Radiant heating flow slow

[bn friend]

I just bought a house with radiant heat in New York the system runs off a Takagi propane open hot water heater. There are 2 manifolds with 2 pumps running with 1/2 pex piping.
The system works fine if one pump runs, but if two pumps run the flow rate is very slow.
I feel the pumps are not the problem from my research I believe the layout of the piping from the heater is the problem.
There is no circulation loop before the manifolds. What I need is someone to help or hire to redesign the system. Trying to save money and DIY this project.
Any suggestion would greatly appreciate the info.
Thank you
John

 

[fitter30]

Take some pics of boiler, piping and pumps. Model of boiler, brand and model of pumps?
Pex have any idea of feet per loop and how many loops?

 

[PoorUB]

The system works fine if one pump runs, but if two pumps run the flow rate is very slow.

Something has to be plumbed wrong so the pumps are fighting each other.

When you say two pumps, does each manifold have it's own pump?

IMO, there should be a primary loop with one pump on it sized for the boiler/water heater. Then two tees from this that branch out to the two heating zones or secondary loops. The heating zones can have one pump for each zone, or one pump and zone valves like the picture. in the picture flow through the water heater/boiler is downward, and flow through the loops is upward. The piping from and round aback to the boiler needs to be large enough to handle all the water flow the boiler will need, even through the tees.

Similar to this,

 

[bn friend]

Take some pics of boiler, piping and pumps. Model of boiler, brand and model of pumps?
Pex have any idea of feet per loop and how many loops?

The heater is Takagi T-H3 S-DV-P each manifold uses 2- Grundros 15-55 SF pump 3 speed The first manifold has has 5 loops 1/2 pex about 250' runs. The second manifold has 3 loops 1/2 pex with 250' runs.
The heater is an open system sharing house hot water with floor heating. The temp is 120 degrees when running water return is about 110 temp. House water has mixing valve for temp adjustment. Pipe size on hot side feed from heater is 3/4 feeding both pumps after the pumps pipe is 1'' to manifolds. Each pump feeds the separate manifolds. The return water from manifolds are 1'' pipes the connect to 1 1/4'' pipe back to the heater and reduce to 3/4 fitting into the heater. Please see photos

 

[fitter30]

Piped wrong look at post 2 piping pic. Boiler piping common piping the red and blue lines from boiler the two tees should will be piped back to back. Not like yours is. Does the boiler have a pump in it? Don't know model of boiler. Also check valves are piped wrong. Water 1 jpeg. take a pic higher and couple back a little so we can see the whole picture.

 

[bn friend]

Piped wrong look at post 2 piping pic. Boiler piping common piping the red and blue lines from boiler the two tees should will be piped back to back. Not like yours is. Does the boiler have a pump in it? Don't know model of boiler. Also check valves are piped wrong. Water 1 jpeg. take a pic higher and couple back a little so we can see the whole picture.

I understand its piped wrong. I don't know for sure if the heater has a pump but believe it does not. Attached are more pics. The check valves are going with the flow of water, are you referring to the lower check valve that feeds hot water?
There is allso 2 check valves that return cold water.
If i make a primary loop what size pump and size pipes are needed? where can i get a diagram to follow? Are the pumps that feed the manifolds correct?

 

[fitter30]

250' = 8000 btu's per loop
250' = 7.5 ft of head since loops are piped in parallel each zone is the same head
40k btu for the 5 loops, 24k for the 3 loops 1 gpm - 10k btu's + 3' head for piping
When running one pump it heats have you tried just running the other pump by itself?
There in a inlet water filter in the heaters piping page 49. Page 38 cleaning the hx.
Service manual

https://www.google.com/url?q=https://www.takagi.com/media/47718/240-340-540-TH3J-TH3S-TH3-Installation-Manual-68A161-2.pdf&sa=U&ved=2ahUKEwir1om6j5aKAxVkrYkEHblfB28QFnoECBAQAg&usg=AOvVaw1YJ1FygPtvCS-EvlmSlbXA

https://www.tanklessking.com/mwdownloads/download/link/id/899/

 

[PoorUB]

IMO, the pumps does not have enough head for that heater. I would want a minimum of 10 feet of head at 8 GPM, and probably more. Maybe someone else has an opinion on this. I might want a higher head pump for the floor loops too, but beings you have them, I would run them.

What screws it up for me it is a water heater, designed for 8 GPM, and probably a 50 degrees rise. With floor heat you will never have 50 degree rise, maybe 20 degrees. Typically, a boiler, (not a water heater) that will do 200,000 BTU you will need a 20 GPM pump. I don't think you can ram 20 GPM though this unit and you won't have the temp rise with it any way. So you deal with the 8 GPM, 20 degree rise and the water heater barely runs.

 

[PoorUB]

Any suggestion would greatly appreciate the info.
Thank you

I looked over the pictures you posted, and yes, it is really screwed up! Thar water heater is pretty restrictive for flow, and then the floors loops are to. Your big "choke point" is the water heater, plus the same pump(s) are doing the floor loops too. Your flow drops when both pumps run because of the water heater has the most restriction to flow, and with both pumps they are fighting it.
I would rip most of it our and rebuild it like the picture in post #3. Use one pump you have to circulate through the heater, and the other to feed the floor loops and add zone valves to the floor manifold to control them separately. The pumps you have might be enough to do the job, but they are right on the edge. They will pump 8 GPM at a bit better than 10 feet of head on high speed. One pump should be enough to feed both floor manifolds.

 

[bn friend]

250' = 8000 btu's per loop
250' = 7.5 ft of head since loops are piped in parallel each zone is the same head
40k btu for the 5 loops, 24k for the 3 loops 1 gpm - 10k btu's + 3' head for piping
When running one pump it heats have you tried just running the other pump by itself?
There in a inlet water filter in the heaters piping page 49. Page 38 cleaning the hx.
Service manual

https://www.google.com/url?q=https://www.takagi.com/media/47718/240-340-540-TH3J-TH3S-TH3-Installation-Manual-68A161-2.pdf&sa=U&ved=2ahUKEwir1om6j5aKAxVkrYkEHblfB28QFnoECBAQAg&usg=AOvVaw1YJ1FygPtvCS-EvlmSlbXA

https://www.tanklessking.com/mwdownloads/download/link/id/899/

Thanks for the info when running one zone and one pump heat works fine. When running two pumps heat works but flow slows down. The fitter on the water heater is not clogged i have checked that last week.
How to set up a primary loop? What is the best way to set up?

 

[PoorUB]

Primary loop is simple. Just imagine a pipe running from the outlet of the water heater, back to the inlet, with a pump in there somewhere. There is your primary loop.
Now add two tees to the primary loop. The one closest to the outlet of the boiler goes to your floor loop pump, or secondary loop, on the supply side, the other the is the return from your floor. Put them side by side on the primary loop.

 

[bn friend]

Primary loop is simple. Just imagine a pipe running from the outlet of the water heater, back to the inlet, with a pump in there somewhere. There is your primary loop.
Now add two tees to the primary loop. The one closest to the outlet of the boiler goes to your floor loop pump, or secondary loop, on the supply side, the other the is the return from your floor. Put them side by side on the primary loop.

If i understand hot water out run pump then first tee to the manifolds, Second tee get any return from manifold. The straight pipe goes back to cold water to heater. Do i need any check valves? What size pipe should be used for primary loop? i attached a plan where would domestic hot water and cold water feed be added? Any other parts that would be needed?

 

[PoorUB]

If i understand hot water out run pump then first tee to the manifolds, Second tee get any return from manifold. The straight pipe goes back to cold water to heater. Do i need any check valves? What size pipe should be used for primary loop? i attached a plan where would domestic hot water and cold water feed be added? Any other parts that would be needed?

I think you have the idea. As for pipe size, Taco recommends 1" copper. you should not need any check valves.

Domestic hot water? I don't see that in the pics. I thought this was just for floor heat! Or do you mean the water refill line?

 

[bn friend]

I think you have the idea. As for pipe size, Taco recommends 1" copper. you should not need any check valves.

Domestic hot water? I don't see that in the pics. I thought this was just for floor heat! Or do you mean the water refill line?

Pic 5 to the left runs to a mixing vale from the hot side for house water

 

[PoorUB]

Pic 5 to the left runs to a mixing vale from the hot side for house water

Do you have a controller the kills the floor heat when you need domestic hot water?

I assume you have a water tank with a heat exchanger for domestic hot water.

 

[bn friend]

Do you have a controller the kills the floor heat when you need domestic hot water?

I assume you have a water tank with a heat exchanger for domestic hot water.

NO controller for domestic water no water tank or heat exchanger. When hot water is used it goes to the house first never lacks water flow.

 

[PoorUB]

NO controller for domestic water no water tank or heat exchanger. When hot water is used it goes to the house first never lacks water flow.

So the same water that heats your floor can end up in your domestic hot water?!

 

[bn friend]

So the same water that heats your floor can end up in your domestic hot water?!

yes

 

[Fav Onefour]

So the same water that heats your floor can end up in your domestic hot water?!

I wondered the exact same thing.
Seems crazy and I figured I had to be wrong.

 

[PoorUB]

I wondered the exact same thing.
Seems crazy and I figured I had to be wrong.

If that is how it is plumbed, it is against code, and potentially dangerous! Your floor heat doesn't run all summer and water can stagnant in the floor. Then in the fall you fire up the floor heat and that stagnant water mixes in with you domestic water. Very bad deal!

There needs to be a "side arm" water tank with a heat exchanger installed, or some other heat exchanger to separate the floor heat loops from your domestic water.

 

[Firebrick43]

If that is how it is plumbed, it is against code, and potentially dangerous! You floor heat does run all summer and water can stagnant in the floor. Then in the fall you fire ip the floor heat and that stagnant water mixes in with you domestic water. Very bad deal!

There needs to be a "side arm" water tank with a heat exchanger installed, or some other heat exchto separate the floor heat loops fro your domestic water.

Plus it brings in constant oxygen to destroy the system as well

 

[dscheidt]

yes

This is how you grow legionella pneumophila. Everything about this system is wrong. rip it out, start over.

 

[bn friend]

This is how you grow legionella pneumophila. Everything about this system is wrong. rip it out, start over.

Can you send my a schematic diagram of the correct set up?

 

[PoorUB]

It gets complicated. Running floor heat and domestic hot water from the same boiler can be done, but it is tricky. One issue is you want high temps for the heat exchanger for domestic water, 150F minimum. Floor heat all you need is 120F and often the tuning is not rated for high temps. Then, can the boiler, (water heater in this case) even do what you need to do?
First glance you are looking at a mixing valve, or a some sort of mixing control to run two temperatures. Usually, some sort of priority controller is necessary so the floor heat is shut off when their is a call for domestic hot water.

To be honest, I probably could make it work myself, but telling someone how to do it is a bit more than I am comfortable over the internet. Perhaps someone else would like to step in.

Either way, you have a mess. Adding the domestic water really creates an issue. If it were simply floor heat it would be easier.

 

[kj_mustang]

If it is a true water heater and not a boiler, I would add a large enough plate heat exchanger to use for the radiant loops and isolate that water flow from the domestic water. Flow would be something like, water heater to primary loop of pipe that has the home domestic supply and the supply and return piping to the heat exchanger tee'd off it. Would need a pump on the supply pipe to the heat exchanger controlled by heating call from thermostat and zone controller. Return water to heater from primary loop and would need a cold water supply for domestic usage make up. Secondary loop for radiant heat that uses the heat exchanger as heat source and pump/controller for flow. Depending on water temperature out of the heat exchanger, you may need a water mixing valve to mix floor loop return water to hot supply water to get it down to targeted floor loop temps.