Domestic hot water heat exchanger

[markmudd]

This has probably been covered before, but any opinions on what works for some of you all out there concerning what size copper heat exch coil and how l many feet in length is needed in my non pressurized tank to give good domestic hot water perfomance. The domestic water supply will be flowing through the coils. 50 lbs of pressure max.

Is 60 feet enough length? Would 3/4 line splitting off into two 1/2 copper coils, each 60 ft long, then returning to 3/4 size be better than 60' of 3/4 copper? 60 ft of 3/4 is cheaper than 2 -1/2' rolls. Assume 1/2 inch would do better with heat transfer? With expense of copper, hoping to keep price reasonable .

My 450 gallon tank in winter runs 150 to 180 degrees and in summer with solar draindown system may only be 130 or so at times.

I will be using a tempering valve. A local heating guy around here says with our water they are constantly malfunctioning and said don't even use one. How much trouble are they to keep working?

Thanks for the advice.

 

[dswitham]

I took a 100' coil of 5/8" refrigeration copper tubing, slid it over a tank that we had and shaped it in to a coil. I got the copper from www.coppertubingsales.com. They were great to work. Then we made a hanger that hangs over the side of our tank and holds the coil in the top part of the tank. I still get hot enough water to take a shower with when the tank gets down to 128 or so in the top. We have not ever run out of hot water, even with four showers in a row. I even turned the mixing valve down to about 100 and used straight hot water to fill our hot tub, all 450 gallons of it, and didn't run out of hot water. Our incoming water is extremely cold, usually 34-36 in the winter, and I was worried that the coil wouldn't do it, but it has worked wonderfully. My favorite part was turning off the breakers to the hot water heater.

 

[Fred61]

I have two 100 foot coils of 3/4 inch copper running parallel in my 500 gallon unpressurized tank and I took my shower this morning with the top of the tank temperature down to 132 degrees. There was probably a couple showers left in the tank! I ran the two coils instead of one 200 foot coil because I figured it would reduce the head pressure.

BTW, are there fittings to connect 5/8 refrigeration copper to standard water copper tubing?

 

[dswitham]

BTW, are there fittings to connect 5/8 refrigeration copper to standard water copper tubing?

We just used 1/2" fittings standard fittings.

 

[markmudd]

Any pressure or volume issues reducing down to 1/2 " from 3/4" then back going back to 3/4" I should be concerned about if I use the smaller diameter copper tubing? Presently the hot water heater is 3/4" supply and return. I would think 1/2" line of 140 to 170 degree water hot water would be sufficent for most domestic hot water needs and the 1/2 line would get better heat transfer from storage?

 

[dswitham]

I haven't noticed any pressure change between using the coil we have now versus the hot water heater. It didn't seem to change our pressure going from 3/4" to the smaller diameter coil and then back to 3/4".

 

[markmudd]

thanks for your input guys. I'm thinking I will use 120 ft of 1/2 " copper.

 

[jebatty]

I would think 1/2†line of 140 to 170 degree water hot water would be sufficent for most domestic hot water needs ...

I would urge you not to supply domestic hot water at these temps - very dangerous - a disastrous injury just waiting to happen.

 

[Hunderliggur]

Tempering valve s are for safety - anti scalding. If you have water so bad it fouls a tempering valve treat your water. With a conventional DHW you can set the temp and forget it, no need for a valve. With storage HX your hotwater water supply temp could be almost anything. Temper it.

 

[DaveBP]

A local heating guy around here says with our water they are constantly malfunctioning and said don’t even use one.

Yeah, after hanging around our local brake and muffler shop I noticed that they are constantly malfunctioning. So I took the brakes and mufflers off my vehicles to save all that bother and expense.

 

[juddspaintballs]

You could plumb up your own tempering "valve" using a gate valve on the cold side coupled with a spring check valve (to prevent hot water flowing into cold) and a gate valve on the hot side coupled with a spring check valve (to prevent cold water flowing into hot). You're basically making a faucet that feeds the house with hot water. Manually control the temperature by gating the hot and cold waters to safe temperatures.

 

[markmudd]

I couldn't agree more with safety issues. The question was not whether or not to use tempering valve. Please see initial post. I would also agree the heating /air guy is a knuckle head for the record! Question was how much do tempering valves malfunction? plug up whatever? I have no experience with them and never had a need for one until now. I assumed it could be done manually. Seems like a manual set up would require frequent adjustment especially during summer with solar system? The solar and wood boiler system were just installed in November. I expect the solar panel will put out a lot of hot water when weather warms up, but I'm not sure what kind of tank temp I will be able to achieve and how much it will vary. Hopefully I can maintain at least 130 degree water thru most of summer for my domestic hot water needs? I'm certainly anxious to see how the solar system will work.