If you have a tankless water heater or "hot water on demand" how do you like it?

I have a tank, but my girlfriend has a tankless heater in her house. It is pretty cool to turn on the shower or the water and have it be hot right away. She says it is more efficient than when she had a tank. Since it is only her, and occasionally me, in her house it makes more sense. Would have a lot wasted energy keeping water in a tank that sat around all day.
So the real question is how much hot water do you use in a day, and how much do you need at one time.
You can look up the limitations of a tankless heater. They can’t keep up with excessive demand at once.
But if you fit the criteria, you could save a lot of money. When the tank in my place goes bad in a few years, I will probably replace it with tankless. But it’s just me, in my place so I don’t use a lot of hot water.

The cost in having a tank water heater is it is using energy to keep a 40 or 50 gallon tank hot all the time. We have a tankless at our house and love it.

The furnace you are talking about is a whole house one?

Heating hot water for baseboard heating?

I have two furnaces. A small one heats baseboard heating in the modern addition and the big old one that is the one that needs replacing soon heats steam radiators in the older parts (about 6 rooms.)

We have an electric heater for our kitchen sink. I’ve had it now for almost 8 years and still don’t know if I like it or not. On one hand, you turn on hot water and it is almost immediately hot. But the odd part I’m still not sure about is that it is burning hot for about 20 seconds and then starts to cool down for another 30–45 seconds, getting almost tepid, then gets hot again and seems to stay that way. Really odd. all in all, I guess I like it. Not sure if I would want one for my shower.

Do tankless heaters use electricity to heat the water?

Some are gas and some are electric, my uncle had a tankless electric in the 1960’s.

I assume since they were suggesting a combo with the gas furnace, this would be gas.

Tankless is not hot on demand at the tap. If the tankless is replacing your tank, the water still needs to run through the pipes, so you still need to run out the cold water sitting in the pipes before the hot water comes through. There is a such thing as hot in demand, but then it is a small unit right at the point of the sink or shower that heats the water right before it runs out of the faucet.

Positives about tankless are lower gas bills and the water will run hot forever, you won’t run out if you take a long shower, or if ten people take ten showers in a row.

Negative is it usually costs more initially than a tank, it doesn’t hold any hot water, so if you lose power you won’t have a couple of days of warm water like a tank.

Gas tankless do use electricity. They have digital read outs, and maybe something else is electric in there controlling everything. If you lose power you have no hot water.

I have mixed feelings about the whole thing. Is there a big cost difference initially where you live?

The thing about instant hot water is that the device must be relatively close to whichever outlet or tap is to be used. In a big house the delay in hot water is due to the run of pipe from the heater to the taps. The hot water is cooled from contact with the cold pipes and you must in effect bring the pipes up to temperature the full length of the run before you will have water from the tap as hot as the water in the heater. In our house there are runs of pipe of 40 feet or more. And the piece of crap flow restrictor faucet in the fancy new bathroom vanity basin is the furthest outlet from the heater. It takes better than 3 minutes for the water to come up to hot in that basin, but the shower 8 feet away on the same line will be scalding hot in less than 30 seconds.

I have a hot water on demand system in my flat and I can recommend it. It is unusual in that it uses a heat exchanger rather than a hot water heater or boiler. It gives virtually instant and limitless hot water on demand and is economical to run. I used to pay to heat up water in a tank which I didn’t always use. My flat is quite small and compact and it doesn’t take long for the hot water to reach my kitchen and bathroom taps.