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Thread: Reduce lag time for tankless

  1. #16

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    Quote Originally Posted by philp View Post

    We chose tankless because we wanted the extra space (I can build a home theatre in my basement now!) but I wouldn't recommend tankless to anyone who doesn't have a space issue.


    I changed to a tankless for the same reason. I needed the floor space for other uses.

    However, I prefer to have the unlimited hot water that the tankless provides.




    Quote Originally Posted by philp View Post
    Thanks zl700 and ChuckS.

    It looks like I will have to live with the delay. It is not a problem for showers or dish washing - an extra 30 seconds you just get used to and plan appropriately. However, it means I never get to wash my hands in warm water - I'll have to see if I can get used to that.

    By the way the PEX is 1/2". I like the idea of recirculation if it means no wasted water while waiting for it to heat. I'll talk to my installer, thanks.


    How many times a day do you wash your hands at home? I guess you are going to have to either wait a few seconds and let the water get warm, or you can simply rough it out washing your hands in that freezing cold water!

    The only time of the year that the "cold" hot water bothers me for hand washing is in the middle of the winter. Most of the year the cold water is at room temperature. Since I am a manly man I rough it out washing my hands with 70 degree water.
    Samuel James Witwicky

  2. #17
    DIY Member ChuckS's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    The only time of the year that the "cold" hot water bothers me for hand washing is in the middle of the winter. Most of the year the cold water is at room temperature. Since I am a manly man I rough it out washing my hands with 70 degree water.
    I use cold also, I wish my wife and daughter would but that isn't a fight worth fighting. I actually saw a increase on the gas usage on my bill while my daughter was on summer break. In addition to turning on the hot and waiting for it to get hot to wash her hands she also turns on the shower and does other things while it "warms up". That is one draw back to a tankless, she is now complacent to the shower "warming up" since the hot doesn't eventually run out.

  3. #18
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by ChuckS View Post
    In addition to turning on the hot and waiting for it to get hot to wash her hands she also turns on the shower and does other things while it "warms up". That is one draw back to a tankless, she is now complacent to the shower "warming up" since the hot doesn't eventually run out.
    If it was a tank system you could install one of those "Ladybug" ShowerStart valves. It automatically cuts back to a very low flow (they say "trickle", I say more) when the temp reaches 95 F. Just pull the toggle when you are ready to shower and the flow resumes, very little waste. Guess that won't help much with tankless though as it will drop below the minimum and create a cold sandwich.

    I've had some interest in tankless, but the more I listen, the fewer real advantages I see to them vs. an optimized tank.

  4. #19
    DIY Member flamefix's Avatar
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    Quote Originally Posted by Runs with bison View Post
    If it was a tank system you could install one of those "Ladybug" ShowerStart valves. It automatically cuts back to a very low flow (they say "trickle", I say more) when the temp reaches 95 F. Just pull the toggle when you are ready to shower and the flow resumes, very little waste. Guess that won't help much with tankless though as it will drop below the minimum and create a cold sandwich.

    I've had some interest in tankless, but the more I listen, the fewer real advantages I see to them vs. an optimized tank.
    What flow would it restrict to? Most modern demand driven boilers here would work at lower flow rates say 2 -3L/min so perhaps it may work. Can you give me a link to this valve?
    Gas, Oil, solar and renewable service and installation in Devon UK- Please note my advice is not based on USA regulations as I am UK resident. Therefore I will try to avoid posting where confusion may be caused or make that clear.
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  5. #20
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by flamefix View Post
    What flow would it restrict to? Most modern demand driven boilers here would work at lower flow rates say 2 -3L/min so perhaps it may work. Can you give me a link to this valve?
    http://evolveshowerheads.com/ladybug_showerhead.html

    I haven't bucket tested the trickle (it varies somewhat) but estimate the flow at perhaps .1-.2 gpm (US), perhaps less. That is well below the ~0.5-0.75 gpm threshhold for a tankless heater, so I suppose it would shut down. Depending on how long it takes before restart the cold sandwich could be very small I guess.

    The low flow showerheads I'm presently using might even be borderline for tankless in summer as the heads require only about 0.8 gpm of hot water @120 F for the mix with the flowrates I'm seeing.

  6. #21
    DIY Member philp's Avatar
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    Quote Originally Posted by Dana View Post
    Option # 1 is probably the right one. ...They make a 6 gallon version, but that's overkill for handwashing- might be worth it if you have 2 bathroom sinks and a kitchen all drawing from it though. It takes up a bit more space than the others though- harder to jam under some sinks.
    Great info - thanks!

    I'd like to put it under the kitchen sink (minimal lag time here would be the most useful) but I'm worried that at some time we would need more than 2 or 4 or 6 gallons of hot water at one go. Is there a way of switching back to the tankless if we needed a lot of hot water? e.g. some sort of valve that could be turned manually?

  7. #22
    DIY Member flamefix's Avatar
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    Quote Originally Posted by Runs with bison View Post
    http://evolveshowerheads.com/ladybug_showerhead.html

    I haven't bucket tested the trickle (it varies somewhat) but estimate the flow at perhaps .1-.2 gpm (US), perhaps less. That is well below the ~0.5-0.75 gpm threshhold for a tankless heater, so I suppose it would shut down. Depending on how long it takes before restart the cold sandwich could be very small I guess.

    The low flow showerheads I'm presently using might even be borderline for tankless in summer as the heads require only about 0.8 gpm of hot water @120 F for the mix with the flowrates I'm seeing.
    I couldn't find the flow reduction rate in the datasheet. Some boilers like the Viessmann have a comfort setting which keeps the water within the boiler pipework at temperature which may be sufficient for the lag of the boiler firing up and providing hot water, for anyone else thinking about 'tankless'.

    Two country's separated by a common language color, colour, tankless instantaneous water heater, plus the Atlantic of course
    Gas, Oil, solar and renewable service and installation in Devon UK- Please note my advice is not based on USA regulations as I am UK resident. Therefore I will try to avoid posting where confusion may be caused or make that clear.
    http://www.flamefix.co.uk

  8. #23
    In the trades Dana's Avatar
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    Quote Originally Posted by flamefix View Post
    I couldn't find the flow reduction rate in the datasheet. Some boilers like the Viessmann have a comfort setting which keeps the water within the boiler pipework at temperature which may be sufficient for the lag of the boiler firing up and providing hot water, for anyone else thinking about 'tankless'.

    Two country's separated by a common language color, colour, tankless instantaneous water heater, plus the Atlantic of course
    It's worse than that- there are regional & local variations in the US too (some call them "on-demand water heaters") as well as confusingly similar terms in use here like "tankless coil" (a heat exchanger located inside a hydronic boiler for potable hot water.) "Tankless" seems to be the term in broadest use here, as a means of distiguishing them from the ubiquitous storage tank water heaters used here. In much of Europe tank heaters are at least as rare as the copper finned water-tube boiler "tankless" type heaters are here. (I can't recall having seen any tank-type water heaters in the Netherlands when I lived there. Most homes there had two water heaters, one for the bath/laundry, and a smaller one for the kitchen. ) I'm not sure what the relative distribution is in the UK.

  9. #24
    DIY Member ChuckS's Avatar
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    Quote Originally Posted by Runs with bison View Post
    http://evolveshowerheads.com/ladybug_showerhead.html

    I haven't bucket tested the trickle (it varies somewhat) but estimate the flow at perhaps .1-.2 gpm (US), perhaps less. That is well below the ~0.5-0.75 gpm threshhold for a tankless heater, so I suppose it would shut down. Depending on how long it takes before restart the cold sandwich could be very small I guess.

    The low flow showerheads I'm presently using might even be borderline for tankless in summer as the heads require only about 0.8 gpm of hot water @120 F for the mix with the flowrates I'm seeing.
    Bingo, our tankless has a .5 gal minimum. We have waterpik ecoflo shower heads with the trickle setting but can't use it or the sandwich will get you if the loop has turned off. Now it would work while the loop is on BUT her showers go long after the loop shuts off.

  10. #25
    DIY Member flamefix's Avatar
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    Quote Originally Posted by Dana View Post
    In much of Europe tank heaters are at least as rare as the copper finned water-tube boiler "tankless" type heaters are here. (I can't recall having seen any tank-type water heaters in the Netherlands when I lived there. Most homes there had two water heaters, one for the bath/laundry, and a smaller one for the kitchen. ) I'm not sure what the relative distribution is in the UK.
    So are your hot water cylinders (tanks) not made from copper? They are here and europe or Stainless steel. In Germany now the move is away from Copper altogether towards stainless steel tanks and pipework or plastic pipework.

    Having the two heaters makes sense for short draw hot water demand at the sink, or electric under sink 15litre heaters currently subject to boiler location you can get long draws before hot water hits the tap, resulting in cold water hand washes.

    Generally you'll find apartments and such high density housing have tankless systems installed. Some like in Poland that I have seen are on a form of district heating. In Germany I couldn't tell you the proportion but anyone with a basement will have at least a 500litre storage tank if not 750 to 1000litre. This will be supplied with solar and gas/oil/wood/pellet fired boiler.

    In the UK it was traditionally a tank and separate boiler, the system was generally open vented(ie atmospheric pressure not sealed) but from the late 70's combi boilers were introduced (I believe by Vaillant group) House builders took to them with relish as it freed up space in the house and cut down on installation time. Therefore a majority of houses are fitted with combination boilers, but not all some are still fitted with a system boiler and cylinder(tank). There are even some combination cylinders with inbuilt condensing boilers pressurised hot water to supply higher flow rates for power style showers.

    With current building regs here The latest round of Part L here is a further drop of 25% in energy usage on new build but not legacy(grandfathered) build. Moving towards 2016 when all new build property has to be low energy carbon neutral. I think we are looking at space heating requirements of 4kW heat input.
    Gas, Oil, solar and renewable service and installation in Devon UK- Please note my advice is not based on USA regulations as I am UK resident. Therefore I will try to avoid posting where confusion may be caused or make that clear.
    http://www.flamefix.co.uk

  11. #26
    DIY Junior Member rob27's Avatar
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    Default Hot water up 3 floors

    Quote Originally Posted by philp View Post
    We installed a Rinnai tankless hwh two months ago. Now it takes about 30 seconds to get warm water and 40 to get hot. With our old electric hot water tank it used to take under 15 seconds to get warm and 20 to get hot. (I tested this first thing in the morning when the hot water hasn't been used for many hours.)

    I think the main problem is that the tankless hwh is located much further away from all the hot water faucets - but it doesn't matter which faucet I test this on. The "pipes" from the tankless are PEX - about 25' until they tie into the copper - could this make any difference?

    Does anyone have any tips on reducing the lag time from turning on a hot water faucet to actually getting hot water? I guess we could move the tankless closer to the faucets - is there any rule of thumb for lag time to length of pipe run???
    Link below is for a device I have been using for 4 years. It doesn't speed up hot water but it does reduce water waste by recirculating the cold water until it reaches hot then shuts itself off. By using remotes one just has to click the remote a minute or so before using hot water. It can be installed by user without a lot of technical complications.

    http://tinyurl.com/ycgfh4y

    Rob

  12. #27
    DIY Member MikeQ's Avatar
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    Default Space issues

    Quote Originally Posted by philp View Post

    We chose tankless because we wanted the extra space (I can build a home theatre in my basement now!) but I wouldn't recommend tankless to anyone who doesn't have a space issue.
    In many cases a tankless heater can be located closer to the main points of use than a tank could. This is particularly true with electric tankless since there is no exhaust to consider. Moving a water heater closer to the most common points of use is the single best thing that can be done for convenience and efficiency. My 28kW electric water heater is not much larger than a VCR and it can certainly crank out large and endless amounts of hot water.

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