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Supply sizing

islanderislander Posts: 4Member
edited June 2018 in Plumbing
Hey there.

Need some help from your collective brains. A friend with a master license in heating recommended this forum.

Mum-in-law has Parkinson's and Pop-in-law has cancer, so trying to build for all of us to caretake as things progress. All this on a shoestring, so bought an old excavator and old dump truck, rented a dozer and we'll see how far we get!

New build, coming off 6" municipal water supply at 80 PSI. Elevation change of 25' to house 500' from line. From there, there will be a garage with 2 apartments located another 200' away and another 15' elevation change including the second story. So we have the house, and then another building 200' away with a one level apartment for the in-laws (let's call that the apartment), and a small studio over the garage for my parents (let's call that the studio).

Total of 6 baths, 3 kitchens, 2 laundries, 4 hose bibbs for a total of 72 fixture units for the house, apartment, and studio.

The local town guys who maintain and operate the system had not heard of fixture units, so did not know how to compute pipe size for the supply. They did run it by some engineers briefly a few months ago, but at that time the house was 600' away with the apartment attached (had to move house site this week due to ledge/trees, and now the apartment and studio are in a separate building). Back this winter I found some chart on the internet I can't find again that showed me that with the pressure loss in line size vs. the amount of fixture units, that I was just (but definitely) into 2" size for the supply line from the municipal main. Now, we've moved the house 100' closer, and separated the buildings, so now it is 500' with 200' farther. The town guys and I are supposed to do a wet tap this Friday, and they are asking what size water meter I will be using in the near future (1" or 1 1/2" is supplied by the town, but they say that a 2" would be my cost). There will be one meter for both buildings.

Here's the three-part question: What size supply, water meter, and main inside the buildings is necessary?

Prices for corp, curb stops etc goes from $90 for 1" to $400 for 2" and everything else goes up too - blue poly, cost of wet tap, etc etc.

Wish I could find that little chart I used months ago when I first looked at this.
Here is a link to a somewhat helpful webpage: - Sizing Domestic Water Pipes.pdf

Do I still have to do a 2" supply? Or now that the distance to the house is reduced from 6 to 500' can I do 1 1/2"?
What size supply do I need to run to the apartment and studio (2 kitchens, 2 1/2 baths, 2 hose bibs, 2 washers)?

According to the link above, maybe 1 1/2" is enough for both and then run a 1" main inside?

Another possibility: Do 2" and reduce outside the house to 1 1/2" at a curb stop, enter the building and go through an. 1 1/2" meter, and then run 1" after the meter to the apartment/studio?

Don't want to over-engineer this, but also don't want to spend thousands unnecessarily. Especially not knowing how to account for demand, since everything won't be on at the same time (or do fixture units already account for that?).
Just scary that I was told that a 12 story building being built in a nearby city was being fed off a 2" line.....??

THANKS in advance for any of your help!


  • Jamie HallJamie Hall Posts: 10,279Member
    Your fixture units calculation is way off. Six bathroom groups is about 22 fixture units. The three kitchens are 7.5. The two laundries are 5. The house bibbs are a total of 10 -- 44.5 call it 45 fixture units. You have to use the group figures, not the individual ones -- then it takes it into account that it's unlikely that you will be using everything at once. Now the maximum elevation (I assume the elevation changes are up?) is 40 feet, which is about 20 psi. Roughly. So you're looking at 60 psi static at the highest point.


    An inch and a half meter and inch and a half distribution line should do the job.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ScottSecorScottSecor Posts: 213Member
    We do very little with DFU calculations, however we do a lot of work in multifamily buildings. Based on the load, distance and elevation above the main I agree with 1.5" pipe and meter, should be more than enough. Maybe you could get away with 1.25" pipe, but is it really worth risking it? Only problem I could possibly see is if there were five or six people per apartment, all using the water at the same time which sounds very unlikely.
  • hot_rodhot_rod Posts: 11,259Member
    what type of pipe or tube will you be running? Check the pressure drop tables if you are using HDPE or PP the id may be smaller than copper, for example

    The biggest unknown is how many fixtures will be or could be running at the same time. Do the add monthly fees for a large meter set?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • islanderislander Posts: 4Member
    edited June 2018
    Thank you very much! Yes, you are correct, the elevation changes are up. Question: do you have a link to somewhere that explains group vs individual fixture counts? Makes sense to me. Also, what would you recommend for main line inside each building after the 1 1/2" meter? (Please also see second half of comment to Scott below)

    Thanks. Totally agree that leaving a little headroom is wise. My only concern is that most tables seem to end at 500', and we will have that to the house and then an additional 200' run to the apartment and studio. I'd hate to have pressure/capacity loss because of that extra footage.

    The only online document I found that shows past 500' is this one:
    According to it, I'd need 1 1/2" for everything, including inside the buildings for a main (building supply) for a static pressure of 60 and above would be 51 fixture units, and as Jamie says above, it appears that grouping would be 45. However, for 46-60 psi it is only 38 fixture units, below both the original estimate of 72 and Jamie's 45, which then shows doing an 1 1/2" street supply and a 2" building supply. Sigh.

    It is ADS CTS. Here is the link:
    No, I don't believe there are any fees. Only if multiple meters are used, it seems.
  • Jamie HallJamie Hall Posts: 10,279Member
    No, I really don't know of a reference for why supply fixture units are reduced the way they are for groups -- except from experience. Long experience. The fixture units are set relating to the gallons per minute of the fixture in question, but the thinking is that in groups its highly unlikely that everything will be used at once. Therefore the group gets a lower rating than the sum of the fixtures. Seems to work...

    There are exceptions, of course -- and they were spelled out pretty well in the old National Plumbing Code, but you'd have to find a copy from the early '70s or before.

    You would treat the line up to the other building -- that 200 foot line -- as a separate main, not add it to the 500 feet. Starting at the main building. I'd probably stay with the inch and a half, just for the margin as @ScottSecor suggested, and hook it in in the main building to the inch and a half coming from the street. Within the buildings fixture units are used to size the lines in much the same way.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hot_rodhot_rod Posts: 11,259Member
    it really comes down to how your family uses water. A hotel design for example has large loads for about 2 hours in the AM and 3 or so hours in the PM. Piping needs to be sized to accommodate all that load occurring at peak hours, both piping and DHW capacity.

    Generally residences have a completely different use pattern and rarely would every shower, dishwasher and washer be running at the same time.

    IF the pressure dropped below 60 psi for brief periods, would that be a problem.

    Plenty of homes with 1/2 and 3/4 water mains. If pressure becomes a problem, or the mains are low pressure, a simple ECM variable speed booster pump is added. The only time we installed 2" on residences was for fire protection systems.

    Residential boosters are a huge market out west in water shortage areas where main line pressure drops at peak hours.

    With the info you have supplied, 1-1/2 is plenty, 1-1/4 would work for most families, if they even offer 1-1/4 meter sets?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • islanderislander Posts: 4Member
    Thank you gents! Fantastic resource here. Appreciate it!! Now to go try to change the town's mind....
  • islanderislander Posts: 4Member
    Talked to the town. They agreed to the 1 1/2". But now they want to step the meter down to 1". Thoughts?? I'm still planning on running 1 1/2" to the apartment/garage for the 200' run. I'm also thinking 1" supply for inside each building would be definitely adequate. Could I ask for your thoughts, men?
  • hot_rodhot_rod Posts: 11,259Member
    yeah, that seemed cheap for a 1-1/2 meter set, especially if it involved a back flow device. $1500 was the going rate in my area for a set that size, typically commercial jobs. I think you’ll find a smaller set with a booster ends up being less $$, if in fact you need that much game

    Look at the Grundfos Scalia (sp) booster packs if you find you need more home or pressure.

    I’d still run the 1-1/2 lateral in the plastic you mentioned, that is your big pressure drop.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Jamie HallJamie Hall Posts: 10,279Member
    Try it without the booster first; it's possible that the pressure drop through the meter set will be tolerable.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • heatheadheathead Posts: 84Member
    When I wanted my town to install a pressure regulator because of high pressure at times, I learned I had 5/8 meter size, but 1 inch supply lines. I guess just small reduction less than 1 foot. I would have never though the meter was 5/8.
  • ratioratio Posts: 1,930Member
    Around here, 5/8" meter setting, 3/4" supply line is the residential size, IIRC you have to buy anything larger. Seems to work just fine, but then I'm not what I consider high demand.
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