Monthly Archives: December 2010

DWHR installation

My DWHR unit, or heat exchanger, arrived and I was interested to see if I could manage the installation. The manufacturer provided some good instruction, so I expected the task to work out fine.

I started by tying into the four inch sewer connection near the utility wall. I ran a two inch drain pipe with a slope of at least ¼ inch per foot (or 2%) to the DWHR location.

Because of the heat exchanger weight, I placed a support under the drain pipe near the end and installed a 90 degree long sweep elbow.  I was then ready to connect the DWHR unit.

A Fernco sleeve takes care of the bottom connection, while a ProFlex™ connector is used at the top of the heat exchanger. It provides an almost seamless surface on the pipe interior, which allows the hot drain water to cling to the pipe wall for the best heat recovery yield.

The double wye at the top of the heat exchanger picks up the 1st floor bathroom floor drain, the 1st floor shower drain and the 2nd floor shower and floor drain. The bathroom floor drains are connected to this stack, because it is the simplest and most efficient routing.

I placed the DWHR unit with enough room to the back wall for the ¾ inch cold water connection and pipe insulation.

I will have to take care of the cold water connection, but decided to leave that task for after the basement insulation is complete.

Happy New Year!

That heat is mine, and I plan to keep it!

I have been in framing mode, after having closed up the old basement stairs. I thought it was a good idea to tackle the 1st floor bathroom floor next.


But… there is always a but. This one has to do with plumbing. I have to install the water closet drain, floor drain, and the bathtub/shower drain for the 1st floor bathroom. Along the way, I should think about energy conservation.

All right then, let’s put the framing square aside and get the pipe wrench out.

Plumbing and energy conservation

To reduce our energy load, we included a drain water heat recovery (DWHR) unit in our plans. The DWHR is a heat exchanger with a copper drain pipe that is tightly wrapped with small copper tubing coils.

The unit is installed in a vertical drain stack. The drain water coming down the stack tends to cling to the pipe walls because of the water’s surface tension.

While hot drain water flows down the copper pipe in the DWHR, fresh cold water is flowing up the heat exchanger in the coils and, in the process, picks up the heat from the hot drain water.

In other words, hot drain water enters from the top and leaves cold at the bottom, while fresh cold water enters at the bottom and leaves warm at the top. Makes sense, doesn’t it? Let the drain water go, but keep the heat for which I already paid.

Not recovering that heat can get expensive. The Department of Energy estimates that 80% to 90% of the energy we put into hot water is lost down the drain.

Because the DWHR process relies on the drain water surface tension, it is only effective in vertical applications. The longer the heat exchanger unit, the greater the heat recovery. Also, a larger pipe diameter in the heat exchanger typically yields a better recovery rate.

See also: – Drainwater Heat Recovery

Side note:

A DWHR can lead to pressure loss in the cold water supply, while it is flowing through the small coils around the heat exchanger.

By running multiple coils in parallel around the central drain pipe, some manufacturers have overcome the pressure loss problem. This is something worthwhile to look out for.

Location challenge

What is the best, or the most effective location for the DWHR unit in our plumbing system?

It should be installed at the lowest point possible, which would be somewhere in the basement. That would allow us to pick up and recover heat from the 1st and 2nd floor drains.

Because the heat exchanger would be located on or above the basement floor, we cannot route any of the basement drains through the unit, thus we will not be able to recover any waste heat from basement fixtures.

Waste heat sources

What generates hot or warm drain water that should be routed through the heat exchanger?

The water closet flushes with cold water. No energy recovery there.

The clothes washer is in the basement, thus below the heat exchanger. That doesn’t matter too much, as most of the laundry is done with cold wash cycles these days. Not much energy recovery there either.

What about the sinks in the kitchen and bathroom? There will be some potential for drain water heat recovery. Considering our plans for WaterSense low flow fixtures and the very intermittent use, I suspect a very small recovery yield.

The dishwasher uses hot water. The problem is that it doesn’t draw any cold water when it discharges the hot water. I need both at the same time for the heat exchanger to work.

There are the showers. They will also be fitted with WaterSense low flow fixtures, but they will run for at least five minutes. And I will draw cold water through the heat exchanger while I have the hot water from the shower going down the drain.

After consulting with some energy experts as well as with manufacturers of DWHR systems, I was reassured that I will get the biggest bang for my buck by recovering waste heat from the shower drains.


Quick recap: The DWHR unit will be somewhere in the basement where it can pick up the drain water from the 1st and 2nd floor showers.

The 1st and 2nd floor showers should drain through their own two inch drain stack routing the water into the heat exchanger. The bottom of the heat exchanger will be connected to the sanitary sewer.

Careful placement of the DWHR unit into one of the basement storage rooms leaves the door open for a future gray water collection system. It would fit in the space between the heat exchanger and the sanitary sewer.

Closing up the old basement stairs

We have two very big holes in the basement ceiling that we need to plug. There is the opening were we had the old basement stairs, and the missing floor in the 1st floor bathroom.


I decided to start closing up the floor at the old basement stairs and gathered  a couple of 2 by 12 floor joists, some joist hangers and some left-over plywood sheets .

The new floor will turn the old staircase into a new first floor pantry/storage closet.

Although the existing staircase walls to the left and right were originally cantilevered by a few inches, I felt that it would not hurt to add some support.

To the right, I sistered a two by four to the existing floor joist. It now sits under the bottom plate of the existing wall framing.

To the left, I snug the floor joist partially under the bottom plate of the existing wall framing. This should add sufficient support to the wall as well as the new floor.

Two layers of my left-over plywood became the pantry/closet subfloor.  It sits flush with the existing subflooring to the left and right.

That is one big hole plugged and one small step closer to the basement insulation.

What’s next?

A great weight fell off our shoulders with the passing of another major milestone: heat in the basement. Although it is the basement only and not much is insulated yet.

What we got insulated is the basement floor with rigid foam boards. We also put in the bond break around the basement floor, insulated around the basement windows and installed an additional thermal break onto the window buck.

The next logical step is to get heat into the 1st and 2nd floors and insulate the whole building. Logical as it may be, we also have the big urge to move into the basement – the garden apartment – as soon as we possibly can. Once we live in the building we can continue our work on the 1st and 2nd floors.

In the interest of time, we decided to postpone the heating and insulation work on the 1st and 2nd floors. Instead, we will channel all our efforts into the garden apartment, and continue with insulation preparations. We have the perimeter walls framed out and ready, but more prep work is needed.

I put the usual to-do list together – a list with some major tasks on it:

  1. Frame out the floor at the old basement stairs;
  2. Close up the floor to the 1st floor bathroom;
  3. Install the drain, waste and vent (DWV) plumbing to the 1st floor bathroom; and
  4. Eliminate the thermal breaks along the exterior walls.

Well, what are we waiting for?

The heat is on!

The big day has come. The hydronic heating system is filled with water and Mariusz has come out to start up the system.

He switches everything on and tinkers around with the controls on the boiler. He keeps tinkering but the system just doesn’t want to start up. Should I worry about this?

Sometimes there are simple solutions to apparently complicated problems. As we were getting nowhere, Mariusz took a step back (literally – he stepped out of the utility room) to look at the big picture. I then saw the light bulb coming on. He stepped over to the shut-off valve at the water main and opened it. Of course! A hydronic heating system won’t work without water!

Within seconds the boiler fired up (which is hard to hear because it is so quiet). The pressure gauges kicked in and the pumps began to work, and with a lot of gurgling in the pipes. The temperature gauges at the storage tanks started to climb and the hot water began to flow.

We could see and feel the water running through the PEX loops that feed the radiant floor. I had fun watching Mariusz calibrate the flow rate for each loop at the manifold.

We had, however, two loops that for some reason had no water flowing. That sort of freaked me out. I already saw myself breaking up the new concrete floor trying to find the flaw in the PEX tubing!
Thank God, there was again a simple solution to the problem – a problem that I had caused.

The inlet and outlet for each radiant floor loop are right next to each other, with the exception of the two non-working loops. Here I had placed the two inlets and two outlets side by side.


That meant that the hot water was pushing in from both ends, or trying to get out from both ends. After consulting with Peter, Mariusz quickly identified the problem, switched the PEX connections around and got the hot water flowing.

I can’t tell you how nice it feels to have this nice, warm radiant concrete floor in the basement! The dog likes it too!


Happy Holidays!