the outside of the tank, and cause it to rust. Water heaters that are too small for the household's needs, will have to be refilled more frequently, and this can cause excessive condensation.

[scott21230]

I would have put in an on demand whole house hot water heater.

[hallerb]

He did a GOOD THING!

If capacity is still a issue up the temp of the gas tank back to 150 degrees, then install a tempering valve:)

Set the valve to 125 or whatever you want. It limits the maximum temperature going out to faucets to what its set at. So no one can get scalded.

I nearly installed a tempering valve on my old tank, I was going to take the dishwashewr water before the valve so dishwasher would get 150 degree water, and everything else 125....

About that time my tank failed so I went with a 60 gallon pro high BTU tank. That fixed our capacity issues, but cost a fortune and only had a

6 year warranty

Sadly standby losses with 2 tanks will DOUBLE, If I were you I would add lots of insulation to both!

[Bob]

On the bright side, the last time I asked Bradford White, a 6 year and 10 year warranty were made exactly the same. The increased price difference just reflects the money it costs BW for the extra 4 year replacements. The only time it pays, is if your water heater breaks within that 4 year period.

[Joseph Meehan]

That will increase energy use and decrease the life of the heater.

[Bob]

[Craig Robison]

The electric water heater was $179. A 60 Gallon gas heater was over $400. So I figure I saved at least $220. As far as eBay goes, I looked, I MIGHT have grabbed $50-$75 for the old one. The question then is how long will it take me to run $220 of electricity through the electric water heater? I'm guessing a while, and, a 60 Gallon gas heater would have had an increased operating cost over the 40 gallon I have now. I suppose if you really wanted to crunch some numbers you might come up with the most cost effective long-run solution. Next thought; Would going from 40 to 60 and then dropping the temp from 150 to 125 really have increased my capacity that much? It would be 20 more gallons at a lower temp? Again I suppose you would have to run some numbers..

Craig

[Joseph Meehan]

I considered that. Since I don't know the cost per therm of each source I stuck with energy use not cost. You are right however and that should be considered as well. I hinted at that with my initial comment "I might have put the temp of the gas a little higher than the electric to avoid having the electric kick in under normal conditions."

[Joseph Meehan]

Craig Robison wrote: ...

That would depend on your local cost structure. I would guess that in some situations you would recover the investment cost quicker than you think. In others it might not be worth it.

You also need to consider the recovery rate. Not all water heaters can re-heat water at the same speed. A high recovery 40 may be enough if your current model does not have a high recovery rate. I would also add that having one 60 gallon heater will result in far less standby losses than two

40's.

[trader4]

" Would going from 40 to 60 and then dropping the temp from 150 to 125

I did run some numbers. Assuming the incoming cold water is 50 degrees, mixing 150 with it 3:1 gives you the 125 temp. So, a 40 gallon tank of 150 water could be mixed with 13.3 gallons of 50 degree water to yield 53.3 gallons of 125 water.

So, going to the 60 gives you 60 gallons at 125, vs 53.3 by the mixing approach. The other factor to consider is the heat loss through the tank is also proportional to the temp difference. Assuming an ambient of 55 degrees, with water at 125, you have a delta of 70 deg. At 150, the delta is now 95, an increase of 36%. So, your gonna lose 35% more energy through the tank with the higher temp. I think these two together mean that unless there is some other issue, like space, the bigger tank is going to be the better solution.

[hallerb]

1. [e-mail]

I priced them today at Lowes.

The warranty is 10 years, and the price for the larger unit a $1000.00

This is like buying a hybrid car to save $ on gas.

The payback period is forever since the purchase price for both the on demand tank, and hybrid car is way too much.

[Bob]