Do I need another pump

Seiler2k

I bought my house 15 years ago and it uses hydronic heat. It has base board radiators in the second level, radiant heat in a slab on the main floor, and two blower units in the basement. I recently had to replace the manifold to the radiant heat system due to leaks and not being able to find parts for it. Now that it is installed, the temperature in the radiant system is too hot. The system uses a 4-way mixing valve to control the temperature of the radiant system.

The question I have is if the radiant system needs its own pump? Currently the whole system only uses the one pump. But now when I open the mixing valve enough to get any flow in the radiant loops, the temp goes to 140F. I am assuming I will need to install another circulating pump in the radiant loop, but can someone tell me how to determine what size pump to use? I don't know capacity or distance of the loops.

Also I don't have a lot of room to work with between the mixing valve and the manifold. Any restrictions on how close the pump can be to either of these components?

Thanks for any help you might be able to give me.

Jamie Hall

You may not need another pump -- but you may need a different thermostatically controlled mixing valve. An important question, though, is how is the whole thing piped? Can you draw a diagram showing the piping and pump and valves?

Seiler2k

A simplified drawing for you

Seiler2k

Seiler2k

Alan (California Radiant) Forbes

Yes, you will need another pump at the mixed outlet side of the 4-way mixing valve. If the radiant loops are within specification, i.e.
Less than 300 feet of 1/2" tubing or
Less than 250 feet of 3/8" tubing,
a Grundfos 15-58FC 3-speed circulator would be my choice.


As far as piping considerations, try to have at least 10 pipe diameters of straight pipe on the suction side of the circulator. That is, if you are using 1" pipe, have 10" of straight pipe leading to the circ. You may have to be creative.

hot_rod

You need a motor actuator on that 4 way valve also, to make it work as intended. Did it have a motor or actuator on it at one time?

4 way valves were common in the cast iron boiler days as they could provide mix down and boiler protection. Also an outdoor reset function. But they need an actuator and control to do that.
In the drawing Alan showed, notice the motor on the valve and sensor at the boiler return, and low temperature supply.

Seiler2k

hot_rod said:

You need a motor actuator on that 4 way valve also, to make it work as intended. Did it have a motor or actuator on it at one time?

Valve is manual. Looking at someday getting a motorized one that monitors the outdoor temp, but not in the cards right now. Already spent over 1000 this month.

Seiler2k

After talking with the wife, I think we are going to order a taco 4 way mixing valve with the outdoor reset function. I hate spending the money, but if I have to solder pipe I might as well as do the mixing valve now and just be done with it.

Current question is I'm going to have to make a couple of turns in my return line to get the new pump in place (bought a Grundfos 15-58FC like recommended). Is this going to be an issue if I do a tight 180 back towards the manifold?
Rough idea below.

Seiler2k

Thanks for the help I have gotten so far. I appreciate it greatly.

Can someone advise me on the size of the mixing valve I need to order. The old one that is installed now (picture above in previous post) looks to be 1 1/4" with 1" bushings in it. All of the piping is 1". Do I gain something with the larger valve? Is it worth buying the larger valve just run smaller lines to it?

Thanks again

Jamie Hall

The U bend won't give any more resistance than two elbows anywhere else. Not to worry.

Pick the valve size according to the rated flow. Going bigger is not necessarily better. It depends on flow.

Seiler2k

Jamie Hall said:

Pick the valve size according to the rated flow. Going bigger is not necessarily better. It depends on flow.

@Jamie Hall Thanks for the response. I inherited this system when I bought the house. I don't know what the actual flow is. If all the pipes leading to the valve are only one inch, would I gain anything even if the rated flow through the valve was higher?

The CV for both the 1 inch and the 1 1/4 inch are both listed as 9.3. In fact the stats are almost all the same between the two valves. So based on this I am assuming I am not gaining anything by going up to the 1 1/4 valve. Let me know if I am missing something, otherwise I will order the valve in a day or so.

Thanks again!

Seiler2k

Reading through all the posts again, I noticed that I have planned to put my recirculating pump on the return side of the radient system, but the picture posted above by @Alan(CaliforniaRadiant)Forbes shows it in the supply side pulling from the valve and pushing into the manifold. Am I OK on the return side? Do I need to change my plan to the supply side?

Thanks one more time

Jamie Hall

If the pump is on the return side of the piping, you may have problems with low pressure at the inlet to the pump -- which can destroy a pump remarkably quickly. The less piping you can manage between the system expansion tank and any pump inlets, the happier things will be.

Alan (California Radiant) Forbes

As far as sizing the mixing valve, how big is your main floor in square feet and how many loops are there on the manifold? A picture of the manifold will help.

hot_rod

1" is fine. It's probably the same valve, just different port size if they both are 9 Cv.

Seiler2k

I finally got my mixing valve in as it was back ordered for quite a while. I am posting a picture of my roughed up pluming setup. Anyone see any issues before I solder it up? 12 inches from mixing valve to pump, 1 inch pipe. Thanks for looking at this for me.
Reminder that this is just rough layout and pipes will be trimmed to be parallel. Also not final placement of transformer. This is looking up at ceiling of the room. Thanks again

hot_rod

Maybe take a shot showing more piping

Seiler2k

I can in a bit, but I just want to confirm pump placement. 

Seiler2k

Picture of manifold, not yet hooked up. Had to move to get the 10 inches of straight pipe before the pump I am adding. 
Picture of mixing valve

Fill valve is directly underneath the boiler supply, in case that looks weird.

hot_rod

Piping and pump is correct
What type of boiler? You may need a pump
on the boiler loop if it has some pressure drop?

Ironman

Where's the return path from the manifold to the system?

Seiler2k

hot_rod said:

Piping and pump is correct
What type of boiler? You may need a pump
on the boiler loop if it has some pressure drop?

There is already a pump on the boiler loop. At one time the entire system was driven with this one pump. Somehow it worked. But I had to replace the manifold due to leaks and then couldn't get flow through the old mixing valve with out the temperature being way to high. That's why I am adding the pump and electronic mixing valve to the radiant loop.

Ironman said:

Where's the return path from the manifold to the system?

It runs parallel to the supply line. It enters the mixing valve opposite the boiler supply.

Ironman

Okay, it's a 4 way valve. I didn't see the forth port at first.