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Old 10-31-2008, 02:17 PM   #1
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tank or tankless waterheater?


I live in a region that has the typical Canadian climate, cold and snow in the winter and hot and humid in the summer. I'm altering some space in my house to accomodate a mother-in-law suite and I'm at the point where I need to spec a water heater. The suite will be used by my mother-in-law only during the winter months, then occupied occasionally by guests in the summer. I'm considering using a tankless electric water heater instead of the tank type, but I am concerned as to whether or not I have enough capacity on my breaker panel. I have a sub-panel (supplied with 100 Amps from the main panel) that supplies my garage and will be supplying the suite as well. The loads for the suite and garage are as follows:

1. heat 2 x 2-pole 15s
2. lights and plugs 4 x 1-pole 15s
3. stove 1 x 2-pole 40
4. kitchen plug 1 x 1-pole 20 (GFI)
5. split plugs 1 x 2-pole 15

I'm looking at a 20 kW tankless water heater that specifies a current draw of 80 amps at 240V. I contacted the factory and they said the 80 amps is a peak rating that will last for approximately 30 seconds and then it will reduce but there are no current vs time curves available because there is no "standard" test conditions (and I can appreciate that). The installation calls for 2 x 2-pole 50 amp breakers (one for each stage of the waterheater). My question is, will the 100amps panel support the loads reliably with the tankless water heater? Will mother-in-law be able to take a hot shower on a cold winter day and still have the coffee maker on? Or should I stick with the more traditional 25 gallon hot water heater (which is half the price as well)?

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Old 10-31-2008, 03:06 PM   #2
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tank or tankless waterheater?


i'd go with the 25 gallons.... more room for Zyklon B..... lol

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Old 10-31-2008, 03:29 PM   #3
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tank or tankless waterheater?


The electric ones in Germany click a lot as they try to keep up with demand.
You have to be skillful to avoid cold water when taking a shower.
100' of 1/2" ID pipe holds a gallon so depending on where the heater is you'll get more or less cold water at first (same as with a tank).
The tank ones are on 5 minutes out of every 5 to 7 hours to make up for losses, so I think the payback period on tankless is pretty long.
There are also practical installation problems; look on other forums.
Hot water for a sink or washing machine is one thing, showers are another.
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Old 10-31-2008, 03:38 PM   #4
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tank or tankless waterheater?


sorry about the bad mother-in-law joke, but if she takes long hot showers in the winter, i think i'd go with bigger than a 25 gallon. nothing worse than losing hot water in the middle of a shower...

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Old 11-01-2008, 12:02 AM   #5
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tank or tankless waterheater?


For the whole house tankless waterheater you may run in few issue which you may not catch it but myself I allready done few of them and my result is a So-So event.

Normally anytime I heard a whole house tankless waterheater normally I try to explain to the customer it will end up upsizeing the service from 200 amp to either 320 or 400 Amp service depending on which POCO and the setup it will be and cost wise it will varies a bit.

Senice you live in Canada the rules will be little diffrent than USA verison the connection will be somehow diffrent due you can have one breaker on for tankless waterheater but if the manufacter say need seprated breakers for each bank of element then do follow the instuction carefully.

There are few issue it will be expected to show up

blinking lights when the whole house tankless waterheater cycle.

some POCO may have strict rules about using the tankless WH due some of the transfomer may not take the load.

and you may end up changeing the subpanel or run the new circuit to the main panel { this will determed by load demand caluactions }

Otherwise a 30 gallon { 114L } will work and it will not affect the exsting subpanel and the wattage on the tank heater useally are no higher than 4500 the tops and it can be run on 30 amp circuit pretty easy.

Merci ,Marc
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Old 11-01-2008, 01:36 AM   #6
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tank or tankless waterheater?


The guys on the plumbing board already dinged me on my anti-tankless ranting so I'll try to stick to the facts... but keep in mind they aren't always a big savings. Consumer reports estimated that it will take 20+ years to pay off the additional up front cost of whole-house gas tankless for a lot of people, and refused to even review electrics because they said the performance isn't what most people would consider acceptable.
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Old 11-01-2008, 06:26 AM   #7
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tank or tankless waterheater?


A 20KW tankless can provide just under 2 gallons a minute of 120F if your incoming water temp is 50F.

But, thats the full 20KW.

So your 100 amp panel wouldn't handle the load in the winter.
And if there is a window A/C, it won't handle it in the summer either.

A 30 or 40 gallon tank water heater would work better with your current service.

Keep in mind, you can turn it off when no one is using the suite.
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Old 11-01-2008, 10:16 AM   #8
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tank or tankless waterheater?


Quote:
Originally Posted by Gigs View Post
The guys on the plumbing board already dinged me on my anti-tankless ranting so I'll try to stick to the facts... but keep in mind they aren't always a big savings. Consumer reports estimated that it will take 20+ years to pay off the additional up front cost of whole-house gas tankless for a lot of people, and refused to even review electrics because they said the performance isn't what most people would consider acceptable.
I am not a fan of electric tankless water heaters either.

Disclaimer: I have never installed one and my experience is just in removing electric tankless and installing gas tankless.

Reasons given: Performance sucked. They just couldn't get enough hot water out of it.

After the gas tankless were put in they were much happier.

Keep in mind that a high efficiency electric tanked water heater has efficiency rating of .95 which is about as high as you can go. An electric tankless is .99 so your savings would be 0.04 which is not much.

Granted there is not the storage issue of keeping the water hot when no one is using any hot water but then again you don't have to have a small nuclear plant in the back yard to heat the water when someone takes a shower.

If you do go with a tanked unit then go with a big high efficiency unit which can be set at a lower temperature versus a small unit that will have to be set at a higher temperature to get the water needed for a shower at a reasonable temperature.

A 25 gallon is not an option. I don't know of anyone who can take a nice shower with 25 gallons of hot water. Remember that a tanked water heater will start to get cooler once half the water is used as cold water comes into the tank. A 25 gallon water tank will give you about 6-7 minutes of shower time. Not a good way to keep a mother in law happy.
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Old 11-03-2008, 07:19 AM   #9
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tank or tankless waterheater?


Thanks folks,

You've made my decision much easier, I'm going to go with a 30 gallon tanked waterheater. I wasn't sure what MdangermouseM was talking about at first so I googled it, NICE ONE!! Mother-in-law came to us on Saturday asking if I could install a bench grinder on the granite countertop in my butler's pantry so she could grind glass for her stained glass window class. She then threw a temper tantrum when we said no and stormed upstairs, my 3 year old acts more mature. We need to get her into her own space so she can grind her glass in her own kitchen, at least she'll have enough power to crank up the grinder now that we won't be using it all to heat the water.
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Old 11-03-2008, 07:46 AM   #10
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tank or tankless waterheater?


i was thinking more along the lines of a 50 gallon for the showering...25 or 30 will not last long.
surprised more people did not comment on my little joke.... owell, it WAS pretty bad.....

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Old 11-03-2008, 08:14 AM   #11
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tank or tankless waterheater?


30 gallons will be fine, my wife and I and 3 kids use a 40 gallon gas waterheater. After all I don't want her to be "too comfortable".
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Old 11-03-2008, 08:33 AM   #12
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tank or tankless waterheater?


good point.... 30 should be good for a 15, 20 minute shower. we have a 50 and rarely run out.
and a grinder MOUNTED on your granite top???? "SHOOT HER NOW! SHOOT HER NOW!"

now, back to how to hook up that 220v line to the faucets for her......

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Last edited by DangerMouse; 11-03-2008 at 08:35 AM.
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Old 11-03-2008, 04:15 PM   #13
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tank or tankless waterheater?


Gas water heaters have twince the recovery rate of an electric.

Of course, if she runs out of hot water.
I'm sure she won't mind taking a bath or shower at your house as an excuse to visit you.
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Old 11-03-2008, 08:37 PM   #14
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tank or tankless waterheater?


Quote:
Originally Posted by Canada Mike View Post
Thanks folks,

You've made my decision much easier, I'm going to go with a 30 gallon tanked waterheater. I wasn't sure what MdangermouseM was talking about at first so I googled it, NICE ONE!! Mother-in-law came to us on Saturday asking if I could install a bench grinder on the granite countertop in my butler's pantry so she could grind glass for her stained glass window class. She then threw a temper tantrum when we said no and stormed upstairs, my 3 year old acts more mature. We need to get her into her own space so she can grind her glass in her own kitchen, at least she'll have enough power to crank up the grinder now that we won't be using it all to heat the water.
Hi Mike, I'm in Canada also! I have just gone through an evaluation of tankless water heating! In my case it was using natural gas heating!
The Bosch heater gives a temperature rise of about 70F.
So if the input temperature of the water were 45F (common in a Canadian winter), its output would be only 115F. Certainly not enough for dish washing!
Using a h/w tank is said to be inefficient, due to heat loss from the tank!
But, here in Canada during the winter, this heat helps heat the house. So, its not really lost.
Of course, in the summer, this heat may need to be removed using A/C. So, now the advantage of using a h/w tank is lost.
Its my opinion that you made the correct choice, for our environment!
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Old 11-04-2008, 04:45 AM   #15
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tank or tankless waterheater?


another option could be a water heater 'blanket'......?

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