Reduce lag time for tankless

Dana said:

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.

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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?

Runs with bison said:

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.

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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

flamefix said:

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

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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.

Runs with bison said:

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.

Click to expand...

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.

Dana said:

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.

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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.

Hot water up 3 floors

philp said:

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???

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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

Space issues

philp said:

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.

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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.