A few years ago, one of the first projects we completed at ThisOldFarmHouse was the installation of an electric tankless hot water heater.
The heating system in the house is a hybrid hydro-air system, where a hot water boiler pipes hot water into a nearby air handler and the air handler converts to forced hot air, which is used to heat the first floor via a series of ducts.
Off the furnace was a stand-alone tankless hot water unit, running on a closed loop back to the boiler. While this configuration is just dandy in the winter when the boiler is running all the time anyway to heat the house, it is less than optimal during the April thru November timeframe when, frankly, heating the house is completely unnecessary. Those friends of mine who read this infrequent blog know, the miser I am, I turn the heat off on April 1st and don't turn it on again until sometime in November. Furthermore only Koren and I in the house, so it is rather silly to run the furnance 24x7x365 to support a tankless hot water system which is, at best, used a couple times a day for a shower. (The doggies don't count since they have coats and don't take showers).
After conducting a fair amount of research, I opted to install an electric "on-demand" hot water heater. These units only heat water when hot water is called for, similar to tankless units which run off a boiler, but you don't have to run the boiler all the time to provide the heat exchange source. You turn on the hot water faucet, they heat water, faucet off, they shut off. There are two principle types -- ones that run off natural gas (or propane) and others that run off electric. I didn't want a propane/natural gas unit, as you have to deal with the CO2 issue and they have to be properly vented. Our chimney had issues (other project to deal with later on) so electric seemed to be the logical choice.
There is still a lot of debate whether or not these units save money -- the increased cost of the electric (most expensive fuel source) to heat the water may or may not offset the actual cost of maintaining the boiler on all the time to provide tankless hot water on demand. Another alternative was a separate stand-alone hot water tank (so we could shut the boiler off in the warmer months), but again, with just the two of us in the house and our actual hot water usage being so small, on the face of it I didn't think the standby loss would offset the "higher" cost of using an on-demand unit.
This blog entry is two years after the fact... What I can say about the cost savings is this: Our first year in ThisOldFarmHouse we used the boiler for our hot water, and over the summer we used an entire tank (250+ gals) of oil to provide our heating source for the hot water. After installing the electric tankless hot water unit, we saw our electric bill increase an average of $20 per month (however, it is important to note that with all the construction going on, a lot of electric usage was due to power tools, compressors, etc, so I feel the $20/mo is an overestimate). Though, even at $20/mo, that's still $240/yr, which is at the going rate for oil, roughly 80 gallons... so clearly the unit is a real cost saver in terms of oil-cost vs. electric cost.
However, I digress...
I settled on installation of a Stiebel-Eltron Tempra 36. I selected this unit because a) Stiebel-Eltron is based in Massachusetts, and b) of all the units I looked at, this unit had the most capacity in terms of GPM, so it was suitable as a "whole house unit" (meaning, one unit for the whole house rather than several units spersed thruout). From the writeups I found online it seemed to have a good reputation. The only real competitor was a lessor unit from Bosch, but that unit wasn't really a "whole house" unit but was instead designed for point-of-presence (such as a single unit providing hot water for a bathroom).
Before installing the unit, it was first necessary to have the electrical service at the house upgraded. As you can imagine the house was originally wired for fuses, but had been updated to a small 100-amp panel several decades earlier. Because the electrical demands of the Tempra 36 called for 3 60-amp breakers, our puny 100amp panel wouldn't handle the load. We hired a local electrican who reviewed everything we were planning to do, and upgraded us to a 225-amp panel with upgraded wiring from the pole. The entire electrical upgrade ended up costing $2500, but this was reasonable given we had a lot of other expansion plans for the home which would result in increased electrical demands anyway.
We had the Stiebel-Eltron unit plumbed in such a way that we could switch, via a series of ball valves, from the boiler-based tankless unit to the electric unit whenever we wanted to. Our rationale was quite simple: since we're running the furnace anyway in the winter, why not use it for hot water, and turn off the Tempra-36? Turn some ball valves, turn off the 60-amp breakers, depressurize the lines going to the Tempra, and voila -- we're running off the boiler system for the winter... and come the warm months, when we shut off the boiler... reverse the process, and we're once again on the Tempra unit.
This plan worked flawlessly for the first year. The Tempra unit was installed, and we ran of the unit without a hitch. Switched over to the boiler system in the winter.
The second year we started to have problems with the Tempra. In the middle of showering, the unit would randomly shut off (running the tub always had unlimited hot water). We spent a lot of time diagnosing the problem (Koren watching the unit while I showered). The unit would just seem to randomly power off in the middle of a shower. Eventually, the unit stopped working completely when using the sink faucet for hot water. Talking to Stiebel Eltron's tech support wasn't helpful -- they had me remove and clean out the pressure switches to make sure they weren't clogged. The unit requires at least .7gpm draw to 'detect' hot water usage -- which, for a 2.5gpm shower head, you would think shouldn't be a problem.
This problem was "solved" to a limited degree by changing out our well pressure tank. Koren had mentioned that it seemed our water pressure had decreased since moving in (personally I really never noticed) so I inspected the well's pressure tank and switch. The Well-XTrol pressure tank was close to 15 years old, and while it didn't seem to be water logged, I opted to rip it out and install a new one, along with a new check valve and pressure switch. The total cost of this "repair" was $300 thanks to Lowes, which had all the necessary items, and it took about an hour. I do not know what the old pressure switch (wasn't documented on the tank like it is supposed to be) was set to, but I installed a 30/50psi switch and adjusted the tank pre-charge to match the pressure switch. Upon doing this, the Tempra operated a lot better, but still from time to time one of the heating units would shut off in the middle of use (resulting in luke-warm water rather than cold water).
Fast forward thru another winter of switch-over to the boiler, and switch-back to the Tempra in April of this year.
The Tempra hadn't seen a lot of use over the past few months, for a couple of reasons. First, when we did the kitchen remodel, I opted to install a small Bosch Powerstar tankless electric heater under the sink to provide hot water to the kitchen. This saved me the hassle of running an additional hot water line from somewhere in the basement, I was able to snake a single 1/2" PEX cold water line to the kitchen and generate my own hot water there. That unit uses a single 50-amp circuit, which I tied in from the new kitchen electrical panel.
Second, the latter part of April and thruout May we opted to remodel the downstairs bathroom (having finished the upstairs bathroom as part of the dormer project, which will be featured in an upcoming blog entry)... and, again, the upstairs bathroom was powered by its own Bosch Powerstar AE125 unit (saving the hassle of attempting to snake a hot water line from the basement all the way to the upstairs bathroom).
We started "regular" use of the Tempra unit this season in late May, when bathroom remodeling was finished. The Tempra-36 unit at this point only provided hot water to the downstairs bathroom and nowhere else -- the kitchen and upstairs bath have their own hot water heaters, and our washer only has a cold-water line running to it. So, the only time the unit gets (got) used at this point were daily showers in the downstairs bathroom.
All of this brings us to the point of this blog entry... Yesterday, when not in use, the Tempra-36 unit literally exploded in fire.
I kid you not about this... If it were not for the grace of the Lord Jesus Christ himself (and I'm not a religious guy at all), This Old Farm House would have been no longer of this world.
Wednesday is Koren's day off from work. Only a few moments earlier, she returned from doing some errands in town, and went downstairs to work on laundy. While putting laundy in the dryer (the Tempra was mounted on the wall next to the dryer) she heard a snap and POP, and smoke started pouring out from the unit.
She immediately turned off the 3 60-amp breakers running to the unit, but smoke continued to pour out of the unit. Fortunately, due to all the issues we had with the unit the year before, we did not have the cover to the unit screwed on (merely placed on securely), so she was able to race upstairs, grab a fire extinguisher, and fling off the cover. Red and blue flames shooting everywhere, she doused the unit throughly with our commercial-grade fire extinguisher.
If it had not been Wednesday... had she stopped somewhere else on the way home... had she been delayed at a traffic light for an additional 3 minutes... the house would have rapidly become engulfed in flames and would have been a complete, total loss.
Such is the risk you run living in a 300 year old timberbox constructed entirely of wood -- wood walls, wood ceilings and wood floors. However, it really makes you realize that life is full of chance circumstances, isn't it? Or... is it intelligent design? I'll leave that argument for T's blog :)
A post-mortem of the Tempra shows the following damage (click to see full-size pics):
The fire appears to have started in the circuit board of the right-most heating element. A closer look:
Upon closer inspection, it actually appears that the fire started underneath this circuit board. So, looking under this circuit board, there is another circuit board which handles power distribution from the input block to the heating elements of the unit itself:
Sure enough, that's where the fire actually started. Moving the upper circuit board away for a closer look, we see the complete destruction:
Without further disassembly, it is difficult to tell for sure whether the fire started on the upper or lower portion of this circuit board. However, the entire circuit board at the "base" (which would be the left-side towards the TRIACS) is completely destroyed, with the wires running to the top of the heating element (see picture #1 above) completely melted. I'm not sure we'll ever really know "where" it started... We're only lucky that Koren was home at the time and was able to put it out.
All this happened about 4pm yesterday. Of course Koren immediately called me (I was at work) and told me what happened. While women tend to be hysterical, Koren's pretty level headed, but she was pretty shaken up by the whole thing, especially given the implications if she hadn't been home. I rushed home to assess the damage and to inspect things further. During my 45 minute drive home, I called Stiebel Eltron's technical support department.
Their Tech Support department indicated such a fire was virtually impossible in their unit and that the unit had to have been wired incorrectly. Furthermore, the unit is "UL approved". There are several problems with this theory:
First, the unit was wired corrected with 6ga wire on 3 independent 60amp circuits and correctly grounded per the specifications.
Second, the unit had worked "flawlessly" (except for the water heating issue, which who knows, maybe it was related?) for the past two years... if the unit had been wired incorrectly, I would suspect that it would have experienced an electrical failure a lot sooner.
Finally, looking at another picture:
Electrical power is provided to the unit at the wiring lugs labelled 'L' on the wiring block. If there was going to be an electrical failure due to improper wiring (such as the wrong gauge wire, or arcing due to improper or loose connections), then the wiring block would have been the point of failure. However, as you can clearly see, the wiring block is completely intact. Actually, even the electrical connections on the output side of the block running to the power board are remarkably intact with no melting, so it is clear to me the failure was strictly related to what I refer to as the power distribution circuit board.
Stiebel Eltron is standing by the unit. During my call yesterday, they said they were going to immediately send me a replacement unit... in fact, a 'newer' unit (the Tempra-36 Plus)... which apparently only has a single flow sensor (compared to my unit which has 3) -- and that I can return the damaged unit to them at no cost via a UPS call tag.
While I certainly find it comforting to know that Stiebel Eltron is a company that will stand by its product and provide a replacement... I am extremely hestitant to install the replacement unit at this point in time. I am seriously considering installing another PowerStar AE125 in the downstairs bathroom (which requires 3 40-amp circuits w/ 8-2 wire and a ground) and re-plumb the downstairs bathroom to run off the PowerStar. The only "downside" to this is I wouldn't be able to switch to the boiler-based hot water system during the winter (in fact, I'd probably rip it out entirely and remove all the old copper hot water lines which infest the basement).
I spent time last nite googling tankless hot water heater fires, and wasn't able to come up with anything, other than other people hearing similar stories. I guess we'll see what happens. Maybe I need to install a halon system next to the Tempra if I do decide to install the new one.