Tortured ROI Calculations: hot water insulation edition

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In general, I believe it's worth utilizing materials to reduce energy consumption - both are, of course, subsidized heavily in our economy, but materials are much easier to reuse, salvage, or recycle in the future. (Note my statement of utilizing materials, as opposed to using (up) energy.)

With this in mind, and an annoyance at how quickly the hot water turns cold if I step away from the dishes for just a few minutes, I decided to look into insulating my hot water pipes.

The US DoE's Energy Efficiency and Renewable Energy Office assured me of the quantitative benefits of insulating hot water pipes, though in a seemingly odd way:

Insulating your hot water pipes reduces heat loss and can raise water temperature 2ºF–4ºF hotter than uninsulated pipes can deliver, allowing for a lower water temperature setting. You also won't have to wait as long for hot water when you turn on a faucet or showerhead, which helps conserve water.

Armed thus with the knowledge that the project would actually have meaningful results, and the good luck of having the entire length of my hot water system accessible in a full-height basement, I set off for the hardware store. Note: make sure that, before you go, you measure both the linear quantity of hot water pipe that you have (it'll be a lot more than you probably expect!) and the diameters of hot water pipe - I have about 70 feet of pipe, with mixed 3/4" and 1/2". Pipe insulation comes in 6-foot-long lengths, slit along the length; installation requires only a knife to cut to length and duct tape or similar to ensure the insulation stays put.

Now for the fun part. Let's try to figure out when this project will pay off. I'm open to any suggestions for improving this estimate.


  1. Material costs were $15. Estimate 1.5 hours work for materials acquisition and installation, or another $15. [1]

  2. Savings is stated by EERE as "2 to 4 degrees" of temperature.
  3. Ambient/input water temperature is about 50 degrees, output temperature is about 120 degrees, so 70 degrees of heat is added.
  4. 2-4 degrees of efficiency improvement is 2.9%-5.7% of the 70 degrees of added heat. [2]
  5. I'll estimate we spend $16/month to run the water heater. [3]
  6. Percent savings * cost = $0.464-$0.912 savings on gas monthly at current rates.
  7. Total project cost / monthly savings = 33-65 months, or 3-5 years, to recoup the costs of the project in gas savings.


On the one hand, it might not seem worthwhile to undertake a project that will optimistically take 3 years to pay off, and then only have a return of $1 / month. This is especially true if you are renting. On the other hand, I'm pleasantly surprised to come up with any quantitative result at all, let alone the result that this will have a positive monetary return within so short a time as 3-5 years - if only everything I did on a Saturday afternoon could be counted as such a clear positive investment!

Additionally, taking into consideration the fact that I think my water heating bill is higher than the $16 used above, and that I expect energy prices to rise in the near future, this will probably pay off even faster than the 3-5 year estimate. Since I personally believe our current energy system to have high, but officially unacknowledged and thus unquantified, social costs, I see my investment as having an additional return in welfare for myself and my friends and family.

Therefore, I consider this project to be a clear win. $15 and an hour and a half of my Saturday that I'd otherwise no doubt have spent online with no real results [4] for a project that will provide positive benefits for the life of my hot water pipes. Not bad. And, if this write-up helps a few other people make the decision that it's a worthwhile project, I'll consider the time spent on it also worthwhile.


[1] Here I use the Ithaca Hours standard of $10/hour as the value of labor. Any economist you talk to will give you a different and conflicting reason why this is a bad way to estimate labor value. That's their problem.

[2] By this quantification, the lower your water heater is set, the higher a percentage savings you get. This is probably backwards, as heat loss will be fastest when the water temperature is higher. Oh well.

[3] Our gas bill for June-September averaged $32/month. This includes water heater and stove; no furnace use during that period. The stove is too old to have any sort of indication of gas usage marked on it, so I'm estimating half-and-half between the two. My guess is that the water heater uses more gas than the stove. As a check on this, the Missouri Extension states that water heating accounts for 15% of a household's annual energy bill. This would require a year's worth of energy bills to determine, but will come in higher than $16/mo.

[4] In the process of coming up with this quantification yesterday, I'm betting I spent at least an hour and a half on the garden path of agonizing over the comparative energy usage of my stove and water heater, leading into an attempt to figure out how fast a new water heater would pay off, despite the fact that my refrigerator, stove, and furnace are before that in the queue for replacement or tuning to address energy use, and we probably won't invest in a new water heater soon enough for today's efficiencies and prices to mean much of anything to me. So, yeah, I consider the project itself time well spent.

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Other stupid tricks

It's winter and my bathroom gets cold. Cinder block house + no insulation = cave-like temperatures year round. A few days ago I was in the shower and feeling chilly and pondering thermodynamics when I came to an epiphany: hot water going down the drain is energy that you're flushing into the sewer. If you plug the drain and let the tub fill with the hot shower water, your bathroom will be noticeably warmer when you step out of the shower. The smart thing to do is wait until it all comes down to room temperature and only then let it out of the house, using some kind of magic drain plug that monitors ambient temperature and water temperature.

Of course, there's nothing new in this world:

Also good: plastic vapor barrier over your shower to keep steam from escaping into the rest of the bathroom.

P.S. Why does my electric dryer vent outside in the winter?

P.P.S. All that wasted heat from your water lines is going to heat your house in the winter, so are you only seeing savings in the summer?

all good points...

1. What I worry about with using a tub full of shower water to heat/humidify the house is that our bathroom is conveniently located at the end of a narrow hallway that has a jog in the middle of it - so as to absolutely minimize the air transfer between the bathroom and the rest of the house. I think I'd have to install another vent fan transom-style above the bathroom door to have the effect be "heating and humidifying" rather than "molding". Also, the cat would totally drink the shower water.

2. My electric dryer does have all the dire warnings about venting it to outside, but, intuitively, I don't see why it would be a problem. It's not gas, so you're not producing CO or other problematic combustion byproducts, right? I do have easy access to the Building Official and Fire Marshall - maybe they can tell me whether using that lovely, warm, humid air to heat the house would be a Bad Idea.

3. The hot water lines are all in the unheated basement. (Well, unheated but for the leaky forced air ducts...) There is air exchange via the stairs, and warm air rises, so, yes, the heat's not technically being "wasted" in the winter. (And, back up to 1, supra, I suppose I'm actually making my house *less* heat efficient right now by more efficiently channeling heat to the drain. Hmmm...)

dire warnings

The dryer will will put heat, humidity, and lint into your house. To catch the lint lint you'll need a filter, which puts a bit of back pressure to the dryer. The humidity will go through your walls and ceilings and condense in the insulation unless your walls and ceiling have good vapor barriers on the warm side, or enough leakage to turn over your house air before it goes through the walls and ceilings. We had a filter on our dryer for a number of years, but the inconvenience of changing the vent between inside and outside twice a year was enough that i decided the humidity was indeed a problem. YMMV.

dire warmings

If you've got forced air and low humidity, the extra moisture could be considered a good thing. :)

hang drying laundry versus venting to the inside

A buddy of mine purchased a gadget several years ago that could be inserted 'inline' in the dryer hose, so that switching between exhausting to the outdoors versus the indoors was as simple as flipping a damper switch. What he discovered was that venting to the indoors made everything nice and warm and snuggly ... until the smoke alarm was triggered.

Even in an winter indoor environment where the indoor atmosphere could use some extra humidity, I wonder if plowing the moisture from a load of wet laundry into the air in less than an hour could still pose mold or consensation issues.

I've moved to almost exclusively hang drying, which releases the moisture over a period of about 24-hours. There's one floor-standing rack plus a very cool wall-mounted unit that I use. The wall-mounted unit is aces for saving space. The laundry levitator shown at the bottom of that catalog page I've linked to seems to require a very very high ceiling. Like the kind of ceiling you'd find in a barn. So I'm not sure I can really advocate for that one.

The big advantage to hang-drying comes when it's time to fold. Man, you can really fold that crispy stuff right on up. It's not all annoyingly soft and snuggly like it wants more to just roll up into a ball than fold properly.

Hang-drying and humidity

I don't think my household can handle hang-drying indoors in the winter; we'd end up with every article of clothing we own draped over everything in the house. (Hey, why fold it if you can just sort of graze your way into an outfit for the day?) In outdoor-line-drying weather, fear of rain/dew/theft keeps us honest about bringing it in.

I'm not too concerned about the quantity of moisture involved; our washer is very good at spinning water out of things, so I don't know if enough water would remain to get the house swampy. The kitchen and dining/living room is a large enough, open enough area that I think the humidity from a load of laundry would diffuse enough to not cause problems.

line dried

Your great grandparents had a clothes line that came inside to the basement for the winter and returned to the back yard in the spring. I like your idea of grazing for clothes in the morning. I'll have to see if that would fly around here. Not everybody likes line dried clothes: ECM complained about crunchy underpants.

"Not everybody likes line

"Not everybody likes line dried clothes: ECM complained about crunchy underpants."

Not everyone in my household likes lined dried clothes either. I accomodate by running their line dried clothes through a five-minute fluff (no-heat) in the drier with one of those little drier softener sheets.

As an occasional practitioner of the grazing-for-clothes method, my best advice is to remember that if you're doing it right, then you're starting from the point you get out of the shower and have dried off. That means it's worth planning which drying racks around the house you use for which articles of clothing. Rule of thumb: underwear goes closest to the bathroom. Unless you like prancing about the house neckid. And even if you do, bear in mind that not everyone in the household or on your block might share your enthusiasm for commando-style grazing.

Lint in the air

Besides venting a tremendous amount of mold creating humidity into your basement (which results in condensation and/or frost on windows, frames, wood, etc. in the winter) as well as creating the perfect conditions for wood rot, another reason to not vent your electric dryer into the basement is that lint particles get into the air everywhere, even with a filter.

In addition to creating higher than average dust in your basement, it can/will affect the performace of your furnace. I just had to have a service technician out this month to work on my 3 year old furnace (to the tune of $130). The house was consistently staying 1-2 degrees below the settings on the thermostat. Turns out that the sensors, igniters and burners were all fouled up with fine particles of dryer lint. The service tech said that this would continue to happen unless I walled off the furnace and/or dryer from the rest of the basement. I have an externally vented gas dryer and still have a problem with lint. I can only imagine what it would be like if you vented it internally.

I have seen some houses where an electric dryer was vented into the basement and it was not pretty. There was mold, wood rot and lint everywhere.

I definitely wouldn't vent

I definitely wouldn't vent directly to the basement - the dehumidifier only recently finished drying things out from the 5 inch floodwaters we had a while back - I've got an existing duct more or less directly above the dryer that I'd feed a vent hose up into. Lint would be the major concern, I think. (And laziness, since, y'know, it currently vents to the outside...)

I find it interesting that the most energetic discussion this page has seen since I turned comments back on is about dryer vents. I think I'm officially an old boring homeowner.

not so old

And Happy Birthday!

I wonder why a dryer vented outside would lint up the furnace. Does the dryer leak that much lint into the house? That's probably a leak in the duct which could be fixed with duct tape. Does the furnace draw outside air directly? From too close to the dryer vent? If so, then walling off either the dryer or the furnace won't work, but venting the dryer inside would.

If the house temperature is consistantly low then it's probably a thermostat problem. The furnace turns on and off as requested by the thermostat. The thermostat thinks it's cold, and turns on the furnace. The thermostat says Ok it's warm enough, and turns off the furnace. The furnace doesn't know the temperature at all. The thermostat is turning off too soon.

Most thermostats have a "heat anticipator" adjustment which can be set to match the particular furnace. This is a thing that says "if i tell the furnace to shut off, then it will turn off the flame, but it will continue pumping until the unit is cooled down, which takes "n" minutes, and will produce 1 or 2 more degrees, so i'll anticipate that and shut off now, a little ahead" If this heat anticipator is not adjusted properly then the house temp may be below or above the thermostat setting. The heat anticipator is inside the thermostat and is looks like a miniature thermostat lever inside the main thermostat. It usually is marked arcanely rather than with plain numbers, so it requires a Certified Furnace Repair Person to adjust. Sure it does. These days the CFRP googles the operator manual for the thermostat.

Having re-read all that, i wonder if there could be enough lint in the burners that it would change the burning temperature of the gas. Seems far-fetched. But if so, then perhaps a heat anticipator setting could be thrown off by a colder furnace operating temperature.

It's true, insulating pipes

It's true, insulating pipes can make all easier, you lower your energy consume and you also have heated water. Yet, insulating is just a small part of the process, you should also consider your appliances, new appliances can bring significant better differences. Sometimes appliance producers offer integrated solutions to a specific problem.

Dryer venting too close to Furnace Intake?

How close is too close?