Hello,

I just recently moved into a new residence just North of Toronto, Ontario and have a hydronic radiant floor heating system installed under ceramic tile in a 10' x 30' extension...This extension also has 3 large exterior windows along the 30' ft length which faces north and constructed from brick veneer walls with approximately R20 insulation. Both the extension and the radiant flooring system were constructed approximately 10 years ago. 

The radiant floor has a 40-gallon hot water heater as its hot water source which is pulled through a Polaris single wall heat exchanger...The reason for the Single Wall Heat Exchanger is to isolate the potable water supply as the 40-galon hot water heater is also used for our domestic hot water use.  The radiant system has 2 Grundfos 59896161 UP15-42F pumps....Each pump is used the cycle the water through their respective in/out heat exchanger ports....2 Pex Pipe Loops going out and returning back to 2-independent dual port manifolds, and the hot water heater tank temperature is set at 160F.  The system also has a EEMB mixing/diverting valve with the max setting set at 120F installed between the single wall heat exchanger the the out-manifold which supply hot water to the floor.

As the weather has noticetable begun to get colder, below are some observations on how the system is working;
1. The floor closest to the exterior wall is cooler.  I also noticed that the temperature of this returning pex pipe loop, as opposed to the other on the interior second half of the room. is also coller.
2. The system is only able to increase the room temperature to approx. 23 degrees celcius.
3. After taking a 10-minute shower I noticed that I am slowly running out of hot water.

I am thinking of eliminating the single wall heat exchanger and tying the radiant floor heating system to a dedicated hot water heater system.  This would also allow me to decrease the Hot Water Tank Temperature down to ~ 120F and hoperfully run a more efficient system.  Due to limited space and venting options, I am unable to install another tank-type hot water heater.  I have also been told that I cannot install a Natural Gas Tankless Water Heater which would share the same atmospheric vent as the domestic tank hot water heater.

Therefore, I am thinking of proceeding with installing a electric type 10,000 BTU system running on a 240V circuit...I would appreciate your comments back on your ideas and experiences which may be helpful to my current situations.  Please also comment on the following;
1. Is a 10,000 BTU Electric Type Water Heater sufficient to meet my Radiant Floor Hot Water Needs.
2. How efficient and expensive, from a monthly operating cost, would the electric system be?  The current electic cost per KW is $0.07 and Natural Gas is $0.12 per M3. 

To fix the shower situation, install a drainwater heat recovery heat exchanger (DWHR) and enjoy the best of all worlds- higher efficiency, and (nearly) endless hot water for showering. In most of Canada there are incentives for installing them too. It won't improve the tub-filling capacity though. It's worth buying the fattest and tallest one that fits, since both height & girth increases the heat exchange surface area for higher performance.

See: http://oee.nrcan.gc.ca/residential/personal/retrofit/13302

http://www.sears.ca/catalog/power-pipe/13684-138-100002080

http://www.homedepot.ca/catalog/drain-water-heat-recovery/173006

A 3" x 60" or 4" x 48" or larger is usually good for a 50%+ return of heat used by the shower, and the burner would essentially keep up the combined HW and space heating loads.

I currently have a 4" x 48" unit on my system, and have the set the hot water temp to 130F, (no mixing valves.) Even when the heating system is pulling 40KBTU/hr (a hydro-air zone) I can still shower just fine pretty much forever. YMMV (Without the DWHR I'd be in divorce court already. :-) ) With better heat exchanger plates on my radiant I could probably drop the temp another 10F and get about the same space heating performance, and run deeper into the condensing zone on water temps without taking a hit on DHW performance.

Cranking the HW heater up to 160 isn't buying you very much in extended showering performance, but it does keep it out of the condensing zone. If it's not a condensing HW heater you have to keep the temps up somewhat (not 160F though) to avoid destructive flue condensation when running with low temp radiation. As long as the return water from the HX entering the tank is at 130F or higher you're pretty safe- you might be able to get away with 120F return water, but not lower.

The plate heat exchanger is must be in place. The loss is through the HX is of little consequence if not plugged by either end. Soft water is a must and circulators are suspect. If the system was working well, then the system is not the problem. Good old-fashioned maintenance would be the key here. Maybe dare I say, professional maintenance.

At least you could stay on topic and not get distracted with gray-water recovery gadgets. Seriously, the pennies saved won't pay for the ink to write about it.