Was wondering if this would work to keep hot water at a far faucet, shower. I hate the wait to get water hot. This is a dingle story house with a crawl space. Hot water tank is about 3 feet lower than faucet. Would connect to drain to make circuit. Have always wondered if a passive system like this would work.
Thermosiphon
- Thread starter pugsl
- Start date
It works well in some cases and not that great in others, you need a check valve to prevent water being pulled from the bottom of the tank, you also should plan a way to bleed the air out. I normally do a ball valve, then a check valve, then a tee with a boiler drain, then another ball valve then connect into the tank drain port using a tee so the original drain can still be used. I always leave room to add a circulator in the future if the gravity plan doesn't work. I also highly recommend insulating the pipe, if you don't you are just making a hot water heating loop.
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nadogail
Well-known member
There are systems sold that use a small circulating pump to pull from your hot water line and return to your cold water supply to the heater.
The pump is controlled by a differential thermostat and shuts off when the difference between the hot discharge is less than 7 degrees than the tank temperature.
Typically they are installed under a sink furthest from the water heater. They take their suction from the water line to the faucet and discharge into the cold water line nuder the same sink.
I never bought one because my bride would not give up a space under a sink to install it.
The pump is controlled by a differential thermostat and shuts off when the difference between the hot discharge is less than 7 degrees than the tank temperature.
Typically they are installed under a sink furthest from the water heater. They take their suction from the water line to the faucet and discharge into the cold water line nuder the same sink.
I never bought one because my bride would not give up a space under a sink to install it.
Any recirc setup (pump or passive) will need the lines well-insulated or it will keep cycling the heater.
I put a small HWT under the kitchen sink. Main HWT is right by the master bath. I'm on metered water... can you tell?
I put a small HWT under the kitchen sink. Main HWT is right by the master bath. I'm on metered water... can you tell?
They work great especially if you have a water heater in the basement.
Allows hot water at every faucet in seconds.
Cost all most zero run. The heat loss to operate is almost not measurable witha NG system.
No moving parts, no sensors.
The return line is usually 3-4” below the Insulated supply line return and is NOT insulated.
The last three homes have had the loop with no check valves. One thing if the water heater have “heat saver valve” on the top of the heater they must be removed. Heat savers are usually little flap valve. One of the homes was 100’ long ranch........hot water at every faucet with no wait !!!
There have been several other discussions on the Hot water gravity loop or powered recir in the heating and AC a section
Allows hot water at every faucet in seconds.
Cost all most zero run. The heat loss to operate is almost not measurable witha NG system.
No moving parts, no sensors.
The return line is usually 3-4” below the Insulated supply line return and is NOT insulated.
The last three homes have had the loop with no check valves. One thing if the water heater have “heat saver valve” on the top of the heater they must be removed. Heat savers are usually little flap valve. One of the homes was 100’ long ranch........hot water at every faucet with no wait !!!
There have been several other discussions on the Hot water gravity loop or powered recir in the heating and AC a section
dcg9381
Well-known member
I had a hot water solar system in my last home. It was 100% thermosyphon with no pump. It'll work, assuming the run from the heat source isn't too long.
Look up all the "wood fire" hot tubs on the internet.
Look up all the "wood fire" hot tubs on the internet.
it's a very good way to circulate hot water with no moving parts, no maintenance.
Cost all most zero run. The heat loss to operate is almost not measurable witha NG system.
....
One of the homes was 100’ long ranch........hot water at every faucet with no wait !!!
No NG here. Electric all the way. Prob cost me something extra then.
Rancher too. I think the best I can do is drop the HWT to grade height, which is ~32" below floor level. Do you think it can effectively thermosiphon to faucets/shower 50' away?
Just want to throw a 'real' scenario in here...
larry4406
Well-known member
I did the thermosyphon at a past house. Had 3 levels. Piped the hot in a loop like shown with short branches to each fixture. Insulated the hot line up to the last fixture, then let it go cold without insulation to return (that was the instructions I had at the time, 20+ years ago. Check valve at return at bottom of tank. Worked slick. No pump.
No knowledge on the height requirements .........mine were basement water heater.
Also not sure on the cost as the trade off of running the water for 30 Seconds to minutes to get the hot water to distance faucets vs recirculating system Operation cost. It might be a wash.
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It's acually also called gravity systyem. the hot water is less dense than the cold water & flows up, the cooler water falls . thats what causes the movement.
it works as long as the high popint is higher than the water heater. the higher it is the faster it moves
it works as long as the high popint is higher than the water heater. the higher it is the faster it moves
temps in the attic may affect the flow I think
you need the natural cool down for the system to operate
you need the natural cool down for the system to operate
Innovate1
Well-known member
It may not work at all. These work best if the runs don't have peaks or valleys with the slope always in the same direction.
The constant recirc systems can use a LOT of energy keeping all the pipe hot.
dcg9381
Well-known member
I agree with this. But it doesn't consider the "wife approval" factor.
One way to address it is to make the recirculator "on demand" - meaning on a swtich, or via a remote...
We'll use a recirculating system on or main shower of a home we're building, the main reason is limited water supply.
earl84
Well-known member
Hmm, I always thought this wouldn’t work with a tankless, on demand water heater. It looks like this Taco system that Jeep I linked to actually will. Hmm.
my tankless has a small .5 gallon or so electric fired surge tank it keeps at temp. it has a built in re-circ pump. so I manage to have both recirc and tankless. its glorious. one of the best things i did in the house.
https://www.navieninc.com/products/npe-240a
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agreed. i'd rather get my water from the river, build a fire, heat it, and then use that water to drown in over an electric tankless.