House flooded and going to a tankless water heater

dlbleak

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Needs electricity like all water heaters.
We could take hot or warm showers with a conventional tank until the water cooled.
When we moved to the old house, we lost power frequently before they fixed the issue. We learned to take showers pretty soon after losing power with the water in the tank not knowing when power would come back. Even 3-4 hours later, you could still take a warm shower. Not so with tankless.
 

Aries

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Water Heater 101 class:

Tankless water heaters have an electric igniter that lights the burner when you call for hot water. No electricity, no light the burner, no hot water. Since there is no tank holding preheated water, your next shower will be cold.

Gas water heaters have a pilot light that lights the burner when the temperature of the water drops below a preset temperature. They do not depend on electricity at all. If the water in the tank is hot, you can use it until it runs out of hot water, or until it cools off (which is usually hours).

Electric water heaters heat the water with an element that is heated by electricity. The water in the tank will stay hot until used or temperature drops from sitting idle (again, usually hours), but they won't reheat without electricity.
 

HFS

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Water Heater 101 class:

Tankless water heaters have an electric igniter that lights the burner when you call for hot water. No electricity, no light the burner, no hot water. Since there is no tank holding preheated water, your next shower will be cold.

Gas water heaters have a pilot light that lights the burner when the temperature of the water drops below a preset temperature. They do not depend on electricity at all. If the water in the tank is hot, you can use it until it runs out of hot water, or until it cools off (which is usually hours).

Electric water heaters heat the water with an element that is heated by electricity. The water in the tank will stay hot until used or temperature drops from sitting idle (again, usually hours), but they won't reheat without electricity.
Has anybody else heard of the following:
For tankless water heaters and wall mounted vented room heaters (NG and propane), I have heard that if the exhaust is vented straight out through the exterior wall of the house [without going upward] you may be required to have a blower motor that cycles on when the device fires up in order to force the carbon monoxide outside the residence for safety.
I'm just curious. If this is correct, could you have a 12 volt or similar blower motor so it would still work for a while on battery during a power outage?
 

Frederick

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Has anybody else heard of the following:
For tankless water heaters and wall mounted vented room heaters (NG and propane), I have heard that if the exhaust is vented straight out through the exterior wall of the house [without going upward] you may be required to have a blower motor that cycles on when the device fires up in order to force the carbon monoxide outside the residence for safety.
I'm just curious. If this is correct, could you have a 12 volt or similar blower motor so it would still work for a while on battery during a power slavery.
Depends on installation. If its vented straight out, no. I am a licensed plumber in OK and I've installed naviens and rinnais.

I personally would always have a 40 in my house. The thing about an instant hot water heater is that there is a lot more to go wrong with it, and I've seen the bills for replacing parts in a navien water heater. You need to run a cleaning solution through the isolation valves every 6 months but that's not a big deal. If you live on well water, I would not get a thankless. The high calcium content would eat through your heat exchanger very quickly. You can get a water softener, but that only mitigates the issue. Personally I would change my annode rods every decade or so and flush my water heater every 6 months if I lived in the country. Ymmv


A navien is cool but personally 30 to 40 years on a 40 gallon tank is a no Brainer for me personally. Only makes sense if you have a specific need to go tankless imo.
 

Frederick

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It takes very little gas. Your 80s house will be just fine. I’ve installed more hot water tanks than I can remember. Gas and electric. Gas in houses going back to the 40s because their electrical panels can’t support anything else and investors are cheap as hell.

...maybe there's a model I'm not familiar with but most tankless w/hs do indeed burn less gas overall and are more efficient, but burn gas a lot more quickly in a shorter period of time...they have a higher Btu rating. So compared to a normal 40 gallon you'd either need to run a 3/4 gas line or have much higher pressure compared to a 40.
 

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