Need a new water heater - go tankless?

[Eug]

As long as you realize that you'll never save enough energy to justify the high purchase price, get one.

I would have stuck with a tank, but didn't have enough room for a 75 gallon tank. I have a big house, and a bathroom with a large soaker tub. A 50 gallon tank wouldn't cut it, but the utility rooms didn't have enough height for a 75 with the appropriate power-vented exhaust piping.

But also remember that if there's a power outage, no hot water at all. A storage tank water heater will provide some hot water for a few days unless the area's water tank is empty/compromised.

I have the tankless plugged into a <$200 1500 VA sine wave consumer UPS. So, even in a power outage, I have hot water. Taking a hot shower in a power outage is not an issue, at least early on in the power outage until the UPS runs out. More importantly, the water doesn't go cold in the middle of a shower, if I happen to be taking a shower when the power outage hits.

However, even without the UPS I get about 2 minutes of hot to warm water before it goes cold, because I have a 6 gallon electric tank after the tankless. (Incoming water is hot from the tankless to the electric tank, so the tank doesn't use much electricity to heat the water, just to keep it hot.)

This pic isn't mine, but it's the same idea:

 

[NoTine42]

I would have stuck with a tank, but didn't have enough room for a 75 gallon tank. I have a big house, and a bathroom with a large soaker tub. A 50 gallon tank wouldn't cut it, but the utility rooms didn't have enough height for a 75 with the appropriate power-vented exhaust piping.


I have the tankless plugged into a <$200 1500 VA sine wave consumer UPS. So, even in a power outage, I have hot water. Taking a hot shower in a power outage is not an issue, at least early on in the power outage until the UPS runs out. More importantly, the water doesn't go cold in the middle of a shower, if I happen to be taking a shower when the power outage hits.

However, even without the UPS I get about 2 minutes of hot to warm water before it goes cold, because I have a 6 gallon electric tank after the tankless. (Incoming water is hot from the tankless to the electric tank, so the tank doesn't use much electricity to heat the water, just to keep it hot.)

This pic isn't mine, but it's the same idea:

That's a nice solution to the biggest comfort problem with tankless.

If you have really cold (40-50 degree), cold water, tankless is much less than ideal for quickly washing your hands.
By the time my tankless fired up and started running at full temp, a quart or 2 of ice cold water was running through the "hot" pipes. So I had an odd room temp > ice cold > hot comming out of the faucet while washing hands. (A normal water heater gradually ramps up from room temp to hot...and I preferred that)

I've seen elaborate systems to mitigate that icy blast from tankless systems: motion sensor in the bathroom + hot water return pipe + recirculating pump so the motion sensor triggers the pump so the tankless can start running and actually have hot water at the faucet before you turn it on...

 

[Eug]

If you have really cold (40-50 degree), cold water, tankless is much less than ideal for quickly washing your hands.
By the time my tankless fired up and started running at full temp, a quart or 2 of ice cold water was running through the "hot" pipes. So I had an odd room temp > ice cold > hot comming out of the faucet while washing hands. (A normal water heater gradually ramps up from room temp to hot...and I preferred that)

I've seen elaborate systems to mitigate that icy blast from tankless systems: motion sensor in the bathroom + hot water return pipe + recirculating pump so the motion sensor triggers the pump so the tankless can start running and actually have hot water at the faucet before you turn it on...

You're talking about the cold water sandwich, except it's worse for a shower.

If someone takes a shower in your house, you have hot water in your hot pipes. In my house, which is quite large, that's a lot of hot water.

So, 5 minutes later you decide to take a shower too. You turn on the shower and you'll have a nice hot shower, and then 30 s later you'll have ice cold water, and then hot water again.

I got the 6 gallon tank specifically for this reason, and also to decrease the time to hot water. Interestingly, some brands of "tankless" water heaters actually include a 2 gallon tank built-in for these reasons.

For sinks, some people get point of use tanks. Tiny tanks just for the sink, situated underneath the sink that run on electrical power.

 

[americanwashing]

Very helpful. Thanks guys for sharing your experience!

 

[MongGrel]

I wouldn't, but have at it if ya want to.

Unless you want to buy multiple ones like mentioned all over.

 

[JoeBleed]

With this being an old thread, maybe the OP will respond to say what he ended up doing.

I've had an idea i've wanted to try, but never have, that would work well for someone that lived alone or maybe just two people. Maybe you guys and tell me what you think.

1. replace old/broken water heater with a 10-20 gallon tank heater
2. if electric, have a switch setup for it, if gas, figure out a way to switch that on and off easily.
3. switch the heater off when not in use and switch it on maybe 20 minutes before use.

Granted, this would require a little planning and someone that doesn't want or care about hot water to wash hands.

I ran across this setup when traveling some 15 years ago. except it wasn't switched, you had to plug it up and unplug it when done. I like the concept for me. though i wonder about bacteria build up in the tank if it's fed by a well. such as in my case. I already think i have a small issue with that because if infrequent use of hot water.

 

[imagoon]

It would depend on how "infrequent" the use is. In the US, to avoid Legionnaires' disease you need to keep the water at 120 degrees F for at least 2 hours. 120F is the typical holding temp for hot water. You need 16.6 BTU to heat a gallon of water 1F. Typically inlet temps are around 55 degrees. So you would need at least 1079 BTU per degree to raise that water to 120F (16.6 BTU x 8.3lbs x 65 degrees raised.)

This means your tiny (considered too small for a home by the way) 20 gallon water heater would need at least a rating of 21580BTU/hr to raise the temp of the water to 120F in 1 hour or 64740 BTU/hr in 20 minutes. Most small units however are not that high of a power. A typical 20 gallon is going to be electric and around 2000watts which roughly equates to 7000 BTU/hr. They are designed for sinks and considered too small for showers.

Honestly to me it sounds like you should get the proper sized tank and get a replacement with a decent R value to insulate the tank and pipes.

--edit--

BTU -> [rating of] BTU/hr where needed for clarity. BTU of water heaters is listed as "BTU / hr" but this isn't always obvious.

 

[echo4747]

Also check with your electric utility company and see if there is a demand charge. At certain times usually during the daytime you may be billed at a different rate plus a demand(premium) charge for the spike that heater will cause when making hot water. You may not save anything vs a storage type heater that heats during off-peak times

 

[tortillasoup]

I got the 6 gallon tank specifically for this reason, and also to decrease the time to hot water. Interestingly, some brands of "tankless" water heaters actually include a 2 gallon tank built-in for these reasons.

For sinks, some people get point of use tanks. Tiny tanks just for the sink, situated underneath the sink that run on electrical power.

Yes unfortunately though, the "tankless" water heaters with a small 2 gallon tank have a pilot light and the 2 gallon tank turns out to be UNinsulated, therefore increasing the consumption over a conventional water heater. The efficiency of the on demand water heaters with small "buffer tank" are extremely poor.

 

[mick12155]

Ohh! It's very old post for me.

But anyway, What a great in information shared here. Thanks all.

-------------
Thanks

 

[Jeff7181]

I happened to see this when asking for other plumbing advice here and saw that someone had asked for an update.

Unfortunately, there's no real update to give... while trying to make a decision, I actually ended up selling the condo and moving out before doing anything with the water heater.

 

[zinfamous]

I happened to see this when asking for other plumbing advice here and saw that someone had asked for an update.

Unfortunately, there's no real update to give... while trying to make a decision, I actually ended up selling the condo and moving out before doing anything with the water heater.

well, that's one solution!

 

[Jeff7181]

well, that's one solution!

Yeah, the furnace filter in my new house is getting dirty, so I'm house hunting again!

 

[LoveTheSouth]

Thanks everyone for sharing their experiences, I thought I would also chime in, having done this in a condo before.

First of all, so important to know what the incoming water temperature is, that will really impact what GPM rate you'll get and how much power you'll want in a tankless unit. If natural gas is an option, it will be cheaper (for energy, but more up front) and you could easily run all your faucets simltaneously (according to this water heater website)

I got the ecosmart electric unit and I have to say that i'm a little disappointed in it. If the dishwasher is running, I can't take a shower which has been pretty annoying at times, one of those things you don't notice until you're paying attention.

Anyway, this is an older post so you probably made your choice, but for further forum lurkers still using this thread

 

[Scarpozzi]

Thanks everyone for sharing their experiences, I thought I would also chime in, having done this in a condo before.

First of all, so important to know what the incoming water temperature is, that will really impact what GPM rate you'll get and how much power you'll want in a tankless unit. If natural gas is an option, it will be cheaper (for energy, but more up front) and you could easily run all your faucets simltaneously (according to this water heater website)

I got the ecosmart electric unit and I have to say that i'm a little disappointed in it. If the dishwasher is running, I can't take a shower which has been pretty annoying at times, one of those things you don't notice until you're paying attention.

Anyway, this is an older post so you probably made your choice, but for further forum lurkers still using this thread

How many gpm is your electric unit? It sounds like it's undersized or underperforming... At Lowes and Home Depot, they used to have a tankless water heater guide map to help you choose a powerful enough unit to compensate for the water feed temp. My gas unit is an 8.0 gpm Rinnai. I lose water pressure by running too many things simultaneously before I lose temperature. One of these days, I may adjust my line pressure and fix that problem.