I think that once you start looking at Most folks basements you will find the vertical distance from the shower drain to the building lateral is rarely enough to install a DWR unit. Especially if the home is on a septic system and not city sewer. Typically there's 24" or less drop. I'm not saying flat out that it can't be done but it's not all that often. Also, I'd like to see some real numbers on the ROA for a unit sold and installed by a licensed plumber. I know what I charge for the installation and I'm fairly sure the ROA is a long way down the road especially if the shower is only being used a couple times a day by a couple of older people. As far as the heating system goes, his best ROA is to install the indirect and the intellicon and perhaps downfire the boiler slightly.
The cheapest DWR unit that Home Depot sells is almost 600 bucks and 72" long. The shortest is 48" and almost 900 bucks. Add 30% profit for markup! add all the other pipe! valves and fittings at probably around 200 bucks and then add a couple hours labor at another 400 bucks or so and then run the ROA
And that's a real conservative estimate because the chances of having 4 to 6 feet of un obstructed vertical stack are pretty rare. Usually Theres other drains coming into the line and if it's cast iron you can add a bunch more money to the installation because cutting the cast out and supporting the stack is going to run some bucks. If it was planned on a new installation it would make more sense. They claim 5 to 10% savings. If it's costing say 600 a year for hot water, times 10% that's a whopping 60 bucks. Against a thousand dollar plus installation bill? Still make sense? Other things to consider are the distance from the shower drains to the vertical stack. If it's a long way off the water will cool substantially on its way down the drain, drastically decreasing the efficiency of the unit. Oh yes and one more thing. A whole lot of homes don't have a 4" lateral. Generally it's 3" and only goes through the foundation 4"
So I checked the basement, and we have basically a full floor to ceiling exposed section of vertical cast iron drain pipe (about a foot from the wall? I didn't measure). There are some joins, but I think there were 4 feet of pretty basic pipe there (again, didnt measure exactly, so I guess it could be 3 feet - but I wouldn't want to say without having someone look at it in person). We are on septic, and this drain pipe is well removed from the second floor showers, so I don't know if either of those aspects will affect the usefulness of the DWR unit. I will say that having something that could help with heat recovery sounds really nice if we have to go with a heat pump or electric tank.
From looking at pictures, they all show the recovery wrap around thinner drain tubes, so it's possible that either I wasn't looking at the right stack or it's too big to work, but again, a plumber could probably tell me better.
The installation would mostly make sense for us economically if we were using it for comfort first (to make up for not having an indirect) and energy savings second. That said, if we are spending, say $200 a year on hot water with a heat pump system + DWR (quite possibly less), versus $550 -$50 for an oil indirect + DWR, then that's still a $300 / year savings or a 3-4 year to get back the money for the DWR (assuming that the heat pump hot water tank and indirect oil tank cost about the same to have installed, which it sounds like they do, give or take).
Also, I'm seeing estimates of up to 40% savings on water heating costs (which is 5-10% of total energy costs - bit of a difference). I went ahead and estimated less anyway since there are the other factors (cast iron, distance, etc.). It still seems to come out as worth pursuing, even though it's possible that it might not work in our house.
I appreciate the counter-argument, though.