NFPA 13R System with 3/4" Domestic + Tank?

5/6/2025

I'm designing a 13R system. The building currently has a 3/4" domestic water service. The building is in a location that would make installing a new (larger) service a logistical nightmare.

Is it allowed to connect the 3/4" existing supply to a water storage tank (sized per system/domestic demand) in the basement, then build a residential riser from that?

If this is allowed, do I only take my calculations back to the storage tank?

Do you foresee other problems with this?

Thanks in advance.

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9 Comments

Pete H

5/6/2025 06:20:21 am

I'd do the tank with a small residential pump (something like the viking/econo residential pump, but listed for 13R. That pump is only for 13D systems) if I was that worried about the water supply.

In 13R any water tank shall be installed in accordance with NFPA 22 (NFPA 13R 9.5 2016 edition.) Additionally, check out the entire water supply chapter of 13R and the associated annex, it addresses tanks.

Karl

5/7/2025 09:39:45 am

Yes, it will require a 13R pump/tank system. The hydrant test shows good pressure and volume, but it's only a 3/4" line coming in for domestic, so the calcs have to include domestic demand.

The plumber's not sure if the 3/4" will satisfy 6 apts, so I was hoping he HAS to upsize, but I don't know if he's done any calculations. I think a pump/tank will be more cost effective than going through other properties, etc, for a new service.

Thanks for the input!

Jesse

5/6/2025 10:14:05 am

13R is the issue here. 13D is a lot more forgiving. There are a lot of pump / tank combos listed for 13D thata don't carry al isting for 13R. Any tank you install for a 13R design will need to meet NFPA 22 requirements

Karl

5/7/2025 09:34:19 am

Yes, the owner will need a 13R pump/tank system. Thanks for the input!

Colin Lusher link

5/6/2025 10:37:52 am

What type building is this? Single family dwelling? Because if it's 13D, you'd be fine, but if it truly is a multifamily/multi-story dwelling under 13R, that's not likely going to fly.

Karl

5/7/2025 09:30:11 am

So this was a small 2 story office bldg w/basement that is being converted to 6 apartments.

The bldg is "land locked" and only has an existing 3/4" water service, which I know won't cut it (4 hd calc). It is a 13R, so I'm convinced at this stage that the owner will need a pump/tank system (13R). I don't know if the 3/4" will be adequate for the domestic, I was kinda' hoping the plumber needed a bigger line so we could upsize it (2") for the sprinkler system.

I mentioned the bldg was land locked, it does have a driveway to it (100'+), but it's situated behind a gas station, so the shortest route would be through the gas station parking lot, which isn't going to happen.

I thought I'd post here because I always get great feedback from this forum. Thank you all for your input, and thanks to Joe Meyer for having this online presence. What a great resource!

Jack G

5/6/2025 12:22:05 pm

I m not sure what you are describing.
Do you mean a storage tank sized for both, and is a bladder tank like on a well?
Or a storage tank and you are going to install a 13 r pump and panel?
In either case, I would perform a flow test after the tank using a small meter and recording the pressures available.
Remember it’s a 4 head design.

Karl

5/7/2025 09:33:07 am

Thanks for the input, it will be 13R system, now I just have to tell the owner he's gotta' buy a 13R pump/tank system! & yes, it will be a 4 hd calc. Again, thanks for your input

Wes

5/7/2025 09:39:00 am

Just be careful; a Fire Pump for NFPA 13D does not need to meet NFPA 20.

A Fire Pump for NFPA 13R and NFPA 13 systems do need to meet NFPA 20 (per NFPA 13R-2025, Section 9.7.2). That's the full power requirements, supply, test header... everything that would be present in an NFPA 13 pump. Certainly could be smaller, but the requirements still go to NFPA 20.

The water supply has to be approved (see NFPA 13R-2025 Section 9.5). If it's a gravity tank, water storage tank at or below grade, or pressure tank, those still need to meet NFPA 22 just like we would do for an NFPA 13 system. So freeze protection, duration, low-level alarms... everything that would be needed for an NFPA 13 tank is also applicable to 13R because NFPA 22 is pulled in.

Not that it's insurmountable, just that it's an entirely different and more robust challenge than a non-listed NFPA 13D pump and small tank are.

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NFPA 13R System with 3/4" Domestic + Tank?

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