Tankless job. (pun intended)

Status
Not open for further replies.
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I am about to install a couple of tankless water heaters. Not the kitchen-sink Insta-hot, but the whole-house, no-storage-tank kind, that supposedly meets continuous demand. Of course, anyone could leave a hot faucet open, but...

One was on site, the other one is on the way. The one I saw was rated at 28Kw, divided into four 7Kw (29.2a) feeds. I did a forum search with the word "tankless" and found just enough info to not quite answer my questions, so here goes:

1) Is a tankless water heater considered to be a continuous or non-continuous load? That will make the difference between #10 on 30a breakers and #8 on 40a breakers.

2) To what degree do load calcs apply to existing installations as it does in new work? This new load (116.8a) may require a 200-to-400 (320, actually) service upgrade.

3) The customer wants me to wait to see if he has main-breaker tripping problems before he's forced to commit to a service upgrade. Is that okay to agree to, or must we not even approach the possibility?

All replies appreciated!
 
http://seisco.com/pages/electrical-A-intro.html
This location list it as a non-continuous load and 4 30 amps ckts.
3) The customer wants me to wait to see if he has main-breaker tripping problems before he's forced to commit to a service upgrade. Is that okay to agree to, or must we not even approach the possibility?
Click to expand...
Thats too late. Do a load caculation and see. This web site tells you how to caculate the new load.
 
Last edited:
LarryFine said:
1) Is a tankless water heater considered to be a continuous or non-continuous load? That will make the difference between #10 on 30a breakers and #8 on 40a breakers.
Click to expand...
The nameplate didn't call out any specific OCPD/conductors?

I'd say it's not a continuous load, but I would still consider the 8's as piece of mind.

2) To what degree do load calcs apply to existing installations as it does in new work? This new load (116.8a) may require a 200-to-400 (320, actually) service upgrade.
Click to expand...
I'd say it counts. I tend to think of someone filling a glass of water, and think a service upgrade isn't necessary. But then I think of my wife's showers, the dishwasher's cycle, and the washing machine all in a line, and see the service dripping with sweat.

3) The customer wants me to wait to see if he has main-breaker tripping problems before he's forced to commit to a service upgrade. Is that okay to agree to, or must we not even approach the possibility?
Click to expand...
I'd push for the upgrade. But I am young and foolish. :)

Disclaimer: I imagine you're aware I've never played with these.
 
benaround said:
Bob, That's what I call an answer!!!! Good job.
Click to expand...
Really! He even figured out which brand and model I'm looking at: the Seisco RA-28.

"Vewy impwessive, Mistew Kottew!" ~ Arnold Horschack
 
He will likely be very unhappy with this heater.I installed one few years ago and customer said with its cycling on and off it was making lights flash.We had to unhook 1 of the heaters to slow it down.As to upgrade i think you need to do the load calc. first.
 
ptonsparky said:
I am sure the local utility would appreciate a heads up. This type of load in the typical residential area will be noticed by all.
Click to expand...

Actually the one i installed was in the old part of Tampa and TECO told me its hurting them.The neighborhood was 1920s homes and they just are not prepaired for the remodeling let alone this kind of 28 kw for 30 seconds.I would think anyone shareing the transformer would get flashing too.
 
Last edited:
I put one in my own house a couple of years ago. It was a Seisco 28 kw I got through Costco. The manufacturer sales rep said that it would run 4 showers at once. Installed, it wouldn't keep up with one shower and the lights would dim. I have a newer 200 amp service and very little other load. I amp checked the heater in operation, and it was in limits. I don't think I did a voltage check, though. I wish I would have. The heater went back to Costco, and I put in a tank water heater. There are really good gas tankless water heaters available, some are even made to be installed outside, so you don't lose house space.
 
1. It's not a continuous load.

2. The alternative to performing a load calculation is to take load measurements over a 30 day period, or to look at a year's worth of utility records. The intent of either method is to get the maximum demand over that period. Add 25% to that value, and see if the existing service has room to add the proposed load. My guess is that it will not have the room.

3. The suggestion is absurd, and you should not entertain it for even a moment. My training tell me never (did I say "never"? I meant "never, never") design a system in such a way as to force a protective device to act except in abnormal or emergency situations. You do not rely on a breaker tripping as a means for testing the installation.
 
I think that you should go ahead and calculate the lload on the whole house with the heater included. If it wasn't large enough, I wouldn't install the heater.
That heater will pull it's rated load, every time it comes on.
I personally wouldn't have one in my home.
Can you imagine what would happen if the homeowner isn't home and has a (major) plumbing leak on the hot water system? Or the cat turns the hot water on while getting a drink (it happens).
I wouldn't be suprised if the utility companies start adding a surcharge for powering these type heaters. 28KW on and off for a few minutes at a time has got to cause them problems. Just imagine if everyone had one of these, the existing POCO system couldn't handle the load.
Just my opinion.
steve
 
UPDATE:

The customer has decided to return the tankless water heater and stick with their storage heater. Mixed blessing, I guess.

A half-hour drive each way down the drain. I told you this was a tankless job! :)
 
Well this is just my 2 cents.

If I were to use a tankless hot water heater, I would get a gas one. Just from the installation standpoint, you would spend far less on the infrastructure with the gas version, b/c with the gas one you just need a 15/20A 120v circuit for the fan and control circuitry and the gas service that would be easy and relatvely inexpensive (at least compared to the copper needed for the electric version) for a plumber to connect. That being said, a gas service line can much more easily support the high, but intermittent energy demand (ie 100k+ BTU, when active) whereas an electric service needs to be so oversized in comparison to the remainder of the house's total load that you're possibly doubling the size of your service just for a water heater.

The electric version just seems to be a poor design choice under just about every circumstance I can imagine. And while I realize that this is an NEC forum, but there are just some times/circumstances where gas is a better choice.
 
I guess that this is just a comment for future reference:

The gas versions of these tankless heaters have a minimum flow requirement. If you are trying to run your hot water slowly, then the heater will cycle cold.

We installed a gas tankless heater for a new bathroom. I like to take very long showers, but for most of the duration I like to turn the flow down low, just enough to stay warm. It was quite a shock the first time I adjusted the flow rate in the shower to the minimum setting, only to have the water suddenly drop to Boston winter supply temperatures.

I've seen people suggesting using a tankless heater to feed into a small storage heater; for low flow rates the storage heater provides the hot water, for higher flow rates the tankless heater provides the hot water.

I've since moved, and in the new digs there has been some thought given to installing an electric tankless. I'll be keeping this thread in mind should the discussion ever come up again.

-Jon
 
The bottom-line concern I have here is that the distributor of these heaters in my area seems interested in developing a work relationship with me (they sell, I install), but if a portion of their customers continuously return the heaters, they won't like me very long. "Why do I need a service upgrade to install an "energy-saving" appliance???"

One of their other customers told me the company give the inpression that installing this equipment is almost a do-it-yourself job, and they are suprised when they hear the price I give them (which also includes the plumbing work). They even received a $300 quote from another electrician (who never came back to do the install; gee, what a mystery.)
 
LarryFine said:
The bottom-line concern I have here is that the distributor of these heaters in my area seems interested in developing a work relationship with me (they sell, I install), but if a portion of their customers continuously return the heaters, they won't like me very long. "Why do I need a service upgrade to install an "energy-saving" appliance???"

One of their other customers told me the company give the inpression that installing this equipment is almost a do-it-yourself job, and they are suprised when they hear the price I give them (which also includes the plumbing work). They even received a $300 quote from another electrician (who never came back to do the install; gee, what a mystery.)
Click to expand...

Well the "Energy Savings" are only realized when you are not using any hot water. The point is that you are not heating water when you're not using it. The biggest difference in the power utilization between a standard hot water heater and an on-demand version is that standard one transfers enough energy to the water in the form of heat over a protracted period of time. The on-demand unit has to transfer the same amount of heat to the water, just over a much shorter period of time, and this requires a much larger supply. The service upgrade is just to have the electrical capacity to supply that same on-demand water heater when it is being used. And although I see the utilization of this type of equipment as having a short duration with the distintct possibility of continuous operation. It is that possibility of continuous or extended utilization for which you would need to calculate your service needs. This is where you end up needing to increase your service entrance for a single piece of equipment.
 
charlie b said:
My training tell me never (did I say "never"? I meant "never, never") design a system in such a way as to force a protective device to act except in abnormal or emergency situations.
Click to expand...

I take it you only provide one receptacle per circuit? ;)

Just curious.
 
A plumber friend of mine has one at his summer house on cape cod. He's very happy with it. I'm not sure of the brand. If I did a load calc. I'm betting the service would be inadequate. It has 3, 50 amp circuits. I don't remember the exact KW rating. The reality is he's never had a problem. The elements cycle on as needed based on water volume, and his one shower probably only cycles u to two of the elements. Charlie's method of demand monitoring might prove the service adequate.
 
I have installed some 60 amp units in homes and in some doctor offices and it was hit or miss as far as them actually working. I would not even consider it on less than a 200 amp service with a existing load no greater than 110 amps. I personally like them in commercial applications but not crazy about them for residential applications.
 
I was seriously thinking of installing a Seisco tankless water heater in my own home in the very near future because my 50 gal electric tank heater is on its last legs.But after reading some of the posts I am now not so sure.I do have a 200amp SQ D main panel and I would have to install a sub panel if I decide to do this but is it really worth it?Would I save that much over the years?Does anyone here really know how well that they perform and are they basicaly trouble free units?Then there is the added cost of the sub panel and not to mention the cost of the 45 ft of feeder cable.I just don't know if it's really worth it.What do you guys think?
Rick
 
Status
Not open for further replies.
Top