DIY Tankless Water Heater

[30WCF]

Anyone DIY an electric, tankless in a small 1 bath house on 100A main?

We always wash clothes on cold.

The worst I could do for usage is
1 shower 1.5-1.75 gpm
1 dishwasher don’t know, but it has to be right there.
1 Kitchen sink 1-1.25 gpm
If I run the dishwasher and kitchen sink while in the shower, that’s still only about 4-4.5 gpm.

1 laundry washer, but again, that’s always set on cold.

What’s central NCs winter rise requirements? This morning my cold tap water was 57*F. What would it be in the dead of winter? Maybe 45-50*F, for a 70* rise?

Currently running a 120v well pump and bladder tank under house in crawl space.
240v Electric tank heater is almost directly under shower.
Line to shower is 10-15’
Line to dishwasher and kitchen sink is 30-35’
Laundry is 40’, cold water usually, but the option is there.

Other utilities
LED lighting and ceiling fans
120v Gas furnace
240v AC
Washer/dryer
Dishwasher
Microwave
Refrigerator/Freezer
Electric Range/Oven
Random outlets used

I have to think a 240v 28KW 5.5gpm heater will cover all that and some. What’s the difference in if my panel can handle a 240v tank water heater vs a 240v tankless water heater?

 

[ABMax24]

Max amperage draw is the difference. A 24kw tankless pulls all of your 100 amps at full load. A tanked water heater is probably around 30 amps, so it has a recovery time but doesn't overload your panel.

My answer is no, don't do it.

 

[gthomas785]

Dude, 28 kW is massive. At 240 volts that will pull 116 amps. What is your motivation for switching to tankless? I find they are really only good at saving space. If you're trying to save energy, a tankless won't do that. If you routinely run out of hot water, you could add another tank for a lot less money and less draw on your electric.

 

[30WCF]

What happens if I put it on propane? Any gains there? I would probably have to hire someone to do the gas line, but does that change how folks feel about tankless?

 

[gthomas785]

What happens if I put it on propane? Any gains there? I would probably have to hire someone to do the gas line, but does that change how folks feel about tankless?

I still don't know what you're trying to gain here. More capacity? More efficiency? Cost savings?

If you hardly use any hot water then a tankless heater might save a little bit on standby loss. But modern tank water heaters are pretty well insulated so the saving might not pay back for a long time (not the case for gas fired tanks which have a cooling flue up the middle)

A propane tankless would not affect your electric system but has the added complexity of needing a (large) gas line and venting. So cost wise might not really pencil out depending on how much of it you can do yourself.

 

[30WCF]

Really just looking for more hot water. I get about one good shower out of the heater we have. That’s one good shower for me. If I’m in there for ten minutes, that’s a good soak. The wife and kids can stay in there for an hour each.

 

[gthomas785]

So in that case a tankless could be the right solution for you. But first did you make sure your current heater is working as intended? Ive seen heaters where the bottom element failed and the top kept going and was heating up 1/2 of the water. Can you turn up the temp any more than is already set so you're mixing in more cold at the shower valve and the hot lasts longer.

You could get a smaller tankless heater just for the shower. I don't think you need 28 kW.

Gotta wonder what are they doing for an hour in the shower if it's cold after the first 10 mins? Lol

 

[bogieb]

I haven't had an electric water heater, but that thing has to draw some juice.

Since you already have a gas furnace, running a pipe for a gas tankless might be a good alternative. I had a direct vent, tankless combi-boiler put in a couple of years ago (my 40gal gas tank heater gave up and my boiler was 30 years old), and I haven't run out of hot water yet. I will grant you that it's only 1 person here but I've run my dishwasher while taking a shower without any issues, then gone to washing bird cages in the bath tub, then done a load of laundry on hot.

 

[EatenByLimestone]

Add another water heater in series? 2 40g tanks will be rated for about 50 each. It’s screwy the way they calculate it, but drawing the water from the top gives cold water fed into the bottom time to warm. Since that water gets fed into another tank where it can get warmed more you effectively get more. Maybe up to 130 gallons?

If this is for your 2nd place, it’s adding complexity to your winterizing routine.

 

[30WCF]

So in that case a tankless could be the right solution for you. But first did you make sure your current heater is working as intended? Ive seen heaters where the bottom element failed and the top kept going and was heating up 1/2 of the water. Can you turn up the temp any more than is already set so you're mixing in more cold at the shower valve and the hot lasts longer.

You could get a smaller tankless heater just for the shower. I don't think you need 28 kW.

Gotta wonder what are they doing for an hour in the shower if it's cold after the first 10 mins? Lol

I forgot that when the kids were real small, I did turn the temp down on the tank, so that a full shot of hot water in while playing in the tub wouldn’t burn the skin.

I did think of just doing one for the shower as an option.

I don’t know what they do, but the kids come out shivering and giggle like they had a great time. I remember dad complaining about me when I was small for taking long showers. I had little green army men that lived in the bathroom drawer in a little drawstring bag mom made from a pair of old blue jeans. Me and those guys played countless hours.

 

[30WCF]

Add another water heater in series? 2 40g tanks will be rated for about 50 each. It’s screwy the way they calculate it, but drawing the water from the top gives cold water fed into the bottom time to warm. Since that water gets fed into another tank where it can get warmed more you effectively get more. Maybe up to 130 gallons?

If this is for your 2nd place, it’s adding complexity to your winterizing routine.

Primary residence.

I get what you’re saying. It has time to warm more than the tank capacity before you run out.

 

[EbS-P]

I really like our 80 gallon heatpump hot water heater. Best decision we made. Free dehumidification. Free AC in the summer. 0.5kw 95% of the time. Down side is space requirements.

 

[30WCF]

Maybe in another 10 years. We just had our furnace replaced maybe 10 years ago.

 

[gthomas785]

If you have the space, I would go for another tank piped in parallel, or a heat pump water heater piped in series with your existing water heater.

With parallel piping it's tricky to get the flow balanced so you'd need to pay attention to the amount of piping and elbows to try to get them matched up. Series piping is simpler, but places most of the heating load on the first tank with the second basically acting as a storage tank. That's not necessarily a problem depending on your usage habits and with a heat pump can save quite a bit of energy.
In my house, I have a HPWH in series with a regular tank water heater. Most of the lifting is done by the heat pump and the other tank adds storage capacity and a temp boost as needed.