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Community and Q&A

Pipe insulation mediocrity

Nick Welch | Posted in Energy Efficiency and Durability on

Is there any data on how much heat loss occurs in pipes and what kind of payback there is for better insulated pipes? The foam stuff commonly available has a very mediocre R-value that rivals windows, and I find myself pondering better solutions. Am I veering into crackpot territory, fretting over something that isn’t a significant issue? Or have I stumbled upon a genuine blind spot in energy efficiency practices?

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    As I wrote in my article, All About Water Heaters, "Pipe insulation has only limited value, since it helps keep water hot for only 30 minutes or so. Nevertheless, insulated pipes are preferable to uninsulated pipes."

    If you are installing pipe insulation, the most critical pipes are the ones closest to the water heater. Many building codes now mandate the use of pipe insulation for all hot water pipes.

    Designing an efficient piping layout matters much more than pipe insulation. The best thing you can do is to locate your bathroom(s) close to your kitchen, and to install your water heater as close as possible to these areas. Use small-diameter hot water pipes, not large-diameter pipes, and keep the runs very short.

  2. Aaron Gatzke | | #2

    Is it acceptable to mix a 3/8ths hot water and a 1/2 inch cold water run to a fixture?
    And which fixtures can you change the pipe diameters with? I would imagine a faucet would be alright but what about a shower? A tub has to be filled quickly so I guess you would use the half inch.
    Some appliances like dishwashers and washing machines have built-in water heaters but what if they don't? Would it make any difference?

  3. Aj Builder, Upstate NY Zone 6a | | #3

    Compared to all other costs in one's life hot water is about the lowest bill. Taxes, mortgages and repair renovation costs are anyones main costs to reduce if one really wants to chop away at costs. Insulating your hot water lines may be worth a twenty dollar bill more or less per year. Now insulating the cold lines is worth doing if the cold lines are dripping condensation water. Last install I did insulate twenty feet of hot and cold while changing out a hot water tank. There is a benefit but not really a monetary one.

    The other point never mentioned is that during the six month heating season much waste heat from water lines and ducts and TVs and computers and outlawed incandescent bulbs is helping heat a home, so is not wasted.

    Buy a home that costs less, has lower taxes, has a mini split for heat and a few solar panels, lots of cellulose blown in the attic, R 5 windows, southern exposure, with just a bike or walk to work... Then you might just reduce your annual costs enough to notice.


  4. Nick Welch | | #4

    AJ, water heating is often the #2 single energy use in a home, behind heating/cooling. In a very efficient home, it can actually be the #1 energy use.

    If what Martin is saying is true, then even with copious pipe insulation, enough heat will have left the pipe in 30 minutes to make it no longer considered hot. That would seem to be the reason why little attention is focused on insulating the pipes better -- who cares how long you can keep that last degree of heat in there, if it's tepid anyway. That makes sense. But so little is said about the issue that I'm not completely convinced yet.

  5. User avatar
    Dana Dorsett | | #5

    IRC 2012 calls out R3 min for all hot water distribution plumbing. Most of the crummy 3/8" wall stuff sold in box-stores runs R2, but there are many vendors of 5/8"+ walled R4-R5 goods available through plumbing supply houses, Graingers, etc.

    Ultimately is isn't the long-term preservation of the water temperature in the pipes that make the big difference, but rather the extension of the time to cool, leading to less tepid-water dumped down the drains on successive draws. The heat truly lost during the heating season is the volumes of tepid 80-90F water going down the drain (water that came into the house at 40F), not the abandoned heat in the plumbing that is passively heating the conditioned space as it cools. At R4 there's still "payback", at R6, maybe not for most people- depends on your energy costs. This is all fairly elegantly layed out in this piece of "science in the home":

  6. Aj Builder, Upstate NY Zone 6a | | #6

    Nuts Dana and Nick.

    Nick do a spreadsheet of your own annual costs.

    Property Taxes
    Then somewhere hot water... and then just a fraction of that small bill would change from insulating pipes. And in the winter the heat lost in the water displaces heat one needs to purchase to heat the living space of the home. We are talking pennies and dollars not Benjamins.

    Dana... you are smart guy.... insulating pipes at my home is not going to save a Benjamin for me, no way. But would be glad to have you run the numbers and include the fact that most of my water heat loss stays in my home HEATING my home which needs heat for 8 months a year. And by the way my PVC drain pipe in my cellar is quite long. I have checked the outgoing water temperature and I am even through PVC recovering heat energy from my water waste into my home heat needs.


  7. User avatar
    Dana Dorsett | | #7

    AJ: The heat going down the drain as a volume tepid water doesn't heat your house, and is more half the heat energy that went into it in a 6A NY climate. Pipe insulation reduces the volume of tepid water dumped.

    On a lifecycle cost basis we're talking Benjamins even in cheap energy markets. And it's cheap stuff, with a very good IRR as a DIY project.

    Sure, it's not the size of investment that will fun your retirement, but it's not just stuffing a Jackson or two down a rat hole never to be seen again. The original question was about payback, not the size of the investment. Yes, there IS payback at R4. (Don't take me to task for merely answering the question, eh? )

    But that energy waste is a miniscule fraction of the total energy use of an IRC 2009 code-min house.

    IRC 2012 code-min house come with R3 on most of the distribution plumbing, as noted here:

    N1103.4.2 (R403.4.2) Hot water pipe insulation (Prescriptive).
    Insulation for hot water pipe with a minimum thermal resistance (R-value) of R-3 shall be applied to the following:

    1. Piping larger than 3/4-inch nominal diameter.

    2. Piping serving more than one dwelling unit.

    3. Piping from the water heater to kitchen outlets.

    4. Piping located outside the conditioned space.

    5. Piping from the water heater to a distribution manifold.

    6. Piping located under a floor slab.

    7. Buried piping.

    8. Supply and return piping in recirculation systems other than demand recirculation systems.

    9. Piping with run lengths greater than the maximum run lengths for the nominal pipe diameter given in Table N1103.4.2.

    All remaining piping shall be insulated to at least R-3 or meet the run length requirements of Table N1103.4.2.

    TABLE N1103.4.2 (R403.4.2) MAXIMUM RUN LENGTH (feet)a

    Nominal pipe diameter of largest diameter pipe in the run (inch) 3/8 1/2 3/4 > 3/4
    Maximum run length 30 20 10 5

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
    a. Total length of all piping from the distribution manifold or the recirculation loop to a point of use.

  8. Aj Builder, Upstate NY Zone 6a | | #8

    $500 to heat water annually. NO WAY am I going to save $100 annually via all my pipes insulated to even R 50 Dana.

    Insulating pipes has value to stop cold line dripping. It has value to keep water warm enough for a second drawing of water done timely from the last use.

    I have made some changes of late that do make a difference. I use cold water way more often than I use to. I wash my hands in cold water, rinse dishes in cold water etc. This change makes insulating pipes a non issue.

    And as to where the heat goes from my water pipes, it goes into my home. That is a good thing year round for me as my basement needs some heat 12 months a year.

    As to my drain water, it cools down to close to it's incoming temperature in my home heating my home which needs the heat. My drain captures this heat exactly like the systems that capture it back into the incoming water. The only difference is where the heat lands, in the water or in the home. Both need heat. Both cost me money to heat. The savings happens either way.

    All the waste heat coming from my water heater and water piping is heating my home especially my cold basement. All that waste heat is being used.

  9. User avatar
    Dana Dorsett | | #9

    AJ- where does that $500 year number come from? Is that your annual water heating costs?

    And if those are your actual costs, why would you need $100/year savings to think it's worth spending $40-50 for R4 pipe insulation sufficient to do your whole place? That implies you demand an IRR of more than 200% before you feel it's rational(?)! Even loan sharks and payday lenders settle for a lot less than that, credit card companies are thrilled to see 20%.

    I'd like to see your drainwater heat recovery system documented. The best anybody else seems to be able to do is a bit above room-temperature (with the exception of continuous flow draws like showers, with counterflow drainwater heat exchangers that might recovery 50% of the heat, delivering water below room temp to the drain.) Assuming you're pulling 40F water in, storing the greywater in a basement tempering tank before letting it run down the drain at 65F is still more than 500 BTU/gallon. Even water-sippers who have indoor plumbing will use something on the order of 50 gallons/day (half of which is hot water). That's 25,000BTU / day down the drain, half of which is hot water, so with the reduced tepid-water dump you get with pipe insulate you-personally might save something like 1000-5000 BTU/day is saved with the pipe insulation for water-mizers, 10,000 BTU/day for the average folks.

    If you're heating your house & hot water with condensing propane, that 1000-5000 BTU/day number adds up to about 4-20 gallons of propane a year, which might be closing in on your $100/year number at the high side, but might only be $20. (Oh gee, only a 50% IRR? If that's all it's worth I'm taking that pair o' Jacksons and stuffing it in the mattress!)

    If you're not storing all of your greywater in at tempering tank and the water leaves the house at a higher temp, your losses are even higher.

    You state:

    "Insulating pipes has value to stop cold line dripping. It has value to keep water warm enough for a second drawing of water done timely from the last use."

    EXACTLY. Every time you purge the 85F water down the drain to get water of sufficient temp, you're throwing away something on the order of 200-1200 BTU, depending on the length & diameter of the run, unless you temper it in that 500 gallon greywater treatment & tempering tank heat exchanger you have in your basement to cut your losses to half that. (Are you pre-heating the incoming potable with a ball of PEX as the heat exchanger in a tub full of greywater, or what?)

  10. Aj Builder, Upstate NY Zone 6a | | #10

    Cellar in winter is below 40 degrees. I have almost 100 feet of drain pipe in the cold cellar. I have checked my drain water temperature and it is very close to PVC pipe temperature.

    And this is another part you fail to understand. Insulating my pipes means I will have to add heat to my cellar via my furnace.

    You just aren't understanding this at all Dana. I am USING the heat my water heater and my uninsulated plumbing is losing to heat my cold cellar and keep all just above freezing temperature.


  11. User avatar
    Dana Dorsett | | #11

    "You just aren't understanding this at all Dana."

    That's right- if you're dribbling out one or two pixels of the details your personal picture per post I'll only fully understand YOUR situation in about 5 years! :-)

    But if your basement is truly 40F all winter it's not an insulated tight basement that meets IRC 2009 code-min, and you're personal situation is a 3-sigma outlier regarding potential benefits from insulated hot water distribution plumbing. What's arguably best in your situation doesn't really apply to the other 99.7%.

    Most basements in the north east average winter temps well above 50F- even uninsulated basements, and insulated basements will usually average above 60F if the hot water & space heating appliances are located there (as they usually are.)

  12. Keith H | | #12

    One thing to consider is that there is a bell curve of skills using this site. There are full on builders (like yourself I assume), hardcore DIYers (I put myself in this box), and folks who are going to pay other people to do 95% of their home maintenance but are curious whether something is worth buying or doing. There are not a lot of things that last set can do to save energy but insulate their pipes in their crawlspace is one of them. Same story for things like caulk, canned foaming, etc. If I pay someone $35/hr to do these tasks, the payoff is probably never. But if its one energy efficiency item I can do myself on the weekend, why not? It pays off eventually and may make my home a little more comfortable.

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