Calling All Plumbers

[Chilly807]

With my system the make-up water supply serves two functions. It replaces any water that is "lost" for whatever reason. Secondly, it maintains the system pressure at about 15 psi.

I don't have a traditional boiler, but a geo-thermal heat pump. Having said that, the "heated water" side of the system is pretty much the same regardless of what type of heat source you use. The temperature and flow rates may vary from type to type, but the components are generally the same.

I use in-floor piping for a heat exchanger, and individual zone pumps to circulate the water, plus a central circ pump to move water through the heat pump and storage tank when it's running.

The Spirovent is mounted at the top of the system, which is where trapped air will go as it circulates. I've never had any issues with trapped air so it must be working. My water temp is relatively low (about 90* F max) by design, although it's adjusted by the outdoor temperature sensor as the outside temp drops or rises.

If you're getting too high a water temp through localized heating, the water can begin to boil, which will generate steam in the system and cause problems too. It may be as simple as increasing the water pressure slightly to increase the boiling point or boosting the pump flow through the heating coils to improve heat transfer.

All my pumps are variable flow (manually set) to fine tune the flow rates as required. In general, your zone pumps (if you have them) should be pressure fed from the main circ pump, otherwise they will cavitate if the flow rate through the main pump isn't high enough. i.e. if you have two zone pumps both demanding water at 2 gpm, and your main pump is supplying it at 3 gpm you have a problem. A single circ pump and several zone valves will eliminate that problem, but there are advantages to setting it up either way.

Sean

 

[kidr]

Here's the answer he wants......Rectorseal makes the boiler sealant that you're looking for. Make sure you use plenty.

 

[kidr]

Oh...and don't thank me ........my pleasure

 

[jimgerken]

I still stand with "your expansion tank is too small". Double it (or add a second one).

 

[rScotty]

,.... Having said that, the "heated water" side of the system is pretty much the same regardless of what type of heat source you use. The temperature and flow rates may vary from type to type, but the components are generally the same.
Sean

I'm new to the thread and Sean's post caught my eye. At first I was going to point out how similar our systems are....and then realized that although some components are the same the resulting system comes out very different. There are lots of nice things about hydronic heating. I had to live with it to even begin to understand how different it is. Now I'd never go back to heating with scorched air.

What is really similar about Sean's system and mine is that we have both come up with systems that use larger quantities of low temperature water. Don't know how Sean decided to do that, but one day as I was calculating just what I'd need for a boiler....it suddenly hit me that I didn't need a boiler with it's small quanitity of high temperature water at all. In fact, all I'm buying by going that way is fast response and higher losses. If I was willing to put up with slower response - that is, maintain a very level temperature all winter then what that type of hydronic heating system really needs is a large amount of warm water. Not a little bit of hot water.....It needs more heat, not more temperature. And going that way would allow the system to be completely sealed. No more problems with make up water....

So my system is totally sealed: no makeup water at all. In fact, no real water at all. It runs on a propylene glycol solution which eliminates freezing and corrosion issues. It's now 5 years old and hasn't gained or lost any fluid.

This morning it is 18 F outside, about 72 inside, and the system is running at 15 psi and 125 degrees F. The heat source it uses is a standard hot water heater. The heated fluid is pumped via one smallish circulator pump to pressurize eight zones. There are hand valves balance the zones or fine tune them, and thermostats working motor-driven valves to turn each zone on or off. Heat is exchanged in two ways: via pex pipes directly buried in concrete floors for about half the system, and via rau panels directly under the hardwood floors for the main room and kitchen. Back by the heat source there is a spirovent and two expansion tanks.

We didn't plan to heat the house with this system, but temperatures get very cold here and we wanted an inexpensive supplemental heating system that would be completely reliable for keeping the house warm if we decided to go somewhere else. You know...to take a break from old man Winter. To my surprise, that hot water heater ended up easily heating the house most of the time. If it gets really cold out (below zero) this system will still keep the house livable, but it's more comfortable - and more efficient - to fire up the wood stove.
rScotty

 

[quicksandfarmer]

With my system the make-up water supply serves two functions. It replaces any water that is "lost" for whatever reason. Secondly, it maintains the system pressure at about 15 psi.

If the pressure release valve and expansion tank are working properly they should maintain system pressure inside an acceptable range for the full range of operating temperatures.

If your system can't maintain pressure without make-up water, it's leaking.

Leaking is bad. It leads to shorter boiler life.

 

[rScotty]

I still stand with "your expansion tank is too small". Double it (or add a second one).

Yep. That's what I did; I added a second expansion tank. Sure wish I'd found one made of something other than painted rustable steel though.

It's easy enough to figure out what you need in the way of expansion tanks. Just figure out how much fluid you have and what the fluid temperature range is and what kind of volume change will result from the heat. Use the coefficient of thermal expansion that has the same units for your way of measuring volume and temperature.

Like Jim said, the easy & conservative way to take care of the fluid expansion is to put in enough expansion tank capacity to take care of the extra volume. It doesn't hurt to have extra capacity.

The non-conservative but seriously engineering geeky way would be to assume that the storage tank and the piping is also going to expand right along with the heated fluid - although probably not at the same rate. But There's a lot of piping and it's on the outside, so it has the advantage of geometry. Maybe, just maybe, there is enough expansion in the tank and pipes that we can do without a dedicated expansion tank. The problems start when we start solving this kind of problem. First off we figure that something might be constraining some of the pipe (it might be concrete). And the storage tank itself has to have some kind of rigid wall. But the dang temperature varies because of the thickness of the constraining concrete or of the shell of the tank or whatever. That's bound to be the case with any well-insulated tank or with pipes buried in concrete floors. Now we suddenly find ourselves needing a differential equation to solve the basic volume problem and that's even without considering the added system pressure, and any change in altitude, or the time it takes the whole system to heat up....all of which combine to make just adding an extra ugly expansion tank an awfully lot more attractive solution.
rScotty

 

[Chilly807]

I'm new to the thread and Sean's post caught my eye. At first I was going to point out how similar our systems are....and then realized that although some components are the same the resulting system comes out very different. There are lots of nice things about hydronic heating. I had to live with it to even begin to understand how different it is. Now I'd never go back to heating with scorched air.

What is really similar about Sean's system and mine is that we have both come up with systems that use larger quantities of low temperature water. Don't know how Sean decided to do that,

Mine was more through necessity than anything else. The geo-thermal is capable of producing high temperature water, but the best efficiency is obtained if you keep the output water under 100*F. An oil-fired boiler is easily capable of producing very hot water unless you have a phenomonal flow rate through the heat exchanger. That's why most oil fired systems have mixing valves, to bring the output temperature down to a reasonable level. Geo-thermal isn't well-suited to baseboard heat exchangers, the water temp simply isn't high enough for good heat output.

Heating a concrete slab is another thing, however. The hottest my slab temp gets is about 85-90 *F, about the same as the palm of your hand. I've had folks come in for the first time, start walking around in their sock feet, and be disappointed because the floor doesn't "feel warm". A visit to the garage, which isn't normally heated, soon opens their eyes as to what warm and cold feels like.
The more efficient the house is in retaining heat the lower the water temperature you need with in-floor piping. My boiler control has an input for outside air temp, it will automatically scale the water target temperature based on how cold it is outside. It also monitors the floor slab temp to keep it warm through sunny winter days when the sun streaming in through windows warms the house and would otherwise allow the slab to cool off too much.

One of the downsides to in-floor heating is the slow response to heat input or loss, it takes a few hours to change the slab temperature an appreciable amount.

Ok, I'll not hijack this thread any more, we were talking about entrained air, weren't we ??

Sean

 

[nuffer460]

I have had this problem with a two year old system. It's now 15 years old. The heating company that put it in, could not figure out the air problem. Just on a whim, I replaced the pressure releif valve. If I don't replace the valve every two years. I get a cavitation in the water lines. I haven't had another issue, as long as I replace the pressure releif valves. Hope this helps!! The water fall sound every time the pumps came on drove me nuts.

 

[johndeerezach]

yes that spiro vent should do it my dad is a plumber of twenty some years and i also am but go school also. you need to put that vent at the highest point of your boiler lines(going to boiler) and that will take all the air out. hope it helps