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Old 06-07-2010, 10:49 PM   #16
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low domestic hot water flow with tankless coil


Mineral deposits will both restrict the water flow and result in a drastic lowering of output temperature as you turn the water on higher. The minerals insulate the domestic water from the boiler water and in effect reduce the gallons per minute versus temperature rise heating capacity.

On some furnaces the tankless works worse in summer because the circulator (that sends FHW to the radiators) is not churning the boiler water about the tankless.

If you are lucky, the mineral deposits are not adhering to the tankless coil so alternately tapping the tankless unit (removed fromt he furnace) and flushing backwards with a garden hose might dislodge it all.

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Last edited by AllanJ; 06-07-2010 at 10:59 PM.
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Old 06-08-2010, 12:00 PM   #17
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low domestic hot water flow with tankless coil


I was planning to drain my boiler, cut the domestic coil input/output pipes, and just replace the whole coil or flush it somehow, but a friend who does maintenance for apartment complexes warned me to never remove the coil because it may never go back in properly and could leak. Is there any truth to this? He probably works on 20yr old equipment while my boiler is ~3yrs old.

I'm learning towards doing an electric water heater, by the way.
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Old 06-08-2010, 01:41 PM   #18
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low domestic hot water flow with tankless coil


On older boilers. You can have trouble with a leak if you don't take some precautions.

As for going back in right. Only a problem on some larger coils(as in 10 GPM and larger).

For what you can save in oil. The cost of switching to electric is well worth it.
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Old 06-08-2010, 02:18 PM   #19
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low domestic hot water flow with tankless coil


okay I have another question... my water report says total dissolved solids is 375mg/L, which is very hard. I don't mind the effects on drinking water, faucets, etc., but it is clearly detrimental to appliances (hot water heaters, dishwasher, laundry machine). Would it be wise to hook up a water softener to the pipe that feeds the water heater, so all hot water is softened? From what I've been reading, even an electric tank heater will be quickly destroyed by hard water.

Of course, this site says that softened water increases corrosion: http://www.waterheaterrescue.com/pag...intenance.html
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Old 06-08-2010, 02:21 PM   #20
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low domestic hot water flow with tankless coil


Best to have the softener piped that it does all the water the house uses.
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Old 08-16-2010, 07:23 PM   #21
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low domestic hot water flow with tankless coil


Figured I'd update this. I bought a 80gallon electric hot water tank heater and a friend and I installed it over a couple beers. Been in a month or two months now and its an amazing difference. I actually get real water pressure now, no regrets at all. The boiler will just be used for winter heating of radiators now. I completely understand what the inside of the coil must look like, too. I got rid of my old drip coffee maker and started boiling water in a pot to use a french press. The water pot gets caked in minerals after only a couple uses. With the amount of water flowing through that coil for a few years I'm not surprised at all that it is clogged to hell. Thanks for all the advice.
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Old 08-16-2010, 08:17 PM   #22
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low domestic hot water flow with tankless coil


Thanks for the update.
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Old 09-16-2010, 01:05 PM   #23
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low domestic hot water flow with tankless coil


I have an old system with a hot coil and i installed the little shower head that saves water. Its a little stainless steel water saving shower head. It slows the water flow which gives a slow pass through the coil with hotter water. I also up the temp. in winter and lower in summer.
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Old 10-29-2010, 12:21 PM   #24
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low domestic hot water flow with tankless coil


Same setup as original post i.e. oil fired boiler/baseboard heat/tankless coil (all 20+ yr old). Problem is we only get a short duration shot of hot water delivered at same rate/pressure as the cold water(around 40#). Plumber installed a new tempering valve which seems to work since the temperature of the shot of hot water changes w/ adjustment of the tempering valve. Tried cranking the house thermostat up til the heat came on and water was circulating thru the baseboards, but this had no effect on the water from the tankless coil. Water supply is New Hampshire well water so probably pretty hard, but if flow is not an issue, seems to me that the coil should not be clogged. Bottom line, normal hot water pressure to faucets but only a quick shot of heated water at whatever temp the tempering valve is set for. Any suggestions would be welcomed.
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Old 10-29-2010, 02:39 PM   #25
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low domestic hot water flow with tankless coil


May not be clogged. But it can still be insulated from the minerals.
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Old 11-01-2010, 12:43 PM   #26
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low domestic hot water flow with tankless coil


Is there a possiblity it's a bad or wrongly set aquastat?
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Old 11-01-2010, 04:02 PM   #27
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low domestic hot water flow with tankless coil


Is the low limit set below 160?

Its very common for a coil to become insulated.
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Old 11-24-2011, 08:17 AM   #28
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low domestic hot water flow with tankless coil


I have the same issues - oil boiler with domestic coil. What worked last time, when the hot shower quickly turned to lukewarm, was having the coil cleaned. Oil company says the coil probably needs cleaning every 5 years or so due to such hard water, so that timing is right as the problem returned. I am holding off the cleaning as it is about $200, and if I turn up the house heat the domestic stays hot from the boiler.

I've not bought an electric water heater because when the boiler dies I would like to switch to natural gas overall. But then maybe an electric water heater now may make sense if I can turn off the boiler in summer and save on a tank of oil (that I use over the summer) which is about $800. Actually, I guess that one summer's oil would pay for the tank. Then, I like the endless hot water from the coil for long steamy showers.

I've not added a whole house water softner due to adding salt to the water and any health concerns. Not keen on adding any chemical in drinking water. I have filters for both kitchen faucet and also shower (that removes chlorine) both from Aquasana. My washer was replaced when I bought the house as it broke but I realized also that the hot water was plugged up. Had my new washer now for about 5 years and no issues (yet). Additional concern for water heater is if it bursts - it would be in the basement - and flood is a concern. I recall when I lived in NH that there was such super hard water, and everyone's water heater in the condo complex was bursting at 3 to 5 years which surprised all of us. I moved to NJ so did not do anything to resolve the situation in NH, and the hard water here in NJ seems a bit more tame.

Last edited by Netmouse; 11-24-2011 at 08:23 AM.
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Old 11-24-2011, 08:35 AM   #29
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low domestic hot water flow with tankless coil


Quote:
Originally Posted by beenthere View Post
Cooking out the coil. Is a time and material job. Could take an hour and a half. Or it could take several hours. As in 4 or more.

An electric water heater, is often cheaper to use for hot water then a tankless coil in a boiler. Almost always.

You can then set your boilers min temp to a much lower temp after you install an electric water heater.
yes it sure is did this for my son ...really saving ...great point beenthere......

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