How to Speed up Delivery of Hot Water in buildings
HOT WATER DELIVERY SPEED UP - CONTENTS: How to get hot water to the plumbing fixtures more quickly. Slow hot water delivery causes & cures. An owner's guide to tankless water heaters - hot water on demand. Tankless water heaters = demand water heaters = instantaneous water heaters. Hot water supply loop circulating systems for plumbing fixtures
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Instant or fast hot water delivery to plumbing fixtures in buildings:
This article explains methods used to speed up the delivery of hot water to plumbing fixtures. This discussion applies to conventional water heaters as well as indirect fired water heaters, tankless coils, tankless water heaters, instant water heaters or "on demand" water heaters.
If you are waiting endlessly for hot water to arrive at your sink, tub, or shower, your home may feel as if the piping is as long and the hot water as far away as if your home were as large as the Victoria Hotel on Victoria Island (above). Hotels use a hot water piping loop or point of use heaters to give guests hot water. Some people make these improvements in their home as well.
How to Speed Up the Delivery of Hot Water in a Building
Portions of the original text of this article was provided courtesy of Carson Dunlop and Rinnai water heaters. Our OPINION is that readers looking for plenty of hot water heated efficiently should also consider the heater we describe at Indirect-fired Water Heaters.
Before you start fixing or buying stuff to fix a hot water problem hot water problems and diagnostic guides for all kinds of hot water troubles are summarized at WATER HEATER PROBLEM DIAGNOSIS. You might want to check there to be sure you're fixing the right problem.
Length of Time for Hot Water to Get from The Tankless Water Heater to the Plumbing Fixture
Unless your hot water piping system is using a continuous hot water loop to circulate hot water between plumbing fixtures and the hot water heater (hotels, perhaps like the Hotel Victoria, Vancouver Island BC, shown at left do this) the time to get hot water from its source to any given plumbing fixture (sink, tub, shower, etc). is a function of water pressure, pipe size, and any obstructions in the water pathway.
The starting temperature of the hot water (from the heating source) is also a factor since the water loses heat to cool piping along the way to its destination.
Water flow obstructions include clogged pipes, clogged plumbing fittings or faucets and valves, flow restrictors, or mixing valves. These conditions exist regardless of how your hot water is made.
Rinnai provides this example of tankless water heater delivery speed:
If your kitchen sink is 50 feet and the water flow rate is 1 gallon per minute than it will take 90 seconds for hot water to reach your sink.
Our photo (left) shows an energy-saving Grundfoss circulator and timer installed on a water heater whose plumbing includes a hot water piping loop through the building. [The plumbing loop is not visible in the picture].
Various plumbing sources including Rinnai offer several solutions to speeding up hot water delivery in buildings:
Place the water heater close to the point of hot water use. This might be easier with a tankless water heater, though plumbing for water, fuel, and also flue gas venting need to be considered. If you need to install many point of use water heaters the cost of providing quick hot water in all of those locations may not be justified
Install a hot water re-circulating line (photo at below left) that keeps hot water following through a loop in your water system and then through the water heater.
Unless you include special controls this is a poor choice because it wastes energy and because running any water heater continuously will shorten the life of the heater and will probably affect its warranty terms.
[Click to enlarge any image]
To make a hot water loop system efficient in a private home or small office (as opposed to hotels where there may be no choice), you'll need to install a hot water piping loop to the area where you want this feature, a hot water pump and control switch, and an occupant sensor switch that turns on the hot water pump whenever someone enters the room and turns the pump off when they leave.
This system will reduce but not always eliminate the hot water delay (how long are you in the bathroom before you turn on the hot water) and it is costly. We don't recommend it for normal residential use.
A simpler but similar system for quick hot water delivery uses a simple timer switch that turns on the hot water pump and loop during shorter times of the day when hot water use is anticipated.
Watch out: as Carson Dunlop Associates' sketch above warns, the constant water velocity found inside of hot water recirculating loops can lead to early wear in water supply piping and thus to leaks.
Install a small electric hot water tank (only a few gallons) to the hot water side of your tankless water heater and run a re-circulating loop through it. Rinnai explains that the tankless system will still heat all the water and you will not shorten the life of your Rinnai or impact its warranty but you will still waste energy.
You could lessen the energy waste by running the pump on a timer.
All of these methods add cost to the hot water production and delivery system in a building.
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Frequently Asked Questions (FAQs)
Some of the FAQs discussed below are adapted from information provided by the Watts Regulator Company in a 1973 publication.
Question: how do I size the T&P relief valve on a hot water recirculating system?
What should be the size of the hot water circulating pipes & connections to keep balanced temperature in the hot water storage tank and to prevent the temperature and pressure relief valve from opening up when it shouldn't? - Watts
Reply: set proper circulating piping diameter
Circulating piping on a hot water recirculating system should be at least equal to the full size of the circulation connection on the heater (the circulating pump connections) and never smaller than 3/4" in diameter.  paraphrased
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Consumer Reports offers an article on the efficiency versus the economy of tankless water heaters - see http://www.consumerreports.org/cro/Appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm
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