zones, pumps, and air bubbles

[dyihomer]

Hi,

We have a house that uses a boiler and basebords for heating, it has 5 zones, and a 1/25 hp circulation pump (the house is around 3000 sqft). Every time the heat starts up, we can hear popping noises.
The other day we called a plumber comes to fix the noise in the baseboards, saying that the noise is from air bubbles. So he bled the system and guaranteed that he could remove all the air and the the heating wouldn't make popping noises anymore because it will be completely filled with water and no air. A few days later, the heating was still making the noises (a bit less than before but still loud), so we called him back, this time he says that we need to buy an additional part to filter out the air bubbles, and additionally there's steam making noise because the hot water is moving too slowly because our pump is smaller than it should be and doesn't have the power to move the water. And after asking some more questions, he says that the steam is like air making noise, and that because the house is big and has 5 zones, the elbows will trap air inside that we can't get out without buying a filter and a larger pump. So, he wants to replace the pump we currently have with one that is about 1.5-2cu ft in size and he wants to add a filter, saying that he guarantees that the noises will stop after replacing both parts.
However, the pump in our house was replaced less than a year ago, by a different plumber. That plumber said that the circulation pump he installed is the right size for this size of house.
Since we don't know much about plumbing we are lost as to what actually needs to be fixed and how to do it!

Any suggestions or advice will be greatly appreciated!

BTW, both plumbers are licensed and have been in business more than 10 years.

 

[Jadnashua]

A closed hot water system normally should have an air extraction device. There are various versions on the market. But, once that air is out of the system, since it is supposed to be a closed system, new air getting in is the result of leaks, either water or air. If the system needs to add water, that new water will have a little air trapped in it. If during an off cycle of the boiler, because the pipes and water contract some as they cool, if there is a leak anywhere, it can suck in some air. A leaking bladder tank could introduce air into your system (until it became fully waterlogged, then you'd have other problems - high pressure cutout is the most likely, along with temperature and pressure relief valve leaking).

So, look for water leaks. Check any and all valves for evidence of leaks. Consider adding an air extraction system (one is called Spirovent, but there are others, that may work better, I just haven't researched that).

 

[Sponsor]

 

[Plumber1]

air

I would pay attention to what Jim said and

if it were mine, I would have an automatic Maid-o-Mist type vent on the boiler, and I would set up each zone so it could be purged with a hose. That would take out all of the air and keep the system free of gurgles. Too much air in a zone and suddenly no heat.

If set up properly, you could get rid of the noise in ten or fifteen min.

 

[dyihomer]

Each zone does have a place I can hook up a hose to bleed the system. Previously, the plumber bled all five zones, but it's still making noise so an air extraction device might be handy. How would I know if we have an expansion tank or bladder tank? And which air extraction device is known to work best?

Lastly, how about the size of the circulation pump... is it ok for the house and the number of zones or should we change it too?

 

[Jadnashua]

An expansion tank usually is a bladder tank. The tank has air on one side separated by the bladder. Water is on the other side. The air side can be pressurized with a tire pump (and it should be set to about the normal pressure of the water system - often around 15 pounds on a hot water boiler). The water expands when heated into the tank, compressing the air. When things cool off again, the air pressure pushes the water back into the main line, keeping everything from having excessive pressure, or creating a vacuum. Depending on the amount of water in your system, it is probably a tank about a foot in diameter and maybe 1-2 feet long. It would need to be somewhere (typically but not necessarily) near the boiler on the closed (heat loop) water line.

 

[hj]

pump

That pump may be extremely undersized for the system you have, but we would have to see its performance curve to verify it, along with some information about your system.

 

[dyihomer]

so what size circulation pump would be best for a house with 5 zones and that is around 3000-3500 sq ft?

 

[Jadnashua]

Each situation will determine what best is. SOrry, you need to know how many gallons/minute you need to transfer the necessary heat, how many feet of radiators, the heat load (this depends on the insulation, the windows, and the maximum temperature difference between outside and inside, and the prevailing wind, and the exposure), the diameter of the pipes, the length of the loops, how many floors (how high it must pump), and the number of changes of angles.

The thing that can be measured or calculated is the head pressure. Then, you can look at the characteristics of each pump to match your needs. Manufacturers publish flow characteristics of their pumps with flow on one axis and head pressure on the other. The more head pressure (friction) there is in a loop, the fewer gallons/minute on the same pump. Also, there is a maximum velocity that can be used otherwise you get cavitation (air) in the pipe. This can be quite destructive and noisy.

So, sorry, at least I can't tell you what pump to use.

If you go to one of the pump manufacturer's websites, you can look at their charts and see what a pump would do, but you also need to know what your head pressure is and how many gallons per minute are required to actually move enough hot water around to get everything hot enough to keep the house warm.

Take a look at the pump you have, check the brand, then the model number. Go to that company's website and see what it actually is capable of. The water velocity is important to keep within limits...the smaller the pipe, the slower you want the water to go or you erode the pipe (but this limits how much heat can be transferred); plus a smaller pipe will flow fewer gallons per minute even with the same pump because it will generate more head pressure than a larger pipe.

It is a series of compromises and tradeoffs. Sometimes, if you only have one circulator, and have radically different potential loads, if you choose a pump that can handle the worst case load, it may be trying to pump way too much water for the system if only one loop is calling for heat. You can have bypasses, but that can make things more complicated. Or, you can use a smaller pump and have more than one (say one for each loop). Then, it can be sized for the specific needs of that loop...longer loop, potentially a bigger pump.

It isn't a one size fits all. A home in Florida the same size as yours would not need much heat, but the same house in Michigan in the middle of winter would need huge amounts.

Assuming your house has properly designed radiators and piping, for your area, there may be an ideal pump. What that is, can be figured out, or should have been, by the person that designed it.