Drainwater Heat Recovery

Drainwater heat recovery (DHR) is a very simple and effective means to recapture heat that is otherwise lost to the drain. There are many ways to save on water heating costs but a DHR unit is definitely the most cost effective.

Imagine it as your shower preheating itself. The falling drainwater passes through a double walled heat exchanger whilst the cold water destined for the water heater and shower is also routed to the heat exchanger to absorb most of that valuable heat. Through the DHR the cold water temperature is raised 10+ degrees C meaning the water heater runs for a shorter amount of time.

Lower water heating costs
- up to 40%
Extend Hot water Capacity
Reduce Carbon footprint - up to 1000kg
Increase life of water heater
Zero maintenance, self cleaning and no moving parts
Long lifespan -- all copper construction


Merlyn recommends and installs only the Power-Pipe® brand DHR units for their superior design, durability and that they're locally made in Waterloo, Ontario.


Guide to retrofitting a DHR unit into your home
Power-Pipe price list

Frequently Asked Questions

How much could I save?
How do I know it works?
How would I know if a Power-Pipe® can be installed in my home?
Does the device save me on all hot water draws?
What if I have multiple drains?
Can I install the unit myself?


How much could I save?

Being an efficiency measure, logically the more hot water you use the more you save with a DHR. Also, the higher percentage of hot water use taken by showers in your home the more you will save. Efficiency of the DHR units varies by length, ranging from 15-75%, 40-50% being most common. So, if the showers in your house represent 50-70% of your hot water and the DHR is saving 40-60% of that load, the savings are in the range of 20-40% of your hot water costs.

How do I know it works?

The energy savings of a drainwater heat recovery unit have been verified by Natural Resources Canada and are included as a grant worthy option under the ecoENERGY for Homes program. Some utilities also support the installation of such units with on-bill credits and other incentives.

Once you have one installed, you can feel for yourself the temperature increase across the heat exchanger when someone is having a shower. That temperature difference (15-25C) is heat your water heater doesn't have to produce.

How would I know if a Power-Pipe® can be installed in my home?

DHR units can be installed in most, but not all homes.

Generally speaking, newer homes with finished basements are not likely to easily support a DHR install. They have multiple drainstacks and are often drywalled in bulkheads with drywalled ceilings. If you're lucky a shower rich drainline will be located in the mechanical room right near the softener. Side split homes are also trouble, as the showers usually sit on the split with the drainline coming down to the basement on an angle, not presenting much vertical height to work with.

1) First question we ask is "Can you see your drainstack in the basement?", if the answer is "No" then chances are slim that DHR will be easy or feasible to install. The drainstack must be fairly easily accessible to be cut out and replaced with the DHR unit which is usually 48-72" long.

2) Secondly, how much vertical, uninterrupted, drainstack is available? The heat exchanger should only ever be installed vertically and should be at least 36".

3) Thirdly you must be able to route the cold water lines to the heat exchanger and back. Cold water is usually intercepted after the softenener (or water meter) and sent to the heat exchanger and back. Using only the cold water feed to the water heater is also an option, however it is slightly less efficient than having all the home's water running through the heat exchanger.

Read this retrofit guide for more information.

Does the device save me on all hot water draws?

No, the DHR unit functions effectively when there is a simultaneous draining of hot water and a flow of hot water. This essentially limits it to showers, luckily enough showers represent most of the hot water use in a house (a generally accepted estimate is 50-70% of a typical family's hot water). When you have a sink of dishwater or a bath, you are draining the heat without any flow of cold water to pick it up. It is true that the small amount of water sitting in the heat exchanger will absorb that heat and either be available for a limited time for the next hot water draw or ooze into your house, a small savings.

DHR units also cannot save any of the heat from showers located in the basement because the drain is below the heat exchanger.

What if I have multiple drains?

A multiple drain scenario is likely in homes built after 1990 or any home with extensive renovations/additions. The trend of master bedrooms with ensuite bathrooms saw drains spread out around the house. As discussed above, the DHR unit will only effectively save the energy of the showers so those drains that carry the shower water are of interest. It may be the case where several showers are split amongst the drains -- here the shower that sees the most regular use should be the target. It is still quite reasonable to install multiple DHR units however the financial return will be lower.

Can I install the unit myself?

Yes, the handy homeowner can install a DHR unit without much trouble. Skills and tools required must accommodate cutting and removal of the drainstack (ABS/ copper / cast iron) and the plumbing work to re-route the cold water in copper or PEX tubing.





The average price of a DHR unit, including installation and taxes is $950.

This will vary depending on the unit size and ease of installation, a range is $700 - $1200

View the Power-Pipe® unit price list.


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