Author Topic: Tankless waterheater in MN  (Read 968 times)

TheAnonOne

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Tankless waterheater in MN
« on: January 06, 2022, 11:13:53 AM »
Anyone have experience with tankless in northern climates? We have a 75 gal traditional tank going out. It's a big house, with big(ish) water needs. Right now it's only two people who are wasteful with hot water, but in the future I want space to grow.

It looks like the largest ones you can buy are about 199kBTU 11GPM which is enough to run (they say) two showers at the same time. Theoretically that sounds OK but I worry it's two lukewarm showers vs. two scalding-hot-medical-grade showers.

Input appreciated!

FYI: Been looking at this one, a replacement 75gal is $1350, so the price's are about the same. Self install both ways...

https://www.homedepot.com/p/Rheem-Performance-Platinum-11-GPM-Natural-Gas-High-Efficiency-Indoor-Recirculating-Tankless-Water-Heater-ECOH200DVRHLN/303786842#overlay


yachi

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Re: Tankless waterheater in MN
« Reply #1 on: January 06, 2022, 11:32:22 AM »
You can do some math if you measure your cold water temperature.
New showerheads have a maximum 2.5 GPM

At 8.5 GPM, this unit provides a 45°F Rise
At 5.0 GPM, it provides a 77°F Rise

So if your cold water is 43°F, then this unit should be able to raise that to 120°F, and provide both showers with enough flow to properly scald two occupants.  5 minutes at 120°F will provide the third-degree burns you're looking for.

As long as your water temperature is above freezing (!?) the 77°F rise should provide a shower above the threshold of human pain (106°F to 108°F).

TheAnonOne

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Re: Tankless waterheater in MN
« Reply #2 on: January 06, 2022, 12:09:54 PM »
You can do some math if you measure your cold water temperature.
New showerheads have a maximum 2.5 GPM

At 8.5 GPM, this unit provides a 45°F Rise
At 5.0 GPM, it provides a 77°F Rise

So if your cold water is 43°F, then this unit should be able to raise that to 120°F, and provide both showers with enough flow to properly scald two occupants.  5 minutes at 120°F will provide the third-degree burns you're looking for.

As long as your water temperature is above freezing (!?) the 77°F rise should provide a shower above the threshold of human pain (106°F to 108°F).

This is awesome math.

The other concern is a drop in water pressure to the house. I can damn near cut granite with my shower, I wouldn't want that to change.

RWD

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Re: Tankless waterheater in MN
« Reply #3 on: January 06, 2022, 12:33:19 PM »
Water pressure hasn't been a problem with our tankless heater, though I don't like super high pressure showers anyway.

The only annoyance we've experienced is the minimum flow requirements. The heater only activates if enough water is flowing so if you want just a little bit of hot water it will come out completely cold. This manifests mostly when trying to wash dishes with warm water (hot enough for washing but not fully hand-scalding hot). And I've had a few showers in the summer where I had a hard time getting the water as cool as I wanted without the hot water heater shutting off entirely (very unlikely you would run into this in northern climates).

yachi

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Re: Tankless waterheater in MN
« Reply #4 on: January 06, 2022, 02:27:42 PM »
You can do some math if you measure your cold water temperature.
New showerheads have a maximum 2.5 GPM

At 8.5 GPM, this unit provides a 45°F Rise
At 5.0 GPM, it provides a 77°F Rise

So if your cold water is 43°F, then this unit should be able to raise that to 120°F, and provide both showers with enough flow to properly scald two occupants.  5 minutes at 120°F will provide the third-degree burns you're looking for.

As long as your water temperature is above freezing (!?) the 77°F rise should provide a shower above the threshold of human pain (106°F to 108°F).

This is awesome math.

The other concern is a drop in water pressure to the house. I can damn near cut granite with my shower, I wouldn't want that to change.

There's a pressure drop chart on page 49 of the instructions.  You're looking to lose maybe 4 psi at 2.5 GPM, and maybe 12 psi at 5 GPM.  Keep in mind even though your showerhead can do 2.5 GPM, you'll likely be using a mix of hot and cold water, so you should see losses lower than this.  The unit can handle a maximum pressure of 70 psi, so you'll want to unsure you house's water pressure is lower than this.  It should be lower than this, unless you're actually cutting granite.  Code limits residential pressure to 80 psi, and requires you have a PRV installed if it's higher than that.  Pressure that's too high can damage valve seals and cause water hammer effects when shutting off faucets.

Jon Bon

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Re: Tankless waterheater in MN
« Reply #5 on: January 06, 2022, 07:31:17 PM »
How's your gas meter?

In my neck of the woods they usually top out at 250 btus if I remember correctly. The tankless would put us over and that would require a bigger meter at my cost as well as a new line to the house and re-piping the whole house! Again it was a while ago.

Water heater 200
Furnace 80
stove/dryer/fireplace/grill/etc

You can see where this goes. Its one of the reason those things are expensive as hell to install. I had an electric one. It was pretty great but an energy hog and it just encourages you to take longer hotter showers IMO.

Have you looked into a steam shower? Honestly might be cheaper then re-piping your whole house.



Morning Glory

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Re: Tankless waterheater in MN
« Reply #6 on: January 06, 2022, 07:47:52 PM »
I had an energy audit when I lived in MN and the guy advised me that we would not be happy with tankless. I was really surprised because the upstairs shower took forever to warm up. This was in 2014 ish so it's possible they have improved since then.  I was also on well water which runs a little colder than town water.

reeshau

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Re: Tankless waterheater in MN
« Reply #7 on: January 07, 2022, 05:53:57 AM »
I will simply say that my brother, who does HVAC for a living in MN, has a tankless water heater.  He used to scoff at them, but changed his mind several years ago.

TheAnonOne

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Re: Tankless waterheater in MN
« Reply #8 on: January 07, 2022, 09:10:54 AM »
How's your gas meter?

In my neck of the woods they usually top out at 250 btus if I remember correctly. The tankless would put us over and that would require a bigger meter at my cost as well as a new line to the house and re-piping the whole house! Again it was a while ago.

Water heater 200
Furnace 80
stove/dryer/fireplace/grill/etc

You can see where this goes. Its one of the reason those things are expensive as hell to install. I had an electric one. It was pretty great but an energy hog and it just encourages you to take longer hotter showers IMO.

Have you looked into a steam shower? Honestly might be cheaper then re-piping your whole house.

Is there an easy way to check this?

Given that it's a northern 'large' home, my guess is that we can supply 200k BTU, but unsure if furnace and heater are on at the same time?

yachi

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Re: Tankless waterheater in MN
« Reply #9 on: January 07, 2022, 09:49:13 AM »
How's your gas meter?

In my neck of the woods they usually top out at 250 btus if I remember correctly. The tankless would put us over and that would require a bigger meter at my cost as well as a new line to the house and re-piping the whole house! Again it was a while ago.

Water heater 200
Furnace 80
stove/dryer/fireplace/grill/etc

You can see where this goes. Its one of the reason those things are expensive as hell to install. I had an electric one. It was pretty great but an energy hog and it just encourages you to take longer hotter showers IMO.

Have you looked into a steam shower? Honestly might be cheaper then re-piping your whole house.

Is there an easy way to check this?

Given that it's a northern 'large' home, my guess is that we can supply 200k BTU, but unsure if furnace and heater are on at the same time?

Your meter should have a tag with the information on it, or a model number you could Google for information.  Your gas company owns the meter, so you could call and ask them what the standard meter can supply.

For pipe inside you house, Page 40 & 41 of the installation instructions have tables to estimate the capacity different pipe sizes can provide for various lengths.

Jon Bon

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Re: Tankless waterheater in MN
« Reply #10 on: January 07, 2022, 10:16:50 AM »
How's your gas meter?

In my neck of the woods they usually top out at 250 btus if I remember correctly. The tankless would put us over and that would require a bigger meter at my cost as well as a new line to the house and re-piping the whole house! Again it was a while ago.

Water heater 200
Furnace 80
stove/dryer/fireplace/grill/etc

You can see where this goes. Its one of the reason those things are expensive as hell to install. I had an electric one. It was pretty great but an energy hog and it just encourages you to take longer hotter showers IMO.

Have you looked into a steam shower? Honestly might be cheaper then re-piping your whole house.

Is there an easy way to check this?

Given that it's a northern 'large' home, my guess is that we can supply 200k BTU, but unsure if furnace and heater are on at the same time?

Your meter should have a tag with the information on it, or a model number you could Google for information.  Your gas company owns the meter, so you could call and ask them what the standard meter can supply.

For pipe inside you house, Page 40 & 41 of the installation instructions have tables to estimate the capacity different pipe sizes can provide for various lengths.

Correct. In general you can simply google the model number and it will tell you.

The way they do it is they assume every gas appliance you have is running full out. So if that puts you >250 you need to upsize. Do you have any other gas appliances in your house? Stove, dryer, fireplace, grill etc.

I put in a new direct vent 75 gallon hot water tanks. For me it was a good compromise. Its not quite tankless but I have no run out of hot water yet.

IMO it is one of the reasons we don't see more of these installed. In the south you can get away with an electric one because it does not need nearly as much temperature gain. But in zones 4-6 the water is pretty cold and it takes a ton of energy to get it warmed up.


TheAnonOne

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Re: Tankless waterheater in MN
« Reply #11 on: January 11, 2022, 10:03:14 AM »
How's your gas meter?

In my neck of the woods they usually top out at 250 btus if I remember correctly. The tankless would put us over and that would require a bigger meter at my cost as well as a new line to the house and re-piping the whole house! Again it was a while ago.

Water heater 200
Furnace 80
stove/dryer/fireplace/grill/etc

You can see where this goes. Its one of the reason those things are expensive as hell to install. I had an electric one. It was pretty great but an energy hog and it just encourages you to take longer hotter showers IMO.

Have you looked into a steam shower? Honestly might be cheaper then re-piping your whole house.

Is there an easy way to check this?

Given that it's a northern 'large' home, my guess is that we can supply 200k BTU, but unsure if furnace and heater are on at the same time?

Your meter should have a tag with the information on it, or a model number you could Google for information.  Your gas company owns the meter, so you could call and ask them what the standard meter can supply.

For pipe inside you house, Page 40 & 41 of the installation instructions have tables to estimate the capacity different pipe sizes can provide for various lengths.

Correct. In general you can simply google the model number and it will tell you.

The way they do it is they assume every gas appliance you have is running full out. So if that puts you >250 you need to upsize. Do you have any other gas appliances in your house? Stove, dryer, fireplace, grill etc.

I put in a new direct vent 75 gallon hot water tanks. For me it was a good compromise. Its not quite tankless but I have no run out of hot water yet.

IMO it is one of the reasons we don't see more of these installed. In the south you can get away with an electric one because it does not need nearly as much temperature gain. But in zones 4-6 the water is pretty cold and it takes a ton of energy to get it warmed up.


1. This is common in MN, but, we have NatGas furnace, stove, water heater, 2 fireplaces, deck stuff (though only runs in summer). It "LOOKS" like the gas into the house is only 1/2" piping which seems "small" for a 4k sqft palace.

2. Looks like these are interesting but, at an estimated $20 annual savings for a $600 premium seems inefficient.