What's the best way to insulate copper pipes?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by stark, Jul 26, 2009.

  1. stark

    stark New Member

    New Jersey
    In the winter I notice that I run out of hot water in the shower much sooner than I do in the summer (I enjoy long, hot showers). I attribute this to the exposed copper water pipes in my basement. The basement does get considerably colder in the winter because I live on a hill and it's only partially underground. I recently learned that I can insulate these copper pipes, but I'm not sure which product I should go with. At Lowes I see a variety of choices -- rubber insulation tubes, foam insulation tubes, pipe wrap foil, and fiberglass pipe wrap. Do the professionals among you have a preference for pipe insulation? Is one better and/or easier to use than the others?

    Thanks in advance! :)
  2. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    At the supply houses, we get the foam insulation with self stick.
    The foam is split, you slide it over the pipe, and pull out the clear plastic strips covering the adhesive.
    Then you can push it together.

    If you don't have that, then the ties may be a good idea.

    The home center insulation doesn't have those features.
    Their customers only worry about cost.

    Plumbers worry about time, and not having to go back.
    Last edited: Jan 10, 2010
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    It's much more likely that the cold incoming water is the culprit that is shortening your long hot showers in the winter than the insulation. That is not to say that insulation isn't a good idea, but don't expect much in the duration of your shower.

    One way to make the WH appear bigger is to raise the temperature. This can be dangerous, but that can be resolved if you add a tempering valve. This essentially mixes cold water with the hot (if required, i.e., it is too hot) to limit the outlet temperature.
  4. Dana

    Dana In the trades


    Another way to make the water heater to appear bigger (at least for showers, but not tub-fills) is to install a drainwater heat recovery heat exchanger on the main shower. By preheating the incoming hot & cold water with the waste heat of the shower-water flowing down the drain, literally half of the heat is recovered directly, doubling the continuous flow capacity of the system. This is WAY more extended capacity than bumping the storage temp higher and using a tempering valve, and it doesn't increase standby losses the way higher storage temps do.

    They're not cheap ($500-700 for a decent-sized one), yet they can be a reasonable DIY project. (Easier for the DIY crowd if you have PVC drains though- if you're breaking into 100 year old cast iron yo may want to higher a pro.)

    The two biggest manufacturers of them are GFX and PowerPipe. See:







    Independent verification & performance testing

    In places with expensive utilities (electric hot water @ 20 cents/kwh) the payback in utility savings alone is well worth it (even when installed at professional rates.) It can turn your 32kbtu/h gas fired tank hot water heater into a continuous flow system during the warmer-water months, if not the dead of winter.

    The best way to insulate your pipes is to air-seal, vapor seal and insulate the basement foundation, sill & band joist, turning it into conditioned spaces, but that's a whole 'nuther project with a very different budget, eh?

    But if it's extended showering capacity you're after (without resorting to a more expensive and higher-maintenance on-demand tankless heater), drainwater heat recovery is a great way to go, and it pays for itself (eventually) everywhere. Get the biggest one that actually fits. If you don't have the headroom for a 60-incher, go fatter. The heat transfer efficiency is all about surface area- a 48" x 4-incher has about as much heat transfer surface area as a 60" x 3 incher, with similar performance.

    But note- since it's a counterflow heat exchanger, it doesn't really work for tub filling, since the drainwater isn't flowing at the same time that the water is coming in. (There's some heat recovered in tub fills/drains & other batch draws, but it's in low single-digit percentages vs. 50-70% during showers for the bigger units.)
  5. jastori

    jastori New Member

    You wrote:

    As you use hot water from the tank, cold water is continuously entering. Your hot water heater is adding heat to the water in the tank at the same time. However, your hot water heater cannot keep-up, and the average temperature of the water in the tank will keep dropping as the ratio of old hot water to new cold water keeps dropping.

    A 15-20 degree difference in the incoming cold water temperature between summer and winter will have a large impact on how long of a shower you can take.
  6. Dana

    Dana In the trades

    ...as will a 30-35F RISE in incoming cold water if you're using a drainwater heat recovery system as pre-heat. It's not just the mixing in the tank- it's the cold water you're mixing at the shower as well.

    If you pre-heat both hot & cold with drainwater heat recovery your flow from the tank is lower because you're mixing in more of the cold water stream which is now ~75F, not 40F, the water entering the tank is already warmer, only needs ~half as many BTUs to come up to temp, and the tank-mixed water is warmer since it's mixing with ~75F water, not ~40F water, etc. It all adds up to longer showers with a more graceful tapering when you're beyond the capacity of burner + recovered heat, with a quicker recovery on the tank when you DO run it down to less than showering temps.

    Seriously- drainwater heat recovery is equivalent to adding 25-30KBTU/hour of burner while taking a shower (and the best part is the fuel for that "burner" is free!) That roughly doubles the burner of a typical tank heater, putting the combined capacity in the range of mid to large-sized point-of-use tankless heaters that Europeans shower with every day(!).

    If the water heater is located anywhere near the main house drain or the primary shower drain, this is THE solution. Even if it's 5-10x more expensive than adding massive insulating the pipes & tank, it's 100-1000x more effective for extending showers. It's also on the order of 10x more effective than just boosting the tank temp to 160-180F and installing a tempering valve for scald-control (which would buy you something, but it still won't be endless-shower time, and your standby losses would roughly double.)

    Of course, if you never run out of hot water your fuel bills will go up 'cuz you'll never get out of the shower! :) (This is a known phenomenon with tankless HW heaters- people can and do take longer showers knowing they won't get screamed at by the next in line for hoggin' all the hot water, and the fuel savings aren't always as-anticipated.)
  7. con8iv

    con8iv New Member

    Does this only work well if you have a basement. I, too, am repiping a 1950 house, but it is a pier and beam, one-story, and we are moving the HW heater into the garage.
    Last edited: Jul 28, 2009
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    A heat exchanger needs some length to enable efficient energy transfer. Water going down a vertical drain tends to cling to the sides and if the heat exchanger is there, it can do its job. It isn't anywhere near as efficient on the horizontal, since you only have flow in a small surface.
  9. Dana

    Dana In the trades

    It's not the length per-se, it's the total surface area.

    But yes, they do need to be installed vertically- horizontally the percentage of the surface area of the pipe in contact with the water drops to under 25%, with a corresponding loss of heat-transfer efficiency. A 3 footer with a 4 inch drain can do remarkably well- on the order of 45-50% of the heat is recovered at shower flow rates. Even 20" x 4" heat exchangers return a third or so, and it can often fit in a crawlspace.

    See figure 2a (lower left) on this document for the performance of 4" bores of various lengths & flows:


    Those curves are modeled on decade old GFX designs too- they're likely better today. PowerPipe's design seems in a couple of ways inherently better than the current GFX, and will likely out perform the GFX stuff slightly, but all manufacturers' designs are in a constant state of flux, squeaking out a bit more with each iterative release- can't say for sure year to year who will be a nose & a hair ahead. Canadian testers believe the squareness of the cross section of the potable water coil is the key distinction that makes for better heat transfer performance, since the squarer it is, the greater percentage of contact with the copper drain core, and they've ALL gotten squarer since 20 years ago.

    I guess there's not much you can do about showers in basements, slab-on grade first-floors, etc., unless you want to dig a pit to accommodate. But it doesn't take much of a pit to install a 2-footer (if anybody still makes 'em that small- maybe Retherm? The all seem to have 30-36" versions.)

    Any installation will work somewhat better if you insulate it with an R2-R8 wrap afterward, particularly if it's in an unconditioned crawlspace or something. (A double layer of bubble pack held in place with zip ties would do for most.)

    Clearly it helps if the hot water heater is already located next to the main drain exiting the house though. A lot of issues can make retrofits less than ideal, but for some it's clearly the best, cheapest, most-effective solution for endless showers short of going tankless (for a lot more money.)

    For greenies it's a way of adding another 10-12% to their solar fraction, or another 0.1-0.12 to their as-used EF of any fossil fired or electric hot water heater, etc. (There are plenty of LESS cost effective purchased efficiency options out there than a drainwater heat recovery heat exchanger.)

    OTOH is could be just viewed as an enabler of wasting more water (if not more energy) with endless showers. :)
  10. Gordan

    Gordan New Member

    SE PA
    I don't know, Dominic. I've seen Dana weigh in on a number of issues on a number of occasions, always in a helpful manner. I can't say the same of you - you appear to have just joined. In my eyes, he certainly has vastly more credibility of the two of you. But I guess if you say it, it must be true, so...
Similar Threads: What's best
Forum Title Date
Plumbing Forum, Professional & DIY Advice Garbage disposal - what's the very best? Nov 27, 2011
Plumbing Forum, Professional & DIY Advice What's the best washer shut-off value to buy? Dec 16, 2010
Plumbing Forum, Professional & DIY Advice What's the best way to "start up" a newly pumped septic tank? Dec 30, 2007
Plumbing Forum, Professional & DIY Advice New house planned: What's the best plumbing designs in the world? Sep 5, 2007
Plumbing Forum, Professional & DIY Advice What's the best valve for "shut-off" Sep 29, 2006

Share This Page