Need advice determine if I can use a electric tankless water heater

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Old 08-12-19, 04:40 PM
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Need advice determine if I can use a electric tankless water heater

I am remodeling a 960 sq ft home. The home is all electric with only one bath. the current tank water heater is located in the tiny bathroom. In order to fee up floor space, I want to remove the tank water heater and replace with a tankless one. The main amp in the electrical panel is 200 amps. I would like additional ice on what type and size of tankless I would need. The house is on pier and beam. Iím not sure how to calculate the loads of all the equipment to make sure I do not purchase the wrong size heater. I have read the specs on various brands and models and some indicate heat amp load and whole house amp. Iíve done lots of research and donít want to spend thousands on electrical upgrade but really need the extra sq ft in the bathroom. Thanks for any advice you can give😰
 
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08-13-19, 04:42 AM
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Look at the charts for the tankless water heaters you are considering. This is something we can't do for you especially since we don't know where you are located. The chart will show you the temperature rise of the water a various flow rates. Or, it may say how many fixtures it can support at a certain water inlet temperature. One word of caution though. Don't under size the heater. The guidelines they provide tend to be best case scenarios and if you read this forum a bit you'll occasionally find people complaining about the water from their tankless not getting hot enough.

Tankless heaters work differently than tank heaters. When water is flowing they can only add a certain amount of heat in the short time the water is in the heater. So, their performance depends heavily on the temperature of the water going into the heater. Say for example your heater can increase the water's temp 50f at a flow rate of 2.5 gallons per minute. Someone up north in Canada in winter may have 40f water entering the heater. When they turn on a faucet all the way the hottest the water will get might only be 90 f (40f water coming in temp + 50f temp rise from heater = 90f output water temp) regardless of how they have the thermostat on the heater set. Someone living in Miami in the summer's water going into the heater might be 70f so that same 50f temperature rise means the water from the tap could potentially be 120f.
 
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Old 08-12-19, 04:51 PM
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Welcome to the forums.

What is the gallonage of the current tank and has it been satisfactory ?
 
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Old 08-12-19, 09:21 PM
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Tankless water heater

I think it may be a 30 gallon.
 
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Old 08-13-19, 04:42 AM
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Look at the charts for the tankless water heaters you are considering. This is something we can't do for you especially since we don't know where you are located. The chart will show you the temperature rise of the water a various flow rates. Or, it may say how many fixtures it can support at a certain water inlet temperature. One word of caution though. Don't under size the heater. The guidelines they provide tend to be best case scenarios and if you read this forum a bit you'll occasionally find people complaining about the water from their tankless not getting hot enough.

Tankless heaters work differently than tank heaters. When water is flowing they can only add a certain amount of heat in the short time the water is in the heater. So, their performance depends heavily on the temperature of the water going into the heater. Say for example your heater can increase the water's temp 50f at a flow rate of 2.5 gallons per minute. Someone up north in Canada in winter may have 40f water entering the heater. When they turn on a faucet all the way the hottest the water will get might only be 90 f (40f water coming in temp + 50f temp rise from heater = 90f output water temp) regardless of how they have the thermostat on the heater set. Someone living in Miami in the summer's water going into the heater might be 70f so that same 50f temperature rise means the water from the tap could potentially be 120f.
 
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Old 08-13-19, 06:07 AM
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I live in Texas so hopefully this helps. Since I am an empty nester, I shouldn't be using too many appliances at the same time. I have been looking at the various specs for the heaters and I'm curious about the gallons per minute. What is the optimal amount? I see some deliver 1.5 gal/min upto 3 gal/min. I'll have to figure out the water's temperature. Thank you for your advice.
 
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Old 08-13-19, 08:04 AM
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Modern "normal" shower heads flow about 2.5 gallons a minute while old ones can flow much more. Kitchen faucets can flow about 2.2 gal/minute while some special high flow ones do about 4 gal/minute. Modern bathroom vanity faucets with aerators flow about 1.5 gal/minute.

For whole house use I would get a heater sized to keep up with at least two fixtures flowing at the same time. For one thing it will give you some extra margin so your shower stays nice and hot if you have an unusually cold winter. And, it's nice if you need to take a shower and you've just started the dishwasher or clothes washer.

Many manufacturers have calculators on their websites to help you choose. Here are a few:
https://www.rheem.com/tankless-elect...r-sizing-tool/
https://www.plumbingsupply.com/tankl...ing-guide.html
https://www.rinnai.us/sizing-calculator
 
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Old 08-13-19, 08:10 AM
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Thank you so much for your advice!
 
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Old 08-13-19, 10:52 AM
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When considering a tankless you might be in trouble as far as powering it if your home is total electric. Electric tankless heaters are only available in smaller sizes because of their huge power consumption. The wiring for your old, tank water heater is nowhere near large enough for an electric tankless. One solution would be to get a dinosaur (natural gas or propane) powered heater and have a gas line run or set a propane tank outside.
 
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