Experience with tankless water heater?

[T_Bone_TL]

I have an electric water heater up in our mountain place. It looks like it might be as old as the building, which went up in ‘82. It works fine but I figure it could go any time, in which case I want to look at tankless since we aren’t always up there.

Which brings me to my question - how much of an issue is groundwater temperature coming into the unit? Our place is at 7400 feet in the Rockies and the water coming out of the tap is butt cold in the winter.

Incoming temperature matters. Especially if you're thinking electric tankless. Unlike a tank, where it can heat the water until it's hot, it's got a fixed amount of power and for any given flow rate it can raise the incoming temperature a set number of degrees. The same is true of gas, but gas tankless tend to have a lot more input power available than electric tankless do. Unless you have a 400A service and practically no real loads on it, think replacement tank heater for electric.

Say you have enough capacity (may not be true) to run a 120A tankless electric. 120A x 240V = 28,800W, or 28.8 KW (typically 3 sets of 40A double-pole breakers, so if you don't have 6 slots free you'll need a new breaker panel to put them in.)

If that ran for an hour, if could heat 98,000 lbs of water one degree F, or 1092 lbs 90 degrees F (butt-cold mountain to nice and hot for a shower) which is about 131 gallons. In a hour. So a flow rate of 2.2 gallons per minute. Perhaps you only need 80 degrees rise, where that would get you to 2.4 gallons per minute. 70 degree rise would get you to 2.8 GPM

If someone washes their hands or the dishes or otherwise uues hot water at the same time while you're in the shower, the flow rate will go up and the temperature will go down as a result.

If you can only support 60A on your service, cut those flow rates in half. Meanwhile your 30A (typical) heater can, by virtue of storage, make water as hot as you like that you can use 30 or 40 or 50 gallons of as fast as you like (after which it needs some time to catch up.)

If you're not always up there, shut the tank off when you leave and turn it on when you arrive (or make your place hackable and turn it on before you arrive.)

 

[TOOL460002]

I think the quality of the water is important. If your water is hard and scaly, it builds up in the heater and can damage it.

I am both on my own well and have a tankless gas heater. Zero issues and, thus far, zero maintenance. Aside from just water softening and general well/plumbing health, I haven't touched the thing. Has worked perfect for a decade. If it explodes I'll call whoever made it or buy another one. Big fan. No cold water (unless I am in a power outtage, which I occasionally am...).

 

[FRoss6788]

The most important maintenance tankless heaters need is an annual flush to descale the heating coil which is (typically) 1/2" copper tubing. If neglected it scale can build up inside and reduce the flow of water.

 

[Altitude]

Incoming temperature matters. Especially if you're thinking electric tankless. Unlike a tank, where it can heat the water until it's hot, it's got a fixed amount of power and for any given flow rate it can raise the incoming temperature a set number of degrees. The same is true of gas, but gas tankless tend to have a lot more input power available than electric tankless do. Unless you have a 400A service and practically no real loads on it, think replacement tank heater for electric.

Say you have enough capacity (may not be true) to run a 120A tankless electric. 120A x 240V = 28,800W, or 28.8 KW (typically 3 sets of 40A double-pole breakers, so if you don't have 6 slots free you'll need a new breaker panel to put them in.)

If that ran for an hour, if could heat 98,000 lbs of water one degree F, or 1092 lbs 90 degrees F (butt-cold mountain to nice and hot for a shower) which is about 131 gallons. In a hour. So a flow rate of 2.2 gallons per minute. Perhaps you only need 80 degrees rise, where that would get you to 2.4 gallons per minute. 70 degree rise would get you to 2.8 GPM

If someone washes their hands or the dishes or otherwise uues hot water at the same time while you're in the shower, the flow rate will go up and the temperature will go down as a result.

If you can only support 60A on your service, cut those flow rates in half. Meanwhile your 30A (typical) heater can, by virtue of storage, make water as hot as you like that you can use 30 or 40 or 50 gallons of as fast as you like (after which it needs some time to catch up.)

If you're not always up there, shut the tank off when you leave and turn it on when you arrive (or make your place hackable and turn it on before you arrive.)

Thanks. Great info there.

 

[badinage]

I'm not going to wade in on the efficiencies vs quirks and tradeoffs of daily use, you can get plenty of that with an online search. ...which I strongly encourage. Before you get to the point of signing-up for tankless, here's what the sales brochure doesn't say:

If it's gas, how are you going to vent it? May be simple as the tank-type gas-fired unit you're replacing, might not be though. Find out FIRST.

If it's electric: The electric service to the unit, as @T_Bone_TL points out, will need to be MUCH larger than the one that ran to your tank-type electric. Do you have the capacity? How difficult will it be to get the much larger wire from your panel to the install point of the new tankless? Might be easy, might be a bunch of wall in the way to snake those much larger wires through and no way around it. Find out FIRST.

Also: Both gas and electric on demand will have a computer-board in them. Your tank unit probably doesn't. When your computer board goes down, does the guy you bought it from have swap-outs/replacements on his truck? Often not, then it's a day or two, maybe three to overnight the repair part, assuming it's in stock, which they "always are" except, of course, when there are "chip shortages" and "supply chain interruptions"...

I'm not trying to sell anybody either way. Just talk FIRST about the stuff nobody ever talks about.

 

[fhm555]

When I was in Okinawa, I lived off base for a while and the local houses pretty much all had natural gas tankless heaters. It was usually mounted on a wall in the bathroom, a wall shared with the kitchen so the hot water plumbing was just to the shower and sink in the bath and sink in the kitchen. That kept plumbing simple and short. I loved them for the shower. Full hot water within a few seconds of turning the tap on and supply never lagged behind demand, but our unit couldn't keep up if you were running the shower and one or both sinks. It could carry both sinks at once no problem, but not the shower and a sink.
If you couldn't put them on a common wall between the kitchen and bath, the most used alternative was a separate, smaller unit for the kitchen.

 

[claudel]

Ours works good just takes time for the hot water to reach the taps that are further away from the unit in the house

I've had one for ~ 6 years now. City gas, no real issues.

If I was to redo, I'd use several smaller units, one for kitchen, one for bathroom.

The one I have now is in the bathroom ( takes up a good bit of space ) and seems to waste a lot of water warming up to far away places.

City water bills can be expensive.

I added a scale filter to the cold water input. This thread reminds me it's time to service & replace filters.

Probably a good time to replace the RO drinking water filters, too.

 

[P. Aaron]

The ads I'm seeing while reading this (helpful) thread:

 

[Green Hornet]

We have a gas Navian in a newly built house. We can have 2 showers & washer going and it holds up fine. The temp is set at 120°.
Just remember to perform regular maintainence on it. Or they can do service it too- it is worth it.

 

[Gaolee]

I am both on my own well and have a tankless gas heater. Zero issues and, thus far, zero maintenance. Aside from just water softening and general well/plumbing health, I haven't touched the thing. Has worked perfect for a decade. If it explodes I'll call whoever made it or buy another one. Big fan. No cold water (unless I am in a power outtage, which I occasionally am...).

Is yours electric or gas?

Our current unit is gas, but I can see the advantages of having much smaller electric units for different parts of the house in time. We are thinking about solar panels and ditching our furnace for a heat pump and electric tankless units when we put on a new roof in five years or so. It's probably pie in the sky stuff, since it would be way too expensive. But a man can dream, right? Gawd! I dream about electric tankless water heaters. I must be old.

One other benefit of tankless is that they are not near as big as a tank. We got rid of a big tank that sat in the middle of the basement and was an obstacle to just about everything. Now, we have the tankless unit attached to the basement wall and venting out the side of the house along with the high efficiency furnace. It freed up a huge amount of space because it isn't in the way of everything any more.

 

[TOOL460002]

Is yours electric or gas?

Our current unit is gas, but I can see the advantages of having much smaller electric units for different parts of the house in time. We are thinking about solar panels and ditching our furnace for a heat pump and electric tankless units when we put on a new roof in five years or so. It's probably pie in the sky stuff, since it would be way too expensive. But a man can dream, right? Gawd! I dream about electric tankless water heaters. I must be old.

One other benefit of tankless is that they are not near as big as a tank. We got rid of a big tank that sat in the middle of the basement and was an obstacle to just about everything. Now, we have the tankless unit attached to the basement wall and venting out the side of the house along with the high efficiency furnace. It freed up a huge amount of space because it isn't in the way of everything any more.

Gas: Takagi t-kjr2-os to be precise. Tiny. Outdoor. And, while I am not sure how I never noticed it before, it has my new favorite warning symbol/danger cartoon:

That looks like the kinda thing you don't want to survive.