Pump Size

BCook

I apologies ahead of time for the long question. I'm trying to change out my pump with one that is calculated correctly.

I have a Taco 007e 2F2 with max 16GPM and 10ft head. I get between .2 and .3 GPM on the flow gauges at the manifold. Using a thermal scope I can see that the lines only show heat half way through the floor before the thermostat call off. I'm burning more LP than I should.

I have a 1000SF garage, 15FT ceiling with 1000LF of 1/2" PEX 12" on center in a 5" slab wrapped in 2" Poly Bd. I calculated heat load at 42,000 BTU. I calculated the Temp drop at 20 degrees. My pump feeds a 4 zone manifold to 4ea 250ft lines. I calculated 4GPM for flow.

This is where I start to lose it. I think my pressure drop is 0.375/10ft making the ft head 0.0375. I think I multiply .0375 x the 250ft line.

Can someone get me back on track and help me get over the finish line.

Thanks in advance.

EBEBRATT-Ed

based on the above

If your head is 0.375/foot @4gpm then 0.375 x 250 would be your head=9.375'

BUT

Is 4gpm your total flow meaning 1 gpm for each loop? It must be because you can't get 4gpm through 1/2" pex

Assuming you need 1 gpm flow in each 250' loop your head is .4'/10' of pex

so 250/10=25 25 x .4=10' of head

At least that is what I came up with.

EdTheHeaterMan

9.375 or 10 ft head is within the pump's performance range. at 4 GPM the pump should be able to ramp up to 10 Ft heat. Since that is not working for you, you must have other factors that are not considered.

• How far is the distance from the outlet of the pump to the manifold?
• What size is that pipe?
• How far is the return manifold to the inlet of the pump?
• What size is that pipe?
• Are you including the amount of all the pipes from the closely spaced teed on a P/S system?
• If not P/S are you including the pressure drop through the heat source? (boiler or heat exchanger)
• Are there any other devices that will cause a pressure drop like balancing valves (or zone valves that don't have actuator motors) that may be included in the manifold, or even a flow check valve or a mixing valve. 

Add up all those as parts of the total equivalent length of the system that the pump must feed, and you may be over the Maximum 10 ft head that 007e is capable of providing.

If, for example, you have a system with a total head of 12½ feet, and you need to pump 4 gallons per minute through that system, the Taco 007e is not powerful enough for that system.   

To paraphrase Chief Brody: "We're gonna' need a bigger PUMP" is appropriate for this conversation.

hot_rod

I think your load is kinda high? 1000 sq ft with a 42,000 btu/ hr load is 42 btu/ sq ft

I would guess the load is 1/2 that? Where is this located?

BCook

EBEBRATT,

Yes Sir, I figured 4gpm at the pump and 1gpm in the lines. I understand and agree with your calculations.

EdTheHeaterMan,

• How far is the distance from the outlet of the pump to the manifold? =3ft
• What size is that pipe? = 3/4"
• How far is the return manifold to the inlet of the pump? = 11ft
• What size is that pipe? = 3/4"
• Are you including the amount of all the pipes from the closely spaced teed on a P/S system? There is an additional 3ft of 3/4 from the y that continues to the mixing valve.
• If not P/S are you including the pressure drop through the heat source? (boiler or heat exchanger) I'm using a Noritz NRC98 Tankless Heater in LP. Their graph shows a pressure loss of around 8psi at 4GPM.
• Are there any other devices that will cause a pressure drop like balancing valves (or zone valves that don't have actuator motors) that may be included in the manifold, or even a flow check valve or a mixing valve. I have a Taco mixing valve w/Max. Variation in Supply Pressure: 20%.
• The ever hot manifold has the flow adjusters on top. I have them open all the way.

Hot Rod,

I used the calculator on calculator.net. Is there another way to calculate? The garage has a 15 foot ceiling and the temp difference is only 2 degrees in it's present configuration. The building is located in northern Virginia. The highest point of the system is about 10 feet AFF at the air eliminator.

I'll work on getting a picture if that helps.

Thanks again.

LRCCBJ

Their graph shows a pressure loss of around 8psi at 4GPM.

………..ahh…………that's 18.4 feet………….all by itself. I'd be surprised if it would flow 2.5 GPM with that pump.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1825814#Comment_1825814

my. 730 sq ft, 15’ tall shop, one 12x12 overhead door, shop near salt lake, 5 degree design day has a load right at 15,000 btu/hr. 6” walls, 12” this with 1” spray foam everywhere then fiberglass batts over the foam.

General rule of thumb is .65 gpm for 1/2” 300’ pex loops that keeps the circulator a reasonable size

this is a very simple easy to use spread sheet load calc.
Another favorite with a free demo is at www.hydronicpros.com It is a windows program only.

https://www.pprbd.org/File/ByAlias/HeatLossCalcXL

GroundUp

You'll never get 1 GPM through a 250ft loop of 1/2" PEX with a standard sized circulator. Usually .8 per loop is about the best you're going to see, but .6 is more realistic especially if the fluid is cool. Would I be correct in assuming you don't have primary/secondary piping and are trying to use a tankless water heater as a space heating appliance? If that's the case, that's your problem as tankless WH have a tremendous amount of resistance to flow. Also, like Bob said above, your heat load is almost certainly far lower than calculated.

hot_rod

1 gpm in a 250 foot loop, 1/2 loop is around 9.4'

In a 300' loop around 11'

This is the pressure drop just for the loops.

This free PPI calculator allows you to plug in other components, valves, fittings, etc.

Screenshot 2024-12-09 at 4.10.20 PM.png

If the actual load is smaller, then you are back at the .5- .65 gpm per loop number

Ironman

I'm using a Noritz NRC98 Tankless Heater in LP. Their graph shows a pressure loss of around 8psi at 4GPM.

This is your problem. A tankless water heater has far too much resistance to flow and is not designed for space heating.

Use the right tool for the job: a boiler.

BCook

Thanks for the great advice!

This is important information I should have included. This is a closed system with 40% glycol. In the picture below, ignore the heater on the left. That will be for separate shop sink.

Thank you for all the great advice. I'll recalculate and see what I come up with.

hot_rod

while not the ideal heat source, many of them get forced into submission to pretend to be a heating boiler.

Years ago there was a fellow on this list that built an interface box for tankless mods. I don’t see him or the box around anymore.

Kaos

That pump is too small. It is enough on its own to feed your floor heat loop but doesn't have enough head for the boiler as well.

You can use two of them in series to boost up the overall pressure capability or swap out for a 009. The two in series is probably the cheaper option.

No need for the mixing valve, the only time you need one is if there are zones that need different temperature water. Set the tankless for the temp you need and let it run. This will also save you some extra pressure loss.

GroundUp

As has been stated, you're using the wrong appliance. They can be made to work decent, but not piped like this. At the very least, you need to remove the mixing valve and convert it to primary/secondary piping with a high head circulator (such as an 009) on the tankless loop. Then your floor loops will do what they need to do, independently from the tankless loop

Ironman

Here’s a simple diagram of p/s. I’d use a Grundfos ups26-99 to pump the heater.

Also, 40% glycol is not needed in N. VA. I’m in Shenandoah Valley and we only run 35%, even up in the mountains here. 40% is pretty thick and harder to pump.

BCook

Learning from mistakes is how you earn what you learn…..unless you're packin parachutes. There is a lot of food for thought here and I'm appreciating the education. Back to the drawing board I go. 😎

Ironman

Also, the height of the water column doesn’t matter as far as pump sizing in a closed loop. It only matters concerning the static fill pressure which is needed to lift the column of water. .433 psi will lift a column of water one foot.

Kaos

P/S piping is not the solution to every problem. In case of a tankless unit, it is rarely the right solution.

The OP does not have a system with condensation issues or zoning or even different temps. This is a simple single zone floor heat setup. A single right sized pump (or two smaller one in series) feeding the zone without a mixing valve is all that is need.

BCook

The mixing valve goes away today. Without precon advice, in my mind I thought I could get more efficiency by mixing return water with the supply. I think I get it now. Is there a preference between pumping to or from the heater on the primary loop?

GGross

https://forum.heatinghelp.com/discussion/comment/1826169#Comment_1826169

The primary issue that needs solving is flow, which p/s will definitely solve

GGross

https://forum.heatinghelp.com/discussion/comment/1826234#Comment_1826234

draw up a quick sketch of what you are thinking. Generally I would puut the pump pumping towards the source of pressure drop, in this case on the return pumping into the heater.

EBEBRATT-Ed

Too much glycol. 30% is all you need. Plus the resistance of the heater is the real problem. I agree pump towards the largest resistance .

BCook

This is what I'm thinking.

Kaos

https://forum.heatinghelp.com/discussion/comment/1826239#Comment_1826239

So will a larger pump. No need to replumb anything, just install the larger pump.

For P/S, depending on loop flow rates you can have a couple of modes of operations

Primary flow above emitter flow:

-you are sending part of the heated water back to the inlet of the tankless unit, depending on the temps and the unit, they don't like this and can throw an error. Also RWT is higher so efficiency is a bit less.

Primary flow bellow emitter flow:

-you are essentially mixing down the hot water by the return water from the emitters so your emiters get colder water, need to crank the SWT to compensate.

Primary flow equal emitter flow:

-perfect, all heated water is sent to the emitters and the coldest possible water returned to the tankless

In case of the equal flow, there is zero flow through the closed coupled T, which operates the same as if there was no P/S loop. From experience, I can tell you the balanced operation is hard to get right, but hey, welcome to try it yourself.

I would pipe as a single loop with larger pump (or two pumps in series) and call it a day.

P.S. Single loop with two pumps in series is exactly the same operation as the balanced P/S setup.