I have a customer requesting a price to hook up a tankless water heater. I know a service upgrade would be involved so I told him to get me the specs on the unit before I submitted a bid.

He called back and said the unit is 28.5 KW ! At first I thought he was mistaken on the load but after doing some searching I found that they actually draw that much for a whole house unit.

My question is, I don't see where the code actually adresses this type of unit, so what is the normal way to figure this into your service feeder calc ?

I see if I use the optional method I can put it in as the water heater load but would hardly make sense since it is almost 3 times larger than the central heat of the next step in 220.82 (c)

Any ideas or suggestions from people who have installed these would really help

Rich, my first suggestion is to make it clear in your proposal that you are not responsible for lights dimming whenever somebody turns on a hot water faucet. Second suggestion means less revenue for you, but a good possible alternative. They also make gas powered tankless water heaters. They still sometimes need a 120 volt outlet installed for controls, so you can still make some dough on it, depending on the make and model.

28.5 KW???! Holy moley, that's (28,500/240) 118.75 amps! Add in the required 125% overhead, and that means a (118.75*1.25=148.4375) 150-amp circuit.

I'd want a separate service for a single load like that.

"Are you sure about those five minutes?!" - My Cousin Vinny

Thanks for the reply's, I'm thinking of leaving the existing 150 amp main panel alone and then upgrade the existing meter to 300 amp and then feed a separate 125 amp main panel just for the heater.

I doubt he will want it done after he sees the cost, I just don't understand why they would make these things so big unless they think every house just has a spare 125 amps to play with.

Here is a link to a similar unit that is 22kw
http://www.tankless-water-heater.com/products.html

We've seen a few of these and I really don't understand why someone would want one. I know they only run when hot water is needed, but they draw so much more than a standard water heater when in use, I doubt there is an energy savings. One of our customers put in one of these with a recirc pump, so it runs constantly. The same customer had us install a steam generator that draws 126 amp constantly when in use. He was surprised when I told him he had to have a service upgrade.

One of our customers put in one of these with a recirc pump, so it runs constantly.

Betcha it doesn't last very long. I believe they have a duty cycle or at least are designed for intermittent duty. Also, a recirc pump pretty much goes against what the heater was designed for, that being on-demand water heating. If it's going to maintain hot water there are other much less expensive alternatives such as a conventional water heater.

-Hal

we installed one of these tho not quite as large. Step one was a service upgrade. The unit we installed came with a panel with the unit. Fed 125A to the panel and it had 3 50A two poles. The controller put power where it was needed in the unit. It had 6 heating elements and demand dictated how much power/how many elements were used. Interesting set up. Rod

Oh boy... something like that in the US... here in Europe those beasts are wired across the three phases and still require a 3x35A 400V feed (that's a standard service for a single family building here...)
They only have one single advantage... they provide instant hot water where no gas is available. That's the only reason they were invented.

Tankless gas water heaters have been de facto standard here for ages. Apartments built around 1900 and later (the big majority of Vienna's houses) didn't have hot water originally, or if they did it was already tankless gas water heaters. They were invented in 1885 I think. Over the years functionality to add hot water central heating to small wall-mount combi units was added (caught on around the 1970ies). Nowadays you can see such a tankless water heater/central heating combi boiler in almost every renovated apartment and smaller single family home (those combi units serve a floor area of roughly 2000 square feet for heating).

It's not a good joke, but I have to add it... in Austria electric tankless heaters are basically unknown, whereas in Germany they seem to be quite popular. And each time somebody shows up at a German board asking: "What line do I ned for a 28kW tankless?" I say: "3/4" iron pipe!"

"Great melting service cables, Batman!"

I thought the 9.5kW units we have over here pulled a lot of current. They've become more common in recent years, often fitted to supply hot water in a location remote from the main tank, for example:

Triton 9.5kW Water heater

One thing you need to remember with these units is that the output temperature is inversely related to the flow rate. In the U.K. one above, for example, to get water out at 140 degrees you'd be looking at only about 3/4 gal. per minute flow rate based on our average water supply temperature.

According to the specs on that 22kW American unit linked to above, you could get only just over 1-1/2 gals. per minute for 140 degrees out with water going in at 50 deg.



[This message has been edited by pauluk (edited 09-03-2005).]

Obviously, a storage cylinder or tank is the best option, for several reasons, if you have room for it.
1. The maximum current drawn is much less, leading to cheaper wiring and switching.
2. Flow rates are only dependant on the faucet size and pipe bore/pressure, 1.1/2 US gallons a minute @ 22kw is hopeless for running a bath.
3. Off-peak supply or heat-pump technogy can be used to reduce poco bills, dry the damp basement, ( or chill your wine store!)

We have a 15psi presurised 230v, 2.4kw x 200 litre (52 US Gallon) chauffe-eau, running off-peak, size 5ft high x 18" diameter, producing domestic HW at 60C (140F) which we find adequate. It's so well insulated it holds hot water for a week when turned off. Our Wash m/c and dishwasher take in cold water, and run at night on off-peak, with intergral heaters, using time-clocks plugged into the recepts..
Currently I'm researching a heat-pump chauffe eau for the renovation, but the cost is off-putting, it looks like they're about US $2500-3,000 here, with the dreaded 19.6% sales tax on top(!), which puts the capital payback to beyond the time when we'll both be drooling in a home for distressed gentlefolk! Anyone know of a reliable cheaper US model for export?

Alan





[This message has been edited by Alan Belson (edited 09-03-2005).]

The cheapest way to heat water around here is to scavenge waste heat from the AC compressor. That gives you free hot water and your AC runs better.

When it comes to hot water, I say "tanks a lot."

Although a trend is developing which will have us saying "Tanks for the memories."

Tank you all for listening.

... What's all this I keep hearing about thankless water heaters?? Putting myself in it's place as just a "water heater and an inanimate object",as most people refer to them,I believe that it's not the water heater thats thankless,but the penny-pinching home-owner who doesn't want to part with their hard earned 'scarole to have this poor, abused,denizen of the cellar installed by somebody showing much too much cleavage in the "steerage deck" if ya know what I'm sayin'...Do you guys out there think that it's actually easy being a hot water heater??? The constant pressure,the heat and humidity,the lousy lodging accomodations,... Yeah,maybe it's a thankless job,but someone's gotta do it right?? I'd be a might bit thankless too if'n I were subjected to those conditions day in and day out... That's it,my rant is over...so the next time you guys wanna pick on something,by calling it "thankless" try pitching it to something that deserves it,..like waffle irons,...now those darn things are thankless...
The following was a public service message by: a subsidiary of:


Russ



[This message has been edited by Attic Rat (edited 09-03-2005).]

Russ:

You've done it again!!

My downstairs neighbor's gonna think a lunatic lives above, as I'm again ROFL from your post! (Well....maybe it's true...)

"Tanks a lot!!"

Tony

Very good point, I work in very large super markets and any heat that can be scavenged from the refrigeration equipment is used to heat the building and water. This saves money directly by using less fuel to heat and by shortening the run time of the condenser fans.

How is this accomplished with dwelling unit ACs and water heaters?

An AC unit is a heat pump. When used to cool a home in summer, heat is pumped out of the house to the exterior unit, whether this is a window or a split-unit design. A simple heat exchanger/circulator, (a desuperheater) can be inserted in the AC refrigerant lines to remove some of this heat and transfer it to a water storage tank at 60C / 140F. The heat extracted is essentially 'free', the running costs are simply those involved in capital, fluid circulation and control.
Actually, fitting such a device will reduce the cost of running the AC unit and prolong its life. There are some reservations:
1. The Heat Exchanger has to address the danger of refigerant gasses getting into the potable water supply, and must be sized correctly.
2. The device will be non-operational when the AC is off or reversed, (ie winter), so an alternative hot water heater is needed.
3. Cutting into the refrigerant lines might pose warranty problems and also requires a HVAC engineer to re-gas the AC unit. http://www.doucetteindustries.com
shows a typical unit and a savings chart. Go to: products: desuperheaters.
I'm still looking; I want a stand-alone air-water unit at a reasonable cost, which I can park in the boiler-room to extract heat lost by the boiler in winter or gained by solar effects in summer.

Alan





[This message has been edited by Alan Belson (edited 09-04-2005).]

Alan
Check this site out for cold air heat pumps. Not sure if its what you are looking for or not. The manufacturer is local to me in Maine http://www.nyletherm.com/spaceheating.htm

Walrus,
That is EXACTLY what I've been looking for! I e-mailed them this evening, so hopefully we can get down to the Customs and Excise/shipping nitty-gritty!
Thankyou.

Alan