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Green Building Blog

Stuff I Learned at Joe Lstiburek’s House, Part 1

Everything I thought I knew about combined hydronic heat and hot water (combo) systems utilizing tankless water heaters is up for debate

Pared-down combined heat and hot water system using a tankless water heater, reflecting lessons learned at Summer Camp 2011.
Image Credit: M. Chandler
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Pared-down combined heat and hot water system using a tankless water heater, reflecting lessons learned at Summer Camp 2011.
Image Credit: M. Chandler
Our in-house combined solar/tankless heat and hot water system. Where the hot water recharge runs into the side of the tempering tank (at about 4-5 gpm), we now use a horizontally mounted perforated solar dip tube to keep from rolling the tank. The flow back from the radiant floor heat exchanger is not so problematic. After this session, I’ll be going to a Vertex tank or a minisplit heat-pump water heater.
Image Credit: M. Chandler
Gary Klein, philosopher laureate of water, me, and Gavin Healy, HVAC provocateur. These guys really give me stuff to think about and have changed the way we build homes — for the better.
Image Credit: M. Chandler
Alex Wilson, Martin Holladay, and Armando Cobo enjoying themselves at the Westford Building Science Symposium.
Image Credit: Armando Cobo
This set up sits next to a 20-gallon under-counter tank in a corner cabinet in a client's guest cabin -- as simple as it gets.
Image Credit: M. Chandler
Split heat-pump water heaters like these will make a big difference once they make it from Asia and Australia to the U.S.
Image Credit:,

The invitation was too cool to be real: My name was somehow on a list of “experts” who were invited to take part in a Building America Water Heater Expert Session on combo systems. The invite noted that the session was to be the day before Joe Lstiburek’s Building Science Summer Camp, and “it is expected that the information obtained will lend itself toward the eventual production of a guide for the best practice application of combination space and domestic water heating systems for new and retrofit residential construction.”

I noticed a heavy representation of tankless water heater manufacturers, as well as researchers and giants of the industry Gary Klein and Larry Weingarten. Martin Holladay was invited as designated skeptic and naysayer, a role he served vigorously.

Needless to say, I got there an hour early

To get us started, Hugh Magande from Rinnai ran us through the ignition sequence of the Rinnai condensing and modulating domestic water heater and discussed improvements they have made to shorten it, especially on re-starts after a brief off cycle, to reduce the “cold water sandwich” problem.

Originally the systems required a ten-second cold fan run to clear any residual propane from the combustion chamber and “prove draft” before starting the ignition sequence. Rinnai has reduced this time; the new range is from 10 seconds to as low as 2 seconds to cold start and shorter for re-start after short off periods (short bursts of hot water in close sequence).

Rinnai has responded to the new ultra-low-flow faucets by dropping the low-flow limit from .7 to .4 gpm for cold start and .2 gpm for re-start, but with less than .3 triggering the shutdown. Once first burn is proved, the two central gas valves ignite and, if water doesn’t come up to temperature, two more light, then two more. Water is heated to as high as 180°F and then mixed down to the set-point by a computerized mixing valve.

Setting the water temperature too cold can cause low-flame issues, so a 140°F set-point leads to the cleanest burn. Cooler intake water is directly related to better energy efficiency. At 100°F the water heater has an efficiency of 91%; at 110°F that drops to 89%, at 120°F only 88%, and at 130°F intake water it drops it to 86%.

Of course, a few years ago we considered 86% efficiency to be pretty darn good, but these days we’re seeking durability and low first cost at 90% efficiency — plus the capacity to provide both domestic hot water and space heating.

What could possibly go wrong with tankless water heaters?

Martin Thomas from NRC (Natural Resources Canada) shared photos of tankless water heaters hooked up to small electric water heaters used as tempering tanks which provide hot water to fan-coil units for forced-air heating systems.

Thomas discussed the problems encountered in these systems: reduced tankless water heater efficiency and perpetually clogged intake filters. Running the tempering loop off the tank bottom at 110°F gives limited opportunity for condensation, but as soon as the water leaving the bottom of the tank exceeds 120°F, you no longer have a condensing water heater. Worse, the warmer water makes the modulating water heater turn down to its lowest setting which, like running a car at 15 miles an hour, further reduces the efficiency of the unit.

People in the audience spoke of measuring the efficiency of on-demand water heaters at about 50% when choked down in this fashion. I have certainly witnessed this problem, as well as soot build-up on heat exchangers when burning propane this way. So if you’re running a tankless water heater to maintain heat on a tempering tank for use in a radiant floor, you won’t get any benefit from using a modulating unit and very little from using a condensing unit.

Non-modulating units are cheaper

The folks from Bosch were very quick to note that their units are non-modulating (and most of them are non-condensing and sell in big box stores for around $600). Here I was installing the best Rinnai and Quietside units and I would have been better off with the inexpensive Bosch from Home Depot, which would probably have allowed me to size the recirculation pump down to a Taco 006 (instead of the more expensive Taco 009s we’ve been using).

Dave Hammond from A.O. Smith spoke about using a fast-acting probe-type thermistor rather than the surface-mounted aquastat typically found on the electric tank water heaters to activate and shut down the recharge pump more quickly, improving system efficiency by reducing recharge time.

A casual side comment made me go “Ah ha!” — when someone spoke of wrapping thermistors in electrical tape to “prevent those problems you get when you have metal-to-metal contact with thermistors.” I’ve sure seen the problem, but never realized the solution was so simple.

Rolling the tank stings two ways

The clogged intake filter problem seems to be related to debris coming from the anode rod. The problem is exacerbated by tank turbulence (AKA “rolling the tank” — when incoming water creates a current that sends hot water to the bottom of the tank and pushes cold water and sediment to the top). So using a smaller pump with a shorter run-time could reduce tank turbulence and help solve this problem.

I spoke about returning the water to the tempering tank using a horizontally mounted perforated “solar” dip tube to diffuse the flow and layer the hottest water into the top of the tank, to press the coldest water from the bottom of the tank to the tankless water heater.

The folks from Bosch proposed that plumbers just remove the filter after two months of operation, as their equipment only needs the filter in long enough to keep any teflon tape and pipe dope from jamming the flow. However, the Rinnai and Navien reps at the meeting didn’t jump on that bandwagon.

It’s Larry Weingarten’s turn

Larry Weingarten from Water Heater Rescue spoke of using a J-shaped cold-water dip tube to push debris up against the drain port, facilitating tank cleaning during maintenance.

Combined heat and hot water systems increase tank cycling and accelerate aging, so tank durability is an important part of this discussion. Weingarten stimulated a glorious conversation with graphic photos of tank failures and premature anode-rod decay. He proposed the idea of buying souped-up electrically powered anode rods and avoiding soft aluminum anode rods, and he explained how to tell the difference between magnesium and aluminum anode rods by looking for a bump on the nut (bump good, flatness bad).

Larry also sold me on using plastic-lined steel nipples to minimize corrosion in the transition between glass-lined steel tanks and brass or copper fittings. He also made a convincing argument to replace the plastic drain port at the bottom of the tank with a proper 3/4-inch ball valve and to take the time every year to flush the corrosive sediment.

The low flow rates of modern WaterSense-listed fixtures has created problems with tankless water heaters that tempering tanks can help address. Larry led a discussion on faucet aerator designs, citing Brycor and Neoperl. You can open up your design choices in faucet selection and just swap out the aerators — the low-flow ones are even helpfully made from green plastic, so the green building rater can verify the swap. We also discussed the pressure drop of different tankless water heaters, noting that the same flow from a Taco 009 pump on a Rinnai would require a Taco 013 in a Navien.

A vote for simplification

Martin Holladay pointed out (vigorously) that we were all going around our elbows to get to our thumbs, by designing and fine-tuning these complex systems when we should just give up and admit that we need one appliance to heat domestic hot water and another to heat the home. (My lead plumber, Matt McDonald, points this out to me on a regular basis, much to my annoyance.) He also noted that most of the suggested modifications to tankless water heaters used for space heating — adding a storage tank, a huge intake filter, and a circulating pump, for example — complicated the systems in the effort to restore the advantages of a cheaper tank-style heater.

Martin loves wood stoves, solar water heaters, and wall-hung minisplit heat pumps, but he has a point. From my perspective, I just can’t imagine building a passive solar house without a well insulated slab floor, and I can’t imagine skipping the opportunity to put radiant piping in a slab and heating it with a water heater, especially with a solar tie-in.

Someone in the audience pointed out that A.O. Smith makes the Vertex condensing tank-type water heater that doesn’t cost much more than a good condensing tankless water heater, and solves many of the problems of marrying a tankless to a tempering tank. The Vertex still hits condensing efficiencies when supplying heat and hot water (or in a radiant floor application). Up to now, condensing tank-type water heaters like Triangle Tube, Polaris, and Phoenix have been much more expensive than condensing tankless water heaters, but it appears that the Vertex at least is competitive with all but the Bosch, which appears to be what we should have been using all along.

Problematical standards, again

The discussion then degraded to raging against the test standards by which these devices are rated. Most excoriated was the ASHRAE 124-2007, “Combined Heat and Hot Water Annual Efficiency Test Standard,” which prescribes supply and return temperatures which may not be the temperatures your equipment is designed for, and further requires that all “smart controls” be disabled prior to testing the equipment. The test gives no way to assess the real-world performance of a system with advanced electronic optimization.

Slightly less vitriol was directed at the Canadian CSA P.9-2011 standard, and mention was made of a new ASHRAE 206 standard for heat-pump water heaters.

I inserted my foot in my mouth by kvetching about how our local HVAC contractors have taken radiant heating away from the plumbers here in North Carolina through activism with their licensing board. My comment fired up the HVAC contractors in the back of the room, who took exception to my complaint. I countered that profiteering by the HVAC industry is slowing the acceptance of minisplit wall-hung heat pumps, because folks who sell ducted heat seek higher markups from systems that are ductless.

We agreed to revisit it at the club house, and eventually all ended well. Last year I ticked off the spray foam industry by bringing up the halogenated flame retardant issue; this year I ticked off the HVAC guys. Joe says I’m not off the list so far, so I’ll see who I aggravate next year.

The elephant in the room

We are all expecting the manufacturers who are putting out these tank-top heat pump water heaters to come out with minisplit versions, where the compressor is located outdoors and doesn’t heat your water by cooling the air that has just been heated by your furnace, but instead harvests heat from outside the house. I assume that they are still working out the issues of stripping the heat off the coil efficiently, and I hope that they will get these products on the market soon.

At this point the Daikin Altherma, Multi Aqua, Space Pak, Unichiller RC, and Aqua Products reverse-cycle chillers are too multi-purpose and expensive to economically serve the simple need to heat a tank of water with a recharge rate of 60 to 140 kBTUh (the typical range for combined heat and hot water systems). Most of these are designed to provide both modulating heat and cooling to fan-coils in forced-air applications.

We need to see a convergence of these technologies, and I think a lot of that innovation will come from the folks at the annual Westford Summer Camp.


  1. Ted Clifton | | #1

    Great Article!
    Wow, Michael, that is why you are my hero! I have to agree with Martin this time, (don't tell him, he will probably croak!) while I will often use heating equipment to also serve my domestic hot water needs, such as in a ground-source heat pump/in-floor radiant application, I believe firmly in heating with a heat source, heating water with the sun, and using light bulbs only for light, not as a heats source, as in the Passiv Haus model.

    Instead of moving the compressor for the heat pump water heater outdoors, we need to get it hooked up with the refrigerator and air-conditioning system. One compressor, inverter style, so it can run at any speed to perform large or small tasks, and use the SAME energy to heat the water that you are using to cool the refrigerator. The compressor installed in the refrigerator should be for backup only!

    We may need to all drink more beer, to "use up" all the cold that will be generated as we are using the water heater to fill our hot tubs...

  2. Expert Member
    ARMANDO COBO | | #2

    Thank you
    Great article, good information and a good summary of the WH Session. Indeed BSC Camp is by far the premier gathering of BS experts, enthusiasts and students, even thought sometimes we don't always agree… and by looking at those pics, it looks like Martin is the ONLY person partaking in the after-hours, eh??? Maybe we’ll get a good recap from Dan, Martin or Carl, with more incriminating pics; of course.

  3. Expert Member
    CARL SEVILLE | | #3

    I got nothing
    No pictures, few notes, an aching neck and arm and drowned laptop is all I have to show for summer camp this year. Hopefully next year will be better.

  4. GBA Editor
    Martin Holladay | | #4

    So how's the aching neck?
    Are you still in pain -- or has the old Carl bounced back yet?

  5. Tristan Roberts | | #5

    dishwashers and on-demand water
    I haven't seen this discussed here or elsewhere, but I can't be the only person with this problem. The flow rate into my Bosch dishwasher is too low to trigger the ignition of my Rinnai on-demand hot water. Fortunately the dishwasher does it in-line, relatively efficiently, but it's still a big electrical load in my off-grid home. I get the hot water "primed" for the dishwasher by running it at the kitchen sink, but I might as well skip the effort, because a minute later the intake to the d/w is 55F. Has anyone solved this? Do the newer low-flow heaters solve this? I don't know what the gpm is with the d/w.

    Thanks for the notes -- very helpful.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Tristan
    I can think of two possible solutions:

    1. Buy a tank-type heater. They cost less than tankless.

    2. Wash your dishes by hand -- a method that is very kind to your home's batteries.


    Dishwasher draw
    I would expect the dishwasher draw to be one to one and a half GPM. I wonder if there is a clogged intake there. No easy way to back wash a dishwasher but I'd check your parts diagram and look for an intake filter. The Rinnai also has a code you can punch into the control pad to get real time read-out of GPM flow-through (great feature) Check if you have the manual that came with your model to find the code. (I think it's hold down priority and hot at the same time for ten seconds but not sure)

  8. Ted Clifton | | #8

    I am with Martin on this, ALMOST...
    We don't know where Tristan lives, if he is in a cold climate, a tank style water heater will be more cost effective, as long as it is a type that can be installed within the conditioned envelope of the house. If he is in a warm climate, buy a heat pump water heater, they have a tank, and they help air-condition your house as they make your hot water.

    Just one final note, the "old Carl" doesn't bounce very well, but he sure is fun to watch!

  9. Tristan Roberts | | #9

    thanks Michael
    Michael, thanks a lot for the tips!

    Martin, we wash plenty of dishes by hand but we like the dishwasher for certain things (like jars) and we run it every 3 days or so. I run it during the day, usually, when there is plenty of sun -- does this reduce impact on the batteries or am I dreaming?

    Are there tank-style propane hot water heaters with sealed combustion? If so I would get one in a heartbeat. If not, I might have trouble getting the combustion gases vented. And I'm not sure my PV system could handle an electric tank.

    I'm in Vermont -- cold.

  10. MICHAEL CHANDLER | | #10

    sealed combustion propane tank
    AO Smith's Vertex is a condensing sealed combustion tank type water heater w/ better efficiency than the Rinnai.

    I see them priced around $1,500 and that would solve your problem. Cheaper to replace the dishwasher with one with a faster fill rate. I don't imagine that filling slowly saves water. I still think the top priority here should be to increase the fill rate of the existing DW.

  11. Ted Clifton | | #11

    The inlet solenoid could be the problem
    Every dishwasher has an inlet solenoid, right where the water supply line attaches to the bottom of the dishwasher. The solenoid opens when an electrical current is applied by the timer. It is possible that the solenoid is old, or just stuck, which I would be more likely to expect of a dishwasher that is seldom used.
    After the water comes in through the solenoid, it is routed up over the top of the dishwasher, where it free-falls into a little cup on the side of the dishwasher, providing an air-gap on the inlet pipe. The water drains from this cup into the inside of the dishwasher, where it does its work. If you increase the flow into the cup, without first assuring that there is no restriction coming out of the cup, you could have water flowing out onto the floor. Considering all the stuff that goes into the typical dishwasher, it is very likely that the bottom end of the tube from the cup to the inside of the dishwasher is clogged, or partially clogged.
    With the dishwasher pulled out from under the counter top, use one of those bendy drinking straws to insert into the cup, and see if you can blow through it. If you feel any resistance, you probably have a clog. This tube should blow through with no resistance. If the tube is clear, and you can safely pour water into the cup with a pitcher and watch it disappear into the dishwasher, then your next step would be to replace the solenoid.
    Before doing any of this, as you are pulling the dishwasher out from under the counter top, check for a kinked supply tube.

  12. user-788447 | | #12

    getting into the nuts, bolts, filters and what have you
    Much appreciated exposition Michael,
    Personally I feel well versed, thanks much to this website, on how to create a kick*** thermal assembly and now much of the attention is towards how best to refine servicing our modern conveniences. Its funny sometimes how creating a low heating/cooling demand structure can create several permutations of how to supply heat, coolth, hot water, and pre-tempered outdoor air most of which the local suppliers have difficultly accommodating.
    An important point I think this article raises is that mechanical systems beyond their efficiencies are equipment and designers like me have little knowledge on what's good and what's crap. Fortunately I have plumbers in the family who can offer opinions based on install experience but I haven't found a good HVAC guy whose brain I can pick.

  13. kevin_in_denver | | #13

    Split Heat Pump Water Heaters (SHPWH)

    It looks like you've scooped everyone with the info about soon to be released split systems. In most parts of the country, these will be just as cheap to run as gas. As discussed in these pages, eliminating the gas service to the house is essential for zero energy homes. (You can't easily generate natural gas and put it back on the grid like PV)

    Deciding where to put today's HPWHs is an awkward problem with awkward solutions:

  14. MICHAEL CHANDLER | | #14

    Where to locate a tank-top heat pump water heater?
    Kevin, I spoke with both Quietside and Rheem at the ASES Solar Conference in Raleigh this spring and both assured me that they had split heat pump water heaters in development. Rheem had a commercial version on the showroom floor, I somehow misplaced my notes on that but you can see their residential unit now available in Australia at was the star of that show as far as I was concerned and I was blown away by their product and failed to take good notes on the commercial split heat pump. I've been really impressed with Quietside demand water heaters and the vibe I got from them was that they were on top of it.

    As far as where to locate a tank-top water heater, it seems like a ventilated attic might be a good possibility. Typically a pretty hot spot and protected from the elements. So long as you get the details right on freeze protection and massively over-size the drainage pan and drain plumbing with a EPDM shower pan and 2" trap-free shower pan plumbing it should be do-able. Still I'll wait for Quietside or Rheem to bring a purpose built split to the US market or use one of the Space Pak or Aqua Products units.

  15. Ted Clifton | | #15

    Nuts and Bolts and J Chestnut (above)
    J Chestnut laments the lack of good HVAC guys to discuss the nuts and bolts of state of the art heating and hot water systems with. I am very lucky, and I cannot overstate the value I have received from working with Barron Heating in Bellingham, WA. They are an exception in the HVAC industry. The problem is one of history, not anyone's fault, just simple history:
    The HVAC industry, for the last hundred years or more, has been based around ducted systems. Most professionals getting into that business were sheet metal workers. They could build a heck of a fine duct system, and they could hook up whatever type of furnace you wanted to that system. Those guys are the ones who own the HVAC companies today, and they are still stuck with the ducted mindset.
    Ducted systems are not dead, but they are of EXTREMELY LIMITED USE in todays world of heating with heat, cooling with air, and making the most of a limited energy resource. Fortunately there is a whole new world of HVAC contractors in development. I have seen some of them come from the commercial refrigeration industry, and others come from the plumbing industry. The really smart HVAC contractors have brought both into their fold, and have developed teams of workers who can really solve HVAC problems on a house-by-house basis.
    It just isn't simple any more, but maybe it will be again soon. Heat with heat, cool with air, and light with light. Good luck, J Chestnut!

  16. GBA Editor
    Martin Holladay | | #16

    Warning to cold-climate readers
    Michael's suggestion to put a water heater in a ventilated attic might work in North Carolina. But please, readers, don't try it in Vermont or Minnesota.

  17. user-788447 | | #17

    HVAC contractors
    I should qualify that when I say I haven't found a good HVAC contractor whose brain I can pick this is not necessarily due to lack of capable helpful people. Working in the small niche market of highly energy efficient custom homes our work does not represent much of a revenue source for HVAC contractors and it reduces their scope of work.

    Previously before my work focused on energy efficiency and the offices that I worked at regularly used a particular HVAC contractor at times I felt comfortable calling them and asking for advice. It was a two way street we provided them some work and they educated us when we asked for it.

    Now with energy modeling we can size our own heating and cooling systems. With the internet and responsive product representatives we can piece together enough information to make choices on the heating, cooling and ventilation equipment we feel best works for the design with an emphasis on trying to minimize these components. Distribution becomes simplified with either point source equipment or home run plastic tubular ductwork.

    The drawbacks in this development are not having the backing of long term experience in installing and servicing the equipment so we don't really know the quality and the durability of the hardware. We are often wanting to use products that the local HVAC contractors don't have experience with. It is understandable that it might not be worth it to them to install this equipment with a competitive bid because they are being asked to take on the responsibility of the product and install warranty on equipment they don't have experience with on a job that represents less revenue to them.

    Things have to change though particularly in cold climates. We use much more energy than we need to condition spaces in the winter. As the housing market continues to crawl I hope local HVAC contractors find ways to service high efficiency designs in a way that can help them meet their own bottom lines.

  18. wjrobinson | | #18

    Instead of air to water (heat
    Instead of air to water (heat pump water heaters, why not water to water, via a drain water heat exchanger. Starting with 70-90 degree water and pulling out the btu's would have a high COP.

    Another overlooked idea is to only run exterior air to water heat pumps for northern winter use during the 6 warmest hours of the day. Just size the system larger and store 18 hours of demand. And back this up w a pellet stove. Done. This system could average what maybe twice the COP of a non storing system? COP 4? Add a cogen to the mix, grab all the exhaust btu's via a heat pump and all gets expensive but the COP goes up to 5, 6 or more?

    Just sayin , ideas for others to run with

    Michael, tell us more with links about "Space Pak or Aqua Products units."

  19. Gregory La Vardera | | #19

    why are we reinventing the wheel
    Has anybody studied the appliance like space/water heater units used in homes in Sweden where most homes have radiant slabs? Why do we struggle to kludge together systems when they make units designed and warranted to do this?

  20. kevin_in_denver | | #20

    Cost and Availability

    Maybe the Swedes do have the magic bullet, but we can't buy it here, can we?

    Also, separate systems have a lot of advantages. Kind of like even though you can buy one appliance that washes and dries your clothes, separate washers and dryers will dominate for a long time to come.

  21. VJyid7azGL | | #21

    Go Simple or Go Home
    Love this conversation. Working on the lowest end of the price scale I lean heavily on simplicity. An electric tank water heater is hard to beat. Low initial cost, low IAQ risk and relatively easy replacement without the need of a financing plan. One question I do have after seeing your photos from the weekend, why do you baby boomers have such a thing for hawaiin shirts?

  22. user-1018399 | | #22

    Re: Clifton comment; Single source multi-modal condensor unit
    Never heard of this idea before but it makes alot of sense. Has anyone seen it done on a small scale residential installation?

  23. watercop | | #23

    What works here in the south
    There's a hot water element to this diatribe...stay with me for a few short paragraphs...

    Here in Florida production builders combine several insanities:

    1) They put hundreds of feet of ductwork mostly used for cooling in the hottest part of the house, the vented attic. Often 2 or more separate heat pumps' ductwork shares the attic since most HVAC contractors are incompetent with zoning, so they throw in another system instead.

    2) The ductwork is generally some or all of: too small, poorly laid out, or leaky. It gains heat from the hot attic (Code compliant insulation merely keeps the ductwork from sweating) Any leaks represent air totally lost to the house so must be replaced with conditioned outdoor air.

    3) Oh yeah - homeowners pay hundreds per month to cool their houses by pumping heat outdoors and then pay again for additional energy to heat domestic water.

    We fix all that. First we foam the attic roof sheathing, "deventing" the attic and dropping temps 40*F or more. Any air leaks from ductwork stay in the air sealed envelope. This cuts load, generally allowing us to shed at least one system and several tons capacity. The formerly undersized ductwork becomes right sized, and we add zoning so system follows daily load and occupant needs.

    Here's the hot water part:

    We add a refrigerant desuperheater to transfer heat from the HVAC to an unpowered 80 gallon storage electric water heater. That tank feeds preheated domestic water to any type of downstream water heater, be it gas or electric, tank or tankless,

    The system provides free hot water all summer and cheap hot water during cold weather

  24. Ted Clifton | | #24

    James & Curt...
    James, I have seen, and built, many commercial and industrial sized systems using heat harvested from refrigeration systems to heat the building. This is commonplace in grocery store construction. It is also very common wherever Hockey and swimming are enjoyed. Everywhere I have lived in Canada, the local Sports Centre (Canadian spelling) harvests the heat from the ice rink to heat the swimming pool. The first such system I personally visited was more than thirty years ago. I have not seen it on a residential scale, however, and that disappoints me.
    Curt, you are the bright spot in my day!
    Now we need to figure out how to cook food with a heat pump, harvesting heat from the refrigerator. When I was driving truck for a living in rural Alaska, we used to heat up our lunches by placing them on the exhaust manifolds of the diesel engines. It could get as hot as 1,400 degrees F! Perhaps when we pull into the garage at the end of a hard day's work, we should just pop dinner under the hood for a few minutes, and justify the fossil fuels we just burnt up getting home from work.

  25. mCrVWF35LW | | #25

    Tankless water heaters
    More than fifty years ago Feranti from Italy sold a heat pump that could be placed in an insulated closet, the machine about 2'x1'x3' high produced ice in a shelf cooled the closet like a refrigerator and passed the excess heat to the hot water tank. What a great idea. Do we have anything like this on the market today? Please email me if there is.
    Bob Frew [email protected]

  26. jnarchitects | | #26

    Tankless or not to Tankless
    At our office we end up debating tankless or gas fired storage tank on almost every project. It typically just comes down to the type of HVAC that is being employed. Is it a straight forced air system, straight hydronic or some combination.

    For my own house, after much debate and discussion with the plumber I went with a Rinnai unit. It has been great so far, but I definitely have some complaints. Mostly, I am concerned with how much water is wasted waiting for the water to heat up. It is relatively quick at most locations, but the kitchen sink is the furthest from the tank and takes a couple of minutes to reach temperature.

    The other concern is how often the unit fires on without ever getting hot water. If I am quickly washing my hands or brushing my teeth, the faucet might only be on for 10-15secs at a time. We have single lever faucets, so every time you turn on the faucet there is a call for hot water. The machine probably cycles on and off 5-6 times per day when we don't need hot water. Not sure that there is a way around that....

  27. MICHAEL CHANDLER | | #27

    More detail for them what wants it
    Armin Rudd's draft report on the event is available. E-mail me - Michael @ - if you want a copy of the summary with the attendee's e-mail addresses removed

  28. DennisDipswitch | | #28

    Further Updates?
    Michael,great article,made more so by your experience in actually implementing these systems yourself.I was lead to this article by your article in Fine Homebuiding,January 2008,concerning the tankless water heater and the small buffer tank.I hope you can discuss this further.

    I am wondering if you have further refined the system?

    it would seem that the variables may be,tank size and type,temperature monitoring of the tank water,pump sizing and that pesky inlet water filtering issue.This seems to be the biggest hurdle,certainly displayed in the Armin Rudd/NYSERDA Utica,NY installations.I am wondering if you have experienced the excessive inlet clogging in your own installations?

    Maybe you could discuss a few other topics as well.One might be pump sizing.In your FHB article you suggested installing the large Taco 009 pump.I wonder if smaller pumps may work as well?Please explain if moving water very quickly through the tankless heater is really desirable.Is the idea to move water quickly or agitate the contents of the tank?The large pump would seem to be a large draw of electricity,especially at start up,considering that with a small tank there must be plenty of short cycling.

    Is the use of this tank(a converted,disabled electric hot water heater) because there is nothing available that may be better suited,say a small stainless steel indirect tank with coil?

    And with regards to the tank,what determines the desired sizing of it? Could it be smaller than 10 gallons,larger than 10 gallons,much larger?Standby losses and short cycling of the tankless heater would seem to be a concern.

    Thanks Michael,for all of your contributions,and I hope you can discuss this further or direct us to where these topics have been discussed recently.

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