I'm just wondering, wouldn't it be more energy (cost) efficient for hot water to be heated on-demand, possibly through a propane heater system? I'm living in a small trailer with a tiny water tank that limits showers to about 10 minutes and takes forever to reheat.

I'm just wondering if anything like this is on the market, and if not how hard would it be to design?

Is such a heating system better than a traditional tank?

Yeah, they're already out there. Called tankless water heaters.

edit: How Stuff Works: Tankless water heater edition (http://home.howstuffworks.com/tankless-water-heater.htm)

PirateJoe is right. They're also called instantaneous water heaters. They aren't great for large installations.

As said above, Tankless water heaters are the latest big thing in Europe. They are designed for small space homes, such as a trailer or a small apartment or home. They can be mounted on a wall and are only about 3 feet tall 2 feet wide and stick out about a foot. The tankless waterheaters are used on demand. They will switch between hydronic heating and domestic hot water heating on demand. They have a priority for domestic hot water over hydronic heating.

Taco makes one called the Munchkin.

Before you get too excited these are kinda pricey. They run at the cheapest $10,000 to $12,000 for just the heater. A full install will run at the least $16,000.

Edit: They are extremely efficient (97% ish if i remember correctly) your hot water heater is probably at the most 80% efficient.

^^^I'd love to see a source cited that backs up those figures man, or anything like them.

Instantaneous water heaters are generally three-phase, that's the problem.

I actually went and dragged out an old electrical textbook to get some info for you.

"Because of the high demand on the supply system and the necessity for a three-phase supply, most energy distributors discourage the installation of 3-phase instantaneous water heaters. Instead, the encourage the installation of off-peak hot-water systems, which make fewer demands on the supply system.

A 16.5kW (23A/phase) instantaneous water heater is capable of supplying approximately 6545L/day, but the heater cannot efficiently supply more than one tap at a time and will switch off if the flow is drastically reduced."
Electrical Wiring Practice. Volume 2. 6th edition.

^^^I'd love to see a source cited that backs up those figures man, or anything like them.

Instantaneous water heaters are generally three-phase, that's the problem.

I actually went and dragged out an old electrical textbook to get some info for you.

"Because of the high demand on the supply system and the necessity for a three-phase supply, most energy distributors discourage the installation of 3-phase instantaneous water heaters. Instead, the encourage the installation of off-peak hot-water systems, which make fewer demands on the supply system.

A 16.5kW (23A/phase) instantaneous water heater is capable of supplying approximately 6545L/day, but the heater cannot efficiently supply more than one tap at a time and will switch off if the flow is drastically reduced."
Electrical Wiring Practice. Volume 2. 6th edition.

Here is a source for you, the efficiencies are on the first page. Obviously with an output of only 80,000 btus you would not want to put these inside your mansion in Alaska. I have some munchkin product manuals i could scan for you if you don't believe me. They are a new product so your old electrical textbooks would not have them. I am getting a HVAC engineering degree, so I have access to alot of material on things like this.

http://www.2hsc.com/pricing/pdfs/hsc_pricing_htp.pdf

Here is another source for you:
http://www.jupiterheating.com/munchkin-boilers/munchkin-boiler.html

And this is a Residential brochure for the Munchkin.
http://www.jupiterheating.com/pdfs/munchkin-boukerresidential-brochure.pdf

Cheers man, that was good.

I work at Home Depot in the plumbing dept so i know a good bit about these things.

If i was you i would get a propane fired Tankless heater it would be ideal for your situation and house size. It will cost about 1500 dollars initally if you do the installation yourself but will save you money in the long run and youll have unlimited hot water.
If you have Natural gas service available in your area then use that instead of propane so you wont have to have a tank installed outside.

Also in my house i have a 30 gallon electric tank type heater but i can take 30-45 minute showers without running out of hot water. If you dont want to go with a tankless system you can get some 30 gallon or 38 gallon standard tank type water heaters that are rather small and will only cost a little more than 300 dollars if you can install it yourself.

Whatever you do DO NOT have Home Depot install a tank-type water heater for you. they will charge you 289 dollars just to swap one out and haul off the old one and will ass rape your wallet if the new heater is not the same height and they have to cut the pipes and sweat on new fittings. It's a very simple thing to swap one out but if you cant do it yourself call a local plumber who will probably do it for less than half of what HD charges you. You'll just have to find somewhere to ditch the old heater.

Gas or Electric Califont, Gas Califonts are cheaper than the electrics.
instantaneous hot water on demand.

ok so alot of people have posted here if you choose to listen to me lucky you


tankless water heater: £250 - £800
make one: not sure about price reliability would not be great i have no idea in this section aside maybe using a few kettle elements i would deffinatly buy one i wouldent touch diy too complicated and wouldent save much money

dude, get copper tubing and lay it over a burning pile of tires.


your water will always be hot.

ok so alot of people have posted here if you choose to listen to me lucky you


tankless water heater: £250 - £800
make one: not sure about price reliability would not be great i have no idea in this section aside maybe using a few kettle elements i would deffinatly buy one i wouldent touch diy too complicated and wouldent save much money

Listen to this man.

As a fellow euro (and brit in fact), I want to know where the hell the idea that "it will cost $8000-16000" and "will struggle to supply more than one tap at a time" comes from.

We have a gas-fired one of the described dimensions (3x2x1ft) installed in our utility room, replacing an electrical immersion heater system that used an enormous (50+ gallon?) heavily-insulated yet terribly inefficient copper hot water tank. It can easily supply enough scalding hot water to heat the entire midsize house (3 main bedrooms, 2 reception rooms) to uncomfortably hot levels in subzero temperatures via radiators, at the same time as feeding a shower running directly off its supply and a couple of hot water taps - all using mixer outlets that let in a variable amount of cold mains water to prevent the user losing their skin. We have a secondary 8.5kW electrically heated shower unit that only takes cold water input, and it struggles to match what the gas one puts out - though it remains borderline usable, there's a noticable huge difference in available water heating capacity (the temperature x flow rate = constant law is in effect) in winter time.

And if it cost us more than £1000 ($1500~2000) I'd be very surprised. Installation may have as much as doubled that, but that would have still been on the high end of it. (Though I wasn't involved in the actual billing of it all, it was combined with a general re-engineering and redecoration of the bathroom and the utility room, and we're not rich; more than £3-4000 for the entire long-awaited project would have put it way beyond our reach)

Maybe one that will supply some insanely palatial home in Alaska will be that expensive, but one to supply a small trailer more adequately than your current system should be a three-figure dollar sum. An electrical one may struggle as you'd need a high kilowatt input (and that's even trickier in the states than it is here, with your 110v line level vs our 240v; 100A for an 11kW one, pretty scary current level), but a gas fired one (mainline methane gas if it's available, or bottled methane/propane/butane if not; there may even be oil-fired ones, like my out-in-the-sticks dad's heating system) should manage it easily.

http://www.woot.com/

if you are reading this it's probably too late, but hey if you're browsing, maybe you'll get there in time.

PowerStar Whole House Electric Tankless Water Heater
$249.99

aaaaaannndd too late!