OWB Installation Questions

[Lurch16th]

Just trying to get a handle on some basics.

My OWB comes with a single pump. It will be mounted inside my cellar, well below ground level.

Does the pump need to be at lowest point in whole system, even at, or lower than side arm?

Should the hot OWB water enter the house, through the pump and then to the Sidearm first?
The reason i ask is OWB supply lines are 1", Heat Exchanger for my ductwork connections are 1", but all of sidearm connections are 3/4". If hot water goes to sidearm and reduces down to 3/4", it would have to enlarge back up to 1 " to feed the Heat exchanger.

Or do i simply need a sidearm with1" boiler supply inlets?

Does the hot OWB water have to be pumped from the top - down over the sidearm, while the natural siphon flows upward?
Thought I read that somewhere.

 

[jmcguiretree]

Look up central boilers web site. They show a basic drawing on how to hook up.Good luck

 

[Lurch16th]

Really good diagrams, thanks. Doesn't seem to show what the boiler inlet sizes should be on the sidearm though.

 

[November Wolf]

It will not matter that your side arm has 3/4 fittings. On my CB the fittings at the boiler are 3/4 and from there it goes to 1" pex untill it enters the basement. Then I used 3/4 copper to my heat exchanger. Not problems at all and the 3/4 copper is about the same size as the 1" pex I used.

 

[windthrown]

Yah, as noted above, 1" PEX has an inside diameter about the same size as 3/4" copper. Different standards and ways of measuing the different types of pipe material. So do not worry about there being a 3/4 inch copper fitting size bottleneck in the system. 1" PEX is going to be the main size limit in the sytem, so 1" and 3/4" copper fittings and Hx fittings are not going to reduce your OWB water loop flow.

One point about the pump. I do not know if your OWB is open or pressurized. I hope its open and non-pressurized. At any rate, in a non-pressurized open system, an issue with Taco type OWB pumps is that they tend to cavitate in low pressure systems. Cavitation causes them to fail pretty fast. So to avoid that, you want to place the pump at the lowest level in the OWB water loop, so that hydrostatic pressure is higest in the pump itself. The lower the pump, the higher the water pressure will be there. More pressure, less cavitation, and the pump will last longer. As far as flow goes, the pump will drive the water in the loop wherever it is located.

The OWB loop should be plumbed so that the hottest water goes into the DHW sidearm or Hx first, and then to the house heating unit, be it forced air or hydronic water heating. Plumb the sidearm Hx bottom first, so that the most heat is at the bottom of the hot water convection loop. In water and air, heat rises, so you want the most heat at the bottom of the sidearm. Its the same in flat-plate type installations; put the DHW Hx as low in the DHW convection loop as possible.

 

[Butch(OH)]

The pump does not need to be at the lowest point but best place is there.

Most Mfgs reccomend the side arm being the first unit in line. Cant think of any reason for it other than they want the hottest water at the side arm. Makes sence because mine couldnt keep up with 5 people even when first in line and hot loop temps.

The side arm ports? Cant say for sure, mine were 1" copper on the loop side, 3/4 copper on the domestic side. The boiler loop is going in the bottom of mine and out the top per the instructions that were with it.

 

[Lurch16th]

Very helpful,
yeah, just looked at inside of Pex fitting and sure enough, it's 3/4".

My OWB is a Heatmor 200, semi-open.
So it doesn't look like there is any need to use any pipe or fittings inside the house bigger than 3/4, other than to adapt to existing hardware.

 

[Stihl310]

Yah, as noted above, 1" PEX has an inside diameter about the same size as 3/4" copper. Different standards and ways of measuing the different types of pipe material. So do not worry about there being a 3/4 inch copper fitting size bottleneck in the system. 1" PEX is going to be the main size limit in the sytem, so 1" and 3/4" copper fittings and Hx fittings are not going to reduce your OWB water loop flow.

One point about the pump. I do not know if your OWB is open or pressurized. I hope its open and non-pressurized. At any rate, in a non-pressurized open system, an issue with Taco type OWB pumps is that they tend to cavitate in low pressure systems. Cavitation causes them to fail pretty fast. So to avoid that, you want to place the pump at the lowest level in the OWB water loop, so that hydrostatic pressure is higest in the pump itself. The lower the pump, the higher the water pressure will be there. More pressure, less cavitation, and the pump will last longer. As far as flow goes, the pump will drive the water in the loop wherever it is located.



The OWB loop should be plumbed so that the hottest water goes into the DHW sidearm or Hx first, and then to the house heating unit, be it forced air or hydronic water heating. Plumb the sidearm Hx bottom first, so that the most heat is at the bottom of the hot water convection loop. In water and air, heat rises, so you want the most heat at the bottom of the sidearm. Its the same in flat-plate type installations; put the DHW Hx as low in the DHW convection loop as possible.

I swear people have told me that anytime you mount a pupm at the lowest point in the sys. you then incur all the head pressure from the vertical lift the pump has to create to get it back to the burner... is this not true??? I was mounting mine up on the side of my boiler... about half the guys say yeah thats right, and the other half tell me to mount it in the basement....

I have the 008 Taco pump that I'll be installing, I just want to settle this and figure out where I need to mount it.


Thanks

 

[Lurch16th]

hmmmm, interesting about the pump location.
Never thought about that.

My rough guess is that the only head pressure should exist in any lines or hardwear that is situated higher than the top of the water tank in the furnace. Water should seek it's own level even without the pump, so pressure should be neutral.

So then the only potential problem, should be trapped air.
So the palcing of the pump at the lowest point should be a good thing?

 

[Stihl310]

hmmmm, interesting about the pump location.
Never thought about that.

My rough guess is that the only head pressure should exist in any lines or hardwear that is situated higher than the top of the water tank in the furnace. Water should seek it's own level even without the pump, so pressure should be neutral.

So then the only potential problem, should be trapped air.
So the palcing of the pump at the lowest point should be a good thing?

Thats what my dad and I were talking about, once the lines are full they should be at equillibrium so now i'm thinking the only head pressure I'll see is that from the lines themselves... heck with it, I'll mount it in the basement... if it doesn't work I'll teaer it out and move it.

 

[Slick]

elevation doesn't even enter into the head pressure equation...literally there is an equation and elevation isn't even in it

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

It's a closed loop so whatever you pumping up is falling back down so it doesn't matter....pump head figures in elbows, fittings, pipe size, length, type of pipe etc.

 

[Stihl310]

elevation doesn't even enter into the head pressure equation...literally there is an equation and elevation isn't even in it

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

It's a closed loop so whatever you pumping up is falling back down so it doesn't matter....pump head figures in elbows, fittings, pipe size, length, type of pipe etc.

So woudl this pump head I've been told about only be the case if I were pumping up to the top of a water tower and there was no water on a return line to balance it out... I have hadmore than one person tell me I have to figure in vertical rise into th head pressure

 

[Slick]

yeah i would think if it's a one way trip you would have to figure in elevation pump head. I called taco for help selecting one of my pumps...out of my owb I go up 14ft to an i-beam in the ceiling, across it 40 ft then back down 14 ft then underground 100 ft to my house...I didn't know how to figure in the elevation, figured the fall on the other side would help but didn't think it cancelled it out, tech guy said it cancelled it and sent me that link....elevation doesn't figure in at all if there is a return loop, pump head is all about resistance, fittings etc.

 

[windthrown]

I swear people have told me that anytime you mount a pupm at the lowest point in the sys. you then incur all the head pressure from the vertical lift the pump has to create to get it back to the burner... is this not true??? I was mounting mine up on the side of my boiler... about half the guys say yeah thats right, and the other half tell me to mount it in the basement....

I have the 008 Taco pump that I'll be installing, I just want to settle this and figure out where I need to mount it.

Thanks

Head pressure is not an issue for the pump in a basement. It is actually a benefit to help avoid cavitation, which is the bane of open systems using Taco type pumps. I used a Taco 007 in the ex's CB OWB loop. That is one size smaller than yours. No issues what-so ever. I mounted the pump at the base of the boiler, and the lines run into the attic and down into the utility room. Taco pumps are also used in fully pressurized systems, and that is one of the big selling points of a pressure system: pumps fail less often in them.

I got this information from my old roomate, who is a plumbing contractor specializing in energy systems. He plumbs all kinds of Taco type pumps into heating and cooling systems, and he was the one that gave me the tip about putting the Taco pump as low as possible in the loop. Trust me. It works better that way.

 

[windthrown]

elevation doesn't even enter into the head pressure equation...literally there is an equation and elevation isn't even in it

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

It's a closed loop so whatever you pumping up is falling back down so it doesn't matter....pump head figures in elbows, fittings, pipe size, length, type of pipe etc.

You will always have hydrostatic pressure in the lines with any height of water, open loop, closed loop, in a pond, or otherwise. No way around that. Who was it? Pasteur I think it was used to win money on bets using a small vertical tube of water, connected to wine barrels. Sure enough, every time he filled the little tubes with water to a certain height, the barrels burst. You can have a dam one inch wide and one inch deep, and 100 feet high, and the water pressure at the bottom will be the same as a dam a mile wide and 100 feet high and 100 miles deep.

 

[Slick]

huh? Are you saying the Taco pump head equation is wrong and needs to figure in elevation?

 

[windthrown]

huh? Are you saying the Taco pump head equation is wrong and needs to figure in elevation?

Nope. You do not need to factor for elevation to size the pump. I am saying that you will have more pressure at the bottom of any standing column of water, regardless. Its simple physics. I am talking about static water pressure, AKA: hydrostatic pressure. The pressure is equal on either side of the pump in this situation, and hence these pressure values are not factored for. The hydrostatic pressure will be there if the pump is turned on or not, or if the pump is placed at the lowest location in the line or not. It is a simple function of water column height, and has no dynamic factor. The advantage of this hydrostatic pressure is that air bubbles will not form as readilly as they would if the pump were placed at a higher elevation in the water column. Air bubbles forming in the pump is called cavitation, and cavitation causes pumps to fail.

I am not talking about dynamic pressure, or head pressure caused by laminar flow of water through various sizes of pipes and such, which is what the Taco charts are showing on the web site. They are sizing pumps based on the need to drive the water through a series of pipes. In this situation the pressure is not equal, and the pump has to work to overcome the resistive pressure of water through the pipes.

To reiterate, you can place the pump anywhere in the OWB loop that you like. Hydrostatic pressure will be equal on both sides of the pump at any location. As a result, there is no need to size the pump based on the elevation of the pump in the loop. You can gain benefit by placing the pump at the lowest point in the loop. That will be the place with the highest hydrostatic pressure which will result in less cavitation in the pump. Less cavitation will mean your pump will last longer, as cavitation is one of the leading causes of pump failures in low, or open pressure systems.

Clear enough?

 

[Stihl310]

Nope. You do not need to factor for elevation to size the pump. I am saying that you will have more pressure at the bottom of any standing column of water, regardless. Its simple physics. I am talking about static water pressure, AKA: hydrostatic pressure. The pressure is equal on either side of the pump in this situation, and hence these pressure values are not factored for. The hydrostatic pressure will be there if the pump is turned on or not, or if the pump is placed at the lowest location in the line or not. It is a simple function of water column height, and has no dynamic factor. The advantage of this hydrostatic pressure is that air bubbles will not form as readilly as they would if the pump were placed at a higher elevation in the water column. Air bubbles forming in the pump is called cavitation, and cavitation causes pumps to fail.

I am not talking about dynamic pressure, or head pressure caused by laminar flow of water through various sizes of pipes and such, which is what the Taco charts are showing on the web site. They are sizing pumps based on the need to drive the water through a series of pipes. In this situation the pressure is not equal, and the pump has to work to overcome the resistive pressure of water through the pipes.

To reiterate, you can place the pump anywhere in the OWB loop that you like. Hydrostatic pressure will be equal on both sides of the pump at any location. As a result, there is no need to size the pump based on the elevation of the pump in the loop. You can gain benefit by placing the pump at the lowest point in the loop. That will be the place with the highest hydrostatic pressure which will result in less cavitation in the pump. Less cavitation will mean your pump will last longer, as cavitation is one of the leading causes of pump failures in low, or open pressure systems.

Clear enough?

Thank you for clearing that up, I have heard put it on the boiler, and put it in the basement a millions times... however no one has ever given a solid explanation as to why that is... people have mentioned cavitation but never given a good explanation.

Thanks