water flow direction for air bleed valves on hydronic baseboard

confusedHO

Should the air bleed valve be located on the inlet side or the outlet side of a baseboard unit?
Does it really matter? Will the air bleed valve work on either side?

EBEBRATT-Ed

There usually put on the return. If you vent with the circulator off it won't make much difference (if the BB is level) With the circ. running they sometimes don't vent real well depending on the velocity of the water passing by the 1/8" tapping in the baseboard elbow.

confusedHO

EBEBRATT-ED: Are you saying that with the circulator running it won't vent real well regardless of where the air bleed valve is, or it won't vent real well if it is on the inlet vs on the return?

Isn't bleeding air out just a matter of checking for air at each baseboard in the loop and then doing it again. If the baseboard is level and if the air has risen to the baseboard it should come out either end, right?

Jamie Hall

confusedHO said:

EBEBRATT-ED: Are you saying that with the circulator running it won't vent real well regardless of where the air bleed valve is, or it won't vent real well if it is on the inlet vs on the return?

Isn't bleeding air out just a matter of checking for air at each baseboard in the loop and then doing it again. If the baseboard is level and if the air has risen to the baseboard it should come out either end, right?

It may not vent really well if it is on the feed end.

As for "just a matter of checking..." it would be nice to think so. Doesn't work that way. Air bubbles get carried along with the flow. Now one does do an initial bleed with the pumps off and the pressure raised -- but the air bubbles in the piping don't just rise to the top. Takes time and patience...

Paul48

If it's series loop baseboard, set it up so you can power purge it. What you're saying is how it "should" work. It rarely does though.

EBEBRATT-Ed

Ok now we know it's a series loop. The power purge will get rid of most all of the air. Any air left in the system because it is a loop (and you should have plenty of water velocity) will get carried back to your boiler. You can vent it there with whatever means was installed to vent air, manual vent, compression type expansion tank, auto air vent, air scoop-whatever you have.

If there is Any air remaining in the baseboard you can try venting the baseboard. The vents on the baseboard to me have limited use on a series loop with a power purge, just my opinion. If installed they should be on the return as the water will push the air in that direction. If installed on the wrong end and the system is already filled I wouldn't drain and move them unless you absolutely can't get the air out of the baseboard

confusedHO

Again I have shown that I am indeed a ‘confused homeowner’. I have been doing a “power purge” all along for my system without knowing the term. I thought it was just my system design that demanded this ‘drain and forced refill’ and that everyone else just uses the air vents! I will definitely make sure that the new boiler has the power purge capability.

Yes, I have a series loop with 5 baseboard units. The reason that I asked about the air vents is because the new boiler will be in a new location and I may want to change the direction of the water flow. I had the impression that it would be a very bad idea but now I think maybe not.

Thank you both for your help.

icesailor

Being old and foolish, I never bothered with the worry of which direction the water was flowing in a series looped baseboard system. It had to be really old, and installed way back in the last century, so there was almost always some way to purge the system. Back during the last century, after venting all those emitters, after taking painted end caps and trying to vent the air, I ended up purging the air anyway. So why bother? What difference does it make? When I install air vents, even though I didn't use them, their locations had more to due with the location in a room. What I might have to move as furniture to get at the vent. That I was never going to touch, ever again in my life.

It doesn't really matter as long as you purge it properly. And have the means to do so.

Paul Pollets

It also matters that the circulator pump is pumping on the supply header away from the location of the expansion tank.

confusedHO

Thank you, Paul. I read that pumping away from the expansion tank is important. That is how my current system is and I will make sure that the new system is done that way also.

confusedHO

After looking at boilers again I realize that I spoke too soon on my last comment.

I am looking at 85% efficient conventional cast iron boilers using propane. The boiler I am looking at, Burnham ESC3, has the circulator pump built in. In this configuration the circulator pump will be pumping on the supply header toward the expansion tank which is the opposite direction that you and others have stated is the correct way to do an installation.

How do you handle this situation? Do you fix this by replacing the circulator pump in the boiler with regular pipe and moving the circulator pump further out the supply line to just after the expansion tank? Would this void any warranty? Do you automatically disqualify the boiler because they put the circulator pump inside?

See http://inspectapedia.com/heat/Circulator_Pump_Installation.htm Their answer to the question ”Where to Mount the Circulator Pump on a Heating Boiler?” is
“Read the instructions: The short answer is, mount the circulator and arrange all other piping and controls according to the boiler manufacturer's installation and operating instructions and you won't go wrong.”

Do you believe that “you won’t go wrong”?

Paul48

Yeah...Can't go wrong....If all else fails, read the directions http://s3.supplyhouse.com/product_files/ESC3-install.pdf

SWEI

confusedHO said:

I am looking at 85% efficient conventional cast iron boilers using propane.

If you are still looking and are burning LPG, I would strongly suggest you look at a modulating condensing boiler instead. The apparent 10% difference you see when comparing AFUE ratings does not reflect that actual fuel savings from a properly sized, installed, and commissioned mod/con. Depending on the specifics, you could be looking at anywhere from 20 to 30% less fuel per year IME.

icesailor

Paul Pollets said:

It also matters that the circulator pump is pumping on the supply header away from the location of the expansion tank.

Well over 90% of anything I touched had the circulators mounted on the returns.

If anything, purging systems with circulators on the supply could be a PITA because I always purged with the boiler running and hot. So, if not careful, one could get cavitation in a supply side circulator and make steam/air.

confusedHO

Sorry I haven't responded. I was away.

I was wrong about the ESC3. The circulator is not built into the boiler. I am planning on mounting it on the supply side.

icesailor: I will read up on purging and being careful to not get cavitation.

SWEI: A modulating condensing boiler is most efficient running at lower temperatures. I will be running my baseboards at 170° to 190°F so the conventional cast iron will suit my purpose just fine.

SWEI

confusedHO said:

A modulating condensing boiler is most efficient running at lower temperatures. I will be running my baseboards at 170° to 190°F

On the coldest days of the year.

Do you actually LIKE giving money to your LPG company?