Use a Well in an NFPA 13D Fire Sprinkler System?

4/26/2022

We have a house (single family home) that will require an NFPA 13D system, but it is not going to be connected to city water.

There is a well onsite. The well completion report does not provide a pressure or flow output.

Can the well be used as part of the hydraulic calculations? What data would be necessary to incorporate it?

If not, I'm assuming that both a pump and tank would be needed here for the 13D system?

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5 Comments

Alex

4/26/2022 06:45:08 am

Hi,

NPFA 13D (2013) 6.2 states that a "well with a pump of sufficient capacity and pressure to meet the sprinkler demand" shall be considered acceptable as an available water supply.

You will need to ensure that the well pump and holding tank can satisfy a 10 minute water demand rate (6.1.2) or 7 minutes if you fall under the provisions listed in 6.1.3.

You will need the following:
- holding tank size
- available pressure
- determine your demand duration
- determine your demand flow
- determine your required pressure

NPFA wrote about this back in 2019 as well: https://www.nfpa.org/news-and-research/publications-and-media/blogs-landing-page/fire-sprinkler-initiative/blog-posts/2010/02/19/nfpa-13d-fire-sprinkler-systems-on-well-water

Thanks,
Alex

Jesse

4/26/2022 08:10:37 am

We have done a handful of these with similar issues. Alex is correct.

The one that I did with best results had two pumps. A well pump pumping from the well into a storage tank with about 500-g capacity, and then a pump from the storage tank to the domestic system. The tank more or less functioned the same way a break-tank or surge tank would work in that the well pump was never considered in the calcs. In our case, with a 500-g tank clearly the 10 minute duration wasn't an issue even without considering refill rate. As I recall, our AS demand was in the area of 30-GPM.

Joe

4/26/2022 10:02:26 am

We have installed many 13D projects with private well pumps. A large majority of private well pumps will not produce the required flow unless the well pump is a variable speed pump.
We typically end up installing an independent 13D Pump & Tank System like the Talco Home Hydrant for example.
We design for a 16'x16' Spacing with a K4.9 requiring 13 GPM for two sprinklers, so 26 GPM would be required.
If you install the 13D pump & tank system, make sure the plumber provides a 3/4" auto fill water supply line with shut-off valve above the tank. The autofill will provide additional water for fire protection.

Dave

4/26/2022 10:25:53 am

Like Joe above, I've designed many 13D's supplied by a private well, if it could provide the supply and duration. Sometimes keeping sprinkler spacing at a minimum, once in a while get lucky and not have a compartment with more than one sprinkler. Often had to upgrade the well pump itself, or catch it early if a new well. But I prefer the pre-packaged 13D units if it's in the budget and there's space for it. As you know often the uninformed owner is already angry at having to install a system at all.
13D was not our bread and butter, that alone wouldn't keep our lights on, but we did them to provide a complete service.

Scott McBride

4/26/2022 10:59:12 am

As an AHJ, all of the others are on the mark. I also emplore you to have a discussion with your local AHJ and find out what specific requirements that they have regarding rural supplied 13D systems.

Does the well pump feed directly in to the tank or is it connected to the domestic water supply and the tank. If so you may be required to install a backflow preventer.

You can also reduce the size of the tank if you have limited space for the tank and the data for the well pump is known, but if not I would recommend sizing the tank for the required flow from the calcs times 7 or 10 minutes as required. As mentioned above though you must account for refill time if you are reducing tank size.

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Use a Well in an NFPA 13D Fire Sprinkler System?

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