Need some pointers to increase flow on my Hydronic floor system.

johnjs

I tried doing as much research as possible to figure my issue out prior to making a post, but I just can't seem to solve this on my own. I put this system together in 2020 when I did some renovations on my house.

It consists of a Takagi hot water on demand with three taco 0015 pumps. One Primary and one for each zone. There are two zones with two manifolds. One zone and manifold is for the first floor and one zone and manifold is for the second floor. The manifolds are located on their respective floors. On my first floor I have (5) 1/2in 300ft loops and on the second floor I have 3 300ft loops.

The system works, and maintains my home's temperature better than you might expect, its been working for four years, however I suspect there is room for fine tuning and improvement. Recently, I noticed the hot water heater was only displaying .7GPM for flow. That's what led me down the rabbit hole, then i started checking my manifolds and noticed only 1 or two of the loops had the proper return temp, and the other loops returns were staying somewhat cold. I also noticed on the flow gauges on the loops, the flow was so low it wasn't really even registering in the site glass. I dont have individual loop thermometers, however over all, on both manifolds, the supply is going in at 120 and the return was barely breaking 80.

I know these answers can get very mathematical and complicated as I learned when doing research. I am not that advanced in this area so I am going based off the very basic knowledge I have.

From what I've read, as a very general rule of thumb, 0.6 gpm per 300ft loop is a good starting point. If that were the case, I should be looking for something around 4.8GPM. I've reviewed the manual for my hot water heater, and it is more than capable of this. It's a takagi T-H3S-DV-N.

I thought it could possibly be a speed issue on the pump, but I played around with the speeds and it had a miniscule effect on the gpm displayed on the heater. I then thought maybe it developed some air bubbles and needs to be bled. This is where it gets interesting. I started bleeding it, and was going to each manifold and closing all the loops and opening one at a time, No real air to speak of. I went back to the hot water heater and stopped the bleeding process. When i went to turn off the water supply I turned the hot out valve on the bottom of the heater by mistake and then opened it right back up. All of a sudden the gpm shot up to 2.0. I left it a while in disbelief thinking it would settle and come back down to the .6 but it never did. Now I am getting a flow reading on the manifolds and the floors seem to be working much better than they were. The flow reading on the manifold is around .2GPM per loop.

This leaves me with the question, what am I missing that is preventing the GPM from going up to where it needs to be so I can achieve adequate flow for all the loops? The system pressure is at around 20PSI as of now. The loops that were not getting hot on the return seemed like they got hot to the middle of that loop and then just fell off in the middle. I thought it was a balancing issue and that I needed to restrict the other zones, but now that I'm digging deeper into this, I just think I don't have enough flow to push the hot water through all the loops completely. Maybe there's more air? Maybe I am totally off base here and am totally wrong. I'm hoping someone can give me some clarity. I've attached some photos of what I have just for reference. I tried playing around with different pressures in the system also and it seems like the GPM is actually higher around 15-20 psi. I tried making it higher and it seemed to have a negative effect.

Any help or insight is extremely appreciated it.

Thank You!

hot_rod

Have you cleaned out the TY strainer , the device between the white PVC adapters? I'll bet that type, not being a hydronic Y strainer, has a fine mesh inside.

We have also seen a few examples of the media in the Spirovent being partially plugged. It screws apart in the middle.

You have enough isolation valves to easily check both.

johnjs

thank you for the response. I have not checked the y strainer this season however I did clean it mid last season. I can double check it again. I’ve never messed with the spirovent, I will look into that.

Kaos

If I remember correctly there is also a small plastic strainer on the water inlet of the unit. Doesn't take much to clog those up.

Two 0015 is series should get you decent GPM through that unit without issues.

Just making sure, you are not trying to run this as primary/secondary loop.

johnjs

Just making sure, you are not trying to run this as primary/secondary loop.

I’m going to check the strainers, but I’m not entirely sure what you mean by this

Kaos

Tankless units are not boilers. When I tried primary/secondary setup on one, I could not get it to stop cycling with only 1 zone on, return water temps were too close to supply temp making the unit mad. Maybe with a delta T primary circulator it can be made to work but I couldn't with a fixed speed circ.

The other more important issue is a single 0015 has nowhere near enough head to push much flow rate through one unit, maybe 2gpm at the most. Two 0015 in series can get you up to 3-4gpm. If you want primary/secondary setup you need a 009 for the primary pump.

DCContrarian

When I see zero flow I think air in the tubing until proven otherwise.

GroundUp

You're using the wrong appliance, and the wrong equipment for it. An 0015 is inadequate for a tankless WH so you need to upsize the primary circ, and you need to open the purge valve

hot_rod

These charts show the difference in circulator pumps. With a high pressure droop tankless you want a high head type of circ like the 009.

Screenshot 2024-12-08 at 9.48.24 AM.png

Screenshot 2024-12-08 at 9.42.01 AM.png

johnjs

Thanks for all the responses. I checked both strainers today, the one on cold inlet, and the y. Both were completely clogged causing a total restriction. I had cleaned the Y about a year ago, and I live in NY so I havent used the system for 6 months. Apparently I need to check it more often. Cleaned both filters, bled the system and I'm running at 3.0gpm. Definately a huge improvement. My returns are finally at the correct return temp. Thanks for all the help! I will upgrade to the 009 at some point, but for right now, it seems to be working great! I've attached the pics just for reference incase anyone else runs into this issue. Thanks again!

hot_rod

Personally, I would leave that small one out.

If you flush the system, the larger Y strainer is plenty protection. Although it is a tight mesh size for hydronic work. At some point the system should be cleaned of the big particles. A hydronic conditioner helps prevent rust and corrosion also.

johnjs

https://forum.heatinghelp.com/discussion/comment/1825575#Comment_1825575

do you think I can get away just upgrading the primary and leaving the 0015s for the zones? Also, I’m not sure what valve you’re referring to when you say open the purge valve.

https://forum.heatinghelp.com/discussion/comment/1825584#Comment_1825584

Thank you. What’s your opinion on changing just the primary to 009?

hot_rod

if it has worked for 4 years the way it is, I'd leave it.

GroundUp

The brass valve assembly that is supposed to separate the two loops (located about a foot below your zone circs) is a purge tee. With the valve in it closed, you lose hydraulic separation and defeat the whole purpose of this piping arrangement. An 009 or similar on the primary/tankless loop isn't going to do much good with that valve closed because it's still in series with the zone circs unless that valve gets opened. If it's working as-is, probably just leave it but it's definitely not correct.

SuperTech

Why did you install a tankless water heater to do the job that a boiler is designed to do?

Kaos

Thankless and modcon are not the same. A primary/secondary loop is hard to get right on a tankless.

The OP's existing configuration works because that valve is closed. To open that valve and have any hope of getting enough flow would mean replacing the primary 015. Even if you replace the primary 015 with a 009 and open that valve, I would bet it would not work as well as it does right now.

About the only drawback to the current config is some ghost flow through the zone not calling for heat. With floor heat and manifolds, this usually a pretty small flow as the zones are pretty restrictive. In most cases is not an issue and sometimes even preferred as it add a bit of extra load on the tankless without effecting temperature regulation.

This falls into the category that if it ain't broke don't fix it.