Tankless water heater

I have a water heater going bad on me, so I have to replace it with something comparable or a tankless heater. I kept hearing people telling me the tankless ones cannot heat it fast enough to give hot enough water so I am wondering if this is because it's not done right or really there is a truth to this.
I am located in Miami Florida so the coldest temperature during the year would be like 35-40 degrees F. I have 200amps electric service. I believe the highest demand for hot water when the master bath and second bath's showers are both on, and at the same time the washer is running with hot water. My baths are pretty simple, no additional nozzles. Is there a way to compute if a tankless heater will work? and if so what model and size is recommended?
Thanks in advance,
MC
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says...

Calculate the flow rates of everything you need on at once -- how many gallons per minute for the showers, how much for the wash, etc. Find a heater that puts out at least that much hot water continuously, and you should have enough hot water. Our Takagi natural gas tankless puts out enough to run the shower, dishwasher, and washing machine at the same time, and it's not the largest unit on the market by far.
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I put a tankless into my home and very happy about it. One problem that I had was my water pressure was on the low end (25psi) and the main shower flow was marginal. I had to remove the flow limiter to the shower head and the unit worked fine. These things need a minimum flow to engage the heater. All in all I will only use flash heaters in the future. Higher initial cost, lower energy cost, lower maintenance and they should last longer. Which should equate to an overall lower cost of ownership. You never run out of hot water. However if you have an electric one and power goes out you don't have the tank of hot water to tide you over until electric comes back.
As far as capacity you need to look at the specification of the unit. The flash heaters raise the water temperature based on flow rates and the amount of BTUs they generate. Living in Miami would be beneficial as your water temperatures would be high to begin with. Take a look at http://www.controlledenergy.com/ for more information. The are one of the main distributors of flash heaters. I bought my system from home depot because I needed it immediately when mine failed. There are many other online business that sell these.
The other issue with the gas heaters is that some change the venting to a single wall pipe under pressure. I would use the manufacter's recommended materials or better. With an electric this is a non issue.
ken
miamicuse wrote:

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Thanks Ken:
That was very helpful information. Being in Miami we do have the occasional power outages that comes with hurricanes and tropical storms so that may be an issue, so may be I better check with the boss, uhh...my wife...and see if this is ok.
MC

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