Boiler and zone draining questions

[notmyrealuser]

Hello,

New here, but I have been lurking for a while while planning a remodel. I am not a plumber but consider myself handy and love to learn. Good info on here and I will probably be posting many questions, thanks in advance for info and help!!

I have a Slant Fin GG-125H from 1983 and 4 zones. It's set up with one main circulation pump for 4 zones. The pump resides under a man made copper manifold, and each zone returns into that manifold via a zone valve. There is a shut off valve on the return side but not on the supply side. There is a drain valve for each zone above the manifold and the boiler and piping is the lowest spot in the house. I am confused about how the supply side works. It appears that a zone gets turned on, the zone valve opens and the pump pushes cold water from that zone into the boiler, and the the supply line gets hot. I only see one supply line headed out into the crawl space so how does the new hot water stay only in the zone that turned on? I'm going to have to chase some pipes and I'm new(ish) to this house so maybe I am missing something.

I need to drain 1 zone to make some remodeling possible. I am removing baseboards to move a wall etc. so I need to drain so I can cut the copper out and re-position. I want to keep the other three zones available while I do this as it will take some time and nights are getting chilly. Can I simply turn off the thermostat on that zone, hook a hose up to the drain valve and empty it? Or do I need to shut all the valves on the return side of the other zones? And then opposite, do I just refill at the drain valve and shut don the valve once the zone is full? Thanks Newbie!!!

 

[Plumber69]

what a mess

 

[Sponsor]

 

[Dana]

OK, so it's not a thing of beauty...

To be able to turn off a zone you need to turn off isolating valves on both the supply and return of that zone. It's hard to sort out from the pictures which valves those would be.

Even derated for altitude the output of the Slant Fin GG-125H is more than 2x oversized for normal sized houses. Most boiler that's 35 years old are ripe for replacement- won't hit their nameplate AFUE numbers even when sized correctly, and at 3x+ oversizing they're over the knee of the curve, with high enough idling losses to be quite a bit lower efficiency than their steady-state efficiency. It's worth running a fuel-use based load calculation, and start thinking about what the right replacement equipment would be.

The amount of radiation per zone also affects the as-used efficiency. With 4 zones and an oversized boiler it's likely to be short-cycling whenever just a single zone is calling for heat. A right sized modulating condensing boiler might be able to handle the zoning much better. The napkin math on that bit of analysis can be found here.

 

[notmyrealuser]

Thanks for the replay. A new boiler is something we plan on doing in the next couple years. Every year I get the back-flow tested and have this boiler serviced they always say it is running fine and no signs of anything to worry about.

So I fear there is only a shut off valve on the return of each zone, I can see them all in the back (reaching them is another story). Would it just be easier to drain the whole thing a refill it? I only have about 30 minutes worth of pipe work and then I can refill it.

Thanks!

 

[Dana]

Thanks for the replay. A new boiler is something we plan on doing in the next couple years. Every year I get the back-flow tested and have this boiler serviced they always say it is running fine and no signs of anything to worry about.

So I fear there is only a shut off valve on the return of each zone, I can see them all in the back (reaching them is another story). Would it just be easier to drain the whole thing a refill it? I only have about 30 minutes worth of pipe work and then I can refill it.

Thanks!

Sure, you could drain the whole thing, and star in the lead role the "Joys of Air Purging". If the zone valves are on the supply side and don't leak you may get lucky and be able to drain just the zone you're working on.

When you replace the boiler with something more right-sized and efficient it's probably worth trading in that water heater for an indirect fired water heater running as the "priority zone" off the boiler. Don't up-size the boiler just because it has the hot water load- size the boiler for the space heating load, and the water heater for the largest tub you have to fill. Even the smaller boilers can deliver more hot water than the burner on a typical 50 gallon standalone, and at higher net efficiency too.

Derated for 6000' of elevation using standard formulas the GG-125H delivers about 80,000 BTU/hr, which is enough to heat about 4000 square feet of 2x4/R13 type house at your ~+10F 99% outside design temperatures, and would usually be overkill for anything smaller than ~2800'. With four zones it's almost surely short-cycling on zone calls which cuts into efficiency even more than the excessive standby losses. With a modulating lower-mass boiler more appropriately sized for th heat load it will cut the fuel use pretty significantly- more than would be apparent than from simply comparing the AFUE efficiency numbers.

 

[notmyrealuser]

Since I do not know the joys of air purging personally, I gave it whirl and drained the zone I need to work on. I cut and moved pipes in the crawl space and refilled the zone. All zone are heating, no leaks, and I don't hear anything abnormal. I did open the air purge valve on the farthest baseboard of the zone I cut into and a tiny bit of air came out then steady stream of water. How do I know if I have air in the zone?

Thank you for advice. And I need to refer back to your notes on the boiler when we are ready. I am plumbing the floor for radiant heat and we may have the option of also heating our driveway (that's damn expensive though) so I want the right system just in case.

 

[notmyrealuser]

Bringing this back to the top. First, thanks for the advice my system is working off the old boiler and all the air is out of the system. Pretty easy job once it was all done, although I am not totally done with my remodel yet, and i do have some issues now that it is operational.

I have 4 zones total each having its own set of baseboard heaters and thermostats. My zone 1 was the baseboards in the kitchen and living room controlled by its own thermostat. For my remodel I tore out all of the baseboards in zone 1 and replaced with radiant pex loops and installed a manifold. The manifold is tied into the supply and return that once fed the baseboards for that zone. Everything is working, no air no leaks, and the radiant heat is awesome!! Now to my issue....

The supply temp hitting the manifold is at the top end of the threshold for the manifold and pex specs ~190F, and 20 degrees less on the return side. The floor feels fine even at its hottest when its been on a long time.

How can I turn down the supply temp from this old beast? Or do I need to use a mixing valve, and if so where can I pull cooler water from? It is a closed system with a back-flow preventer. Do my baseboards in the other rooms even need to be that high of a supply temp? I know there are some calculations that need to happen to answer the efficiency question, but after I am done next month the entire lower level will be on radiant loops except two carpeted bedrooms with baseboards.

Thanks in advance everyone!

 

[Dana]

The supply temp hitting the manifold is at the top end of the threshold for the manifold and pex specs ~190F, and 20 degrees less on the return side. The floor feels fine even at its hottest when its been on a long time.

How can I turn down the supply temp from this old beast? Or do I need to use a mixing valve, and if so where can I pull cooler water from? It is a closed system with a back-flow preventer. Do my baseboards in the other rooms even need to be that high of a supply temp? I know there are some calculations that need to happen to answer the efficiency question, but after I am done next month the entire lower level will be on radiant loops except two carpeted bedrooms with baseboards.

Thanks in advance everyone!

See the diagram on the right side of p2 of the manual, where it reads "WATER TEMPERATURE CONTROL". The newer ones use a smart temperature controller, different vintages will have used aquastats, but the aquastat well where the boiler temperature is sensed probably hasn't changed locations, so that's roughly where it should be.

One question is how long and how frequent are the burns when serving just one zone? If the burns are significantly shorter than 5 minutes or more than 5 burns per hour it's worth hacking in a heat purging economizer to work with the available thermal mass for lengthening the burns and lowering the total number of burns per hour/day/year. The Hydrostat 3200 shipped in the newer versions clearly works, and has a programmable Thermal Pre Purge function that should help if it's short-cycling. The Intellicon HW+ is usually pretty easy for DIY installation too.

 

[notmyrealuser]

Thanks Dana. To be honest, I downloaded that last night and never even saw that on page two, whoops... Hopefully the adjustment is self explanatory, as IIRC there is a Honeywell device in that location that all the zone valves are connected to.... I'll take a look.

The boiler is short cycling close to the 5 minute mark. I'll take a look at the two devices and the prices. This boiler is getting replaced in the next year so I don't want to throw a ton of money at it unless it has an ROI or can be used effectively on a new boiler.