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Tankless water heater in an ADU for T-24

arthurp92

arthurp92

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Joined
Oct 21, 2021
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2
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Sacramento
Building new, or converting existing detached garages to accessory dwelling units clients have been asking for tankless water heaters, but it cant seem to pass Title 24 CF1R energy requirements. Anyone been able to have a workaround to meet this code? No gas all electric builds, in California.
 
If you're trying to install a tankless electric water heater prescriptively then no. If you're using the performance method (computer based modeling resulting in an energy report) then it may be possible, but that would be up to the person entering things into the computer to make them work. Chances are it would include a relatively large amount of PV to offset the energy budget.
 
Interestingly I had this same question from someone who's building a new ADU behind their house and wants to go all electric as the trends are indicating. On-demand water heaters are popular right now, but the really only make sense for gas. Why? Because "the average electric tankless water heater needs at least 120 amps to operate" vs. a tank style which can operate off of 30-40 amps. The reason being with a tank it can gradually heat the water instead of all at once.

Even with a standard electric tank heater it appears that you can't use the prescriptively, but again if you get an energy report they can usually make it work. Most new construction requires solar now anyways and every new construction project I've seen uses an energy report. That report shows the minimum solar based on the TDV energy budget which will vary based on how the house is designed, such as what type of water heating system is used.

The exception there appears to be a heat-pump water heater. They can be used prescriptively.

For reference 2019 CA Energy Code Subchapter 8 section 150.1 (c)(8)
 
I’m not much good when it comes to energy code so don’t take what I say as absolute truth. I don’t know but I’ve been told that California banned recirculating systems for residential hot water. I also recall that in the near future gas water heaters will be banned and electric heat pump water heaters will be the norm. I realize how dumb that sounds but this is California. So it should not come as a surprise.

Climate change activists want everybody but them to take cold showers. On top of that there is a push to downsize police departments. Once everything is electric people will be broke, they will smell awful and have a bad attitude. What could go wrong?
 
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CA Energy Code is a pain in the but. It was designed with the intention that people could build prescriptively but in my four years I have seen not one new construction "take advantage" of that path. Intentions aside it has created a niche market for energy consultants to model homes and provide performance models that tells builders what the have to use. Then they want all of these special inspections that local building departments aren't equipped to provide so another niche market has been created for HERS raters, and now home builders have yet another step (an expensive one) they have to take to pass their inspections. Since the Energy Commission has made these new requirements, and imposed upon local jurisdictions to enforce them, we are now supposed to log into some database and see the status of each project and request reports and certificates of installation and blah blah blah, just more regulatory BS. And of course our bosses and supervisors don't know what the requirements are so they don't know how to staff and train for these requirements, builders don't know the requirements so they ask us and we're left to look like the incompetent governmental employees that are left to enforce these new requirements. And then you get these car salesmen type of groups that sell local councils and committees on Reach Codes or similar measures that allow "a local building energy code that “reaches” beyond the state minimum requirements for energy use in building design and construction, creating opportunities for local governments to lead the way on clean air, climate solutions, and the renewable energy economy, while creating roadmaps for other local..." blah blah blah as if our states energy code wasn't already strict enough. Now houses are built so tight that people are required to add whole HRV systems because no the indoor air pollution is out of control.

Sorry rant over...
 
Thanks Joe for noting the Performance method for an electric Water Heater.
For the Prescriptive, don't forget, a Heat Pump or Solar collector systems are available.
And as noted, the Prescriptive is certainly more restrictive, so if possible, use a designer who knows the state approved computer based performance programs...in the end, it will keep more dollars in the pocket of the responsible party.
 
Thanks for the replies. Not to familiar with the “prescriptive” route. Haha Joe and Ice you guys are hilarious I’m going to enjoy this forum. We can bring up all the other mandates happening around us right now but that’s not the topic here.
 
Joe.B said:
Interestingly I had this same question from someone who's building a new ADU behind their house and wants to go all electric as the trends are indicating. On-demand water heaters are popular right now, but the really only make sense for gas. Why? Because "the average electric tankless water heater needs at least 120 amps to operate" vs. a tank style which can operate off of 30-40 amps. The reason being with a tank it can gradually heat the water instead of all at once.
Click to expand...

So very true. Most need 3 separate 40A circuits in order to work properly. Whenever I see a renovation that converts to an electric tankless and the panel schedule shows a single 40A circuit, it gets flagged and 100% of the time they drop it because they need an larger service.
 
The CA Energy Code was intended to allow prescriptive measures similar to the Residential Code. What that means (for construction) is if you stay within the provisions of the code then you don't need an architect/engineer to stamp your design. Subchapter 8 of the Energy Code (150.1) offers two paths to compliance.

The performance standards (150.1(b)) approach says your building complies if "the energy consumption calculated...is no greater than the energy budget...using Commission-certified software..." This is where the "energy report" comes from, which 'round here folks call "title 24."

The prescriptive standards/component packages (150.1(c)) approach offers compliance by use of climate zone tables, prescriptive packages, and minimum standards. It's a thick read.

I'm still relatively new at this but I have never seen anybody use the prescriptive approach. It's easier to pay for the energy report. Literally the only person I've ever met who even knew what the prescriptive approach was is one of the local energy consultants who does the energy reports.
 
Joe.B said:
The CA Energy Code was intended to allow prescriptive measures similar to the Residential Code. What that means (for construction) is if you stay within the provisions of the code then you don't need an architect/engineer to stamp your design. Subchapter 8 of the Energy Code (150.1) offers two paths to compliance.

The performance standards (150.1(b)) approach says your building complies if "the energy consumption calculated...is no greater than the energy budget...using Commission-certified software..." This is where the "energy report" comes from, which 'round here folks call "title 24."

The prescriptive standards/component packages (150.1(c)) approach offers compliance by use of climate zone tables, prescriptive packages, and minimum standards. It's a thick read.

I'm still relatively new at this but I have never seen anybody use the prescriptive approach. It's easier to pay for the energy report. Literally the only person I've ever met who even knew what the prescriptive approach was is one of the local energy consultants who does the energy reports.
Click to expand...
Good Morning,
The read is very involved, but a prescriptive package does not allow an electric heater if gas is on or available to the property. That is where the Performance is needed. Hopefully, our contractors and designers taker this stuff serious because the California legislature sure does!!
I do see some waiving the Energy codes off, but only because they are not sure of the specific requirements. The provisions are again very involved, and with work being so crazy busy, just keeping up with the important safety provisions sometimes make these other provisions a passing thought! Good Luck to all.
 
Ed Cooke said:
The read is very involved, but a prescriptive package does not allow an electric heater if gas is on or available to the property.
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Looks to me like a heat pump style electric water heater is permissible 150.1 (c)(8)(A) iv or v, or am I missing something?
 
Joe.B said:
Looks to me like a heat pump style electric water heater is permissible 150.1 (c)(8)(A) iv or v, or am I missing something?
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Yes, that is correct. That is part of the prescriptive. I did not mention that here as I did on the reply from Friday @ 1:41pm. Sorry for the confusion. Some don't want to use this because the appliance is costly, but you are correct.
 
Ed Cooke said:
Yes, that is correct. That is part of the prescriptive. I did not mention that here as I did on the reply from Friday @ 1:41pm. Sorry for the confusion. Some don't want to use this because the appliance is costly, but you are correct.
Click to expand...
That's what I've heard. At least a grand more.

On the performance side of things I've had several residential projects that were submitted showing a regular tank style on the plans but in the energy report it calls out a heat-pump style, I assume because they couldn't meet the energy budget with the regular tank style electric. It gets noted as a correction and the plans get altered to show the heat pump style. Then they are into construction and they're asking me if they can install the cheaper kind and I have to say "yes, but you'll have to have the energy consultant redo the energy report and show that it works." Then the energy consultant tells them "yes, but you'll have to add another 1-2kw of solar." They end up having to pay for it one way or another.
 
Heat pump water heaters need to be in a space of at least 700 cubic feet volume or be ducted to a larger space so the air doesn't short cycle.
 
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