[Hydronic Open Loop] No Hot Water Unless Circ Pump On

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HighlandsBoy

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Hi all!

Short-time reader, first-time poster. I just moved into (renting) a Seattle-area townhouse and have realized my heating system is, unfortunately, a hydronic open loop (in-wall forced air radiant) system using a standard hot water tank that is shared with the domestic water system. The owner of the townhouse is not at all mechanically inclined (didn't even know where the water shutoff was on our move-in walkthrough) and had the recirculation pump, which is only connected to the radiant heating PEX loops (ie. not the hot water taps) set to run 24 hours a day which also seems to cause the hot water burner to run 24 hours a day ‍‍(yuck!).

I switched the circ pump to run on timer for only 30 minutes starting at 3am to keep the water in the loops from being stagnant, but, since doing this, I can only get lukewarm water from the tap when the circ pump is off. I've tried adjusting the mixing valve to the hottest setting, but when the pump is off, it doesn't seem to let sufficient flow of hot water into the hot side of the mixing valve. If I close off the valves to the radiant loops, water temp to the taps is hot again. Also, If I run the circ pump, water temp is hot.

My big question is: how can I avoid running the circ pump all summer, keep the lines from becoming stagnant, and have regular hot water to the taps? Also, who thought it was a good idea to design a system like this?! Pic of system below:

highlandsboy-01.jpg
 
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Tughillrzr

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Hi all!

Short-time reader, first-time poster. I just moved into (renting) a Seattle-area townhouse and have realized my heating system is, unfortunately, a hydronic open loop (in-wall forced air radiant) system using a standard hot water tank that is shared with the domestic water system. The owner of the townhouse is not at all mechanically inclined (didn't even know where the water shutoff was on our move-in walkthrough) and had the recirculation pump, which is only connected to the radiant heating PEX loops (ie. not the hot water taps) set to run 24 hours a day which also seems to cause the hot water burner to run 24 hours a day ‍‍(yuck!).

I switched the circ pump to run on timer for only 30 minutes starting at 3am to keep the water in the loops from being stagnant, but, since doing this, I can only get lukewarm water from the tap when the circ pump is off. I've tried adjusting the mixing valve to the hottest setting, but when the pump is off, it doesn't seem to let sufficient flow of hot water into the hot side of the mixing valve. If I close off the valves to the radiant loops, water temp to the taps is hot again. Also, If I run the circ pump, water temp is hot.

My big question is: how can I avoid running the circ pump all summer, keep the lines from becoming stagnant, and have regular hot water to the taps? Also, who thought it was a good idea to design a system like this?! Pic of system below:
Nothing wrong with a direct open loop radiant system. What type radiant heat is it you have??

What are they using mixing valve for ? Hot water tanks run at 120

I make the cold water makeup enter radiant system. that keeps it from being stagnant. No need for circulating pump on a timer.
 

HighlandsBoy

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Nothing wrong with a direct open loop radiant system. What type radiant heat is it you have??

What are they using mixing valve for ? Hot water tanks run at 120

I make the cold water makeup enter radiant system. that keeps it from being stagnant. No need for circulating pump on a timer.

Nothing technically wrong with this type of system except it does open your domestic water supply up to the stagnating water in the radiant loops during the off season. The system is forced air in-wall radiant.

I assume the mixing valve is there to allow you to crank the tank up to 130-140 for the heat/bacteria killing, and still have tap water running sub 120.

That's all besides the point though. My issue is that when I don't run the circulation pump 24/7 in the pictured setup, I can't get more than ~90 degree water from the taps. When I have the pump running I can get 120. Also, when I close the valves to the radiant lines, I can get 120. My theory is that when the pump is not running it starves the mixing valve of hot water which means the taps get tepid water. It's not really my issue to fix being a tenant, but I'm not happy about the high utility bills caused by running a circ pump 24/7, unnecessarily heating the house during the hot summer months, and spiking the gas usage for the water heater.

Am chatting with landlord about it, but he has no idea what the system in his own house is :p
 
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Tughillrzr

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Nothing technically wrong with this type of system except it does open your domestic water supply up to the stagnating water in the radiant loops during the off season. The system is forced air in-wall radiant.

I assume the mixing valve is there to allow you to crank the tank up to 130-140 for the heat/bacteria killing, and still have tap water running sub 120.

That's all besides the point though. My issue is that when I don't run the circulation pump 24/7 in the pictured setup, I can't get more than ~90 degree water from the taps. When I have the pump running I can get 120. Also, when I close the valves to the radiant lines, I can get 120. My theory is that when the pump is running it starves the mixing valve of hot water which means the taps get tepid water. It's not really my issue to fix being a tenant, but I'm not happy about the high utility bills caused by running a circ pump 24/7, unnecessarily heating the house during the hot summer months, and spiking the gas usage for the water heater.

Am chatting with landlord about it, but he has no idea what the system in his own house is :p

If you understood what I described what a direct open loop radiant system was, you would understand that there is no stagnant water if system is correctly done. Every time you turn on the hot tap the cold feeds the system and enters through the radiant with fresh water all year every day. You would also need to use a bronze or ss pump to prevent corrosion. No stagnation! But as you say, that’s besides the point I guess.


Sounds like the mixing valve is used so the hot water tank at its max temp setting ( very inefficient) to provide the hot air in the handler? Then it’s mixed down to 120 for domestic side.

you have a one way valve just above mixing valve indicates the flow of system.
wall unit?
I’m not seeing a relay to turn pump on? You said it was only on 24/7 ? 365?
 

HighlandsBoy

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If you understood what I described what a direct open loop radiant system was, you would understand that there is no stagnant water if system is correctly done. Every time you turn on the hot tap the cold feeds the system and enters through the radiant with fresh water all year every day. You would also need to use a bronze or ss pump to prevent corrosion. No stagnation! But as you say, that’s besides the point I guess.


Sounds like the mixing valve is used so the hot water tank at its max temp setting ( very inefficient) to provide the hot air in the handler? Then it’s mixed down to 120 for domestic side.

you have a one way valve just above mixing valve indicates the flow of system.
wall unit?
I’m not seeing a relay to turn pump on? You said it was only on 24/7 ? 365?


Ya I agree that if correctly done as you describe with cold feeding system there is no risk of stagnant water. Unfortunately this system doesn't seem to be designed that way. The one-way valve above the cold inlet seems to exist to keep the radiant return from feeding the cold inlet of the mixing valve and instead forcing it to go back into the tank. I updated the pipe diagram (below) to show the direction of the radiant flow with the pump on. The circ pump is on a mechanical timer, which the owner previously just had set to run 24/7, but I would only like to run when needed (either by heat needs or occasionally to keep the water from stagnating). Thanks for your input so far!

highlandsboy-02.jpg
 

Fitter30

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Turn pump off, turn return from radiant valve off see if you get hot water. Yellow knob turn ccw to raise temperature. See if the water gets hot.
 

HighlandsBoy

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Turn pump off, turn return from radiant valve off see if you get hot water. Yellow knob turn ccw to raise temperature. See if the water gets hot.

If I turn the pump and return from radiant valve off I do get hot water at the taps. This is what I've been doing, but I'm worried about water stagnating in the radiant loops with the valve shut

Mixing valve is set at maximum temp
 

Fitter30

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Return from radiant valve if there was a check valve installed to the right of the valve flow going towards the valve the pump timer could be programmed to run once or twice a day for 15 minutes.
 

HighlandsBoy

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Interesting. So with the check valve there, cold water would be prevented from flowing back through the radiant loops? Is your thought that cold water is flowing through the loops and mixing with the hot water on the hot water side of the mixing valve when the pump isn't forcing hot water through the lines?
 

Fitter30

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Interesting. So with the check valve there, cold water would be prevented from flowing back through the radiant loops? Is your thought that cold water is flowing through the loops and mixing with the hot water on the hot water side of the mixing valve when the pump isn't forcing hot water through the lines?
When that valve is closed your water temp at faucets was hot. Use a swing check instead of a spring check because of a lower pressure drop.
 

Dana

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Nothing wrong with a direct open loop radiant system.

Except that they don't meet code in most places due to stagnation health risk issues, and where they are legal often require a minimum daily duty cycle to mitigate against said stagnation. It also requires that all valves & fittings & radiation on the heating system meet potable materials standards.

[What are they using mixing valve for ? Hot water tanks run at 120

Huh?

Hot water tanks run at whatever temperature you set them to. It's code in many locations that the installer set the tank to no less than 140F, mixing down to no more than 120F with a tempering valve for water distribution to sinks & bathing taps. (It's OK to send untempered water to dishwashers & clothes washers.)


I make the cold water makeup enter radiant system. that keeps it from being stagnant. No need for circulating pump on a timer.

That would require some reconfiguration of this system, but would probably work (if local code allows it without duty-cycling the flow through the zone radiation).
 

Tughillrzr

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Except that they don't meet code in most places due to stagnation health risk issues, and where they are legal often require a minimum daily duty cycle to mitigate against said stagnation. It also requires that all valves & fittings & radiation on the heating system meet potable materials standards.


**no Kidding did you read all the post ? I guess not!


Huh?


Hot water tanks run at whatever temperature you set them to. It's code in many locations that the installer set the tank to no less than 140F, mixing down to no more than 120F with a tempering valve for water distribution to sinks & bathing taps. (It's OK to send untempered water to dishwashers & clothes washers.)


**i have never seen a code that says hot water tank must be set at 140 and use a mixing valve to lower it to 120. we’re talking about radiant heat 120 is the max ideal temp. That is what makes the use of a hot water tank efficient as per this set up. I understand that you can set one higher but your not gaining anything pertaining to this set up !



That would require some reconfiguration of this system, but would probably work (if local code allows it without duty-cycling the flow through the zone radiation).

**again that’s exactly what I stated and how to prevent that and yes it would involve reconfiguration of piping.

But anymore thoughts lmk!
 

Fitter30

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A black in 1/2" pipe plug in city water will turn into rusty water when the water is first turned on after no flow for a few hours. This hasn't been a problem as stated. Not everybody has building codes in very rural areas.
 
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