Adding a Zone to a Boiler

[psuce]

Hello all and thanks in advance for any and all help and information. I currently have an old farmhouse with a Thermo-Dynamics boiler. It currently has two zones. One is for the primary part of the house which is heated with nine (9) radiators. The second zone is solely heating the kitchen via a kick-space heater. I had it installed about 20 years ago by a local reputable dealer. I want to break up the main part of the house into two zones (5 & 4 radiators). The dealer wants a small fortune to add an additional zone so I thought I would see what is involved and what my options may be. I have a friend that is a licensed plumber who can more than handle the installation. I am just not sure of his expertise with the design/details of adding a zone. There will be no additional capacity or demand on the system. Just trying to split main part of the house for convenience and control.

As can be seen in the attached photo(s), the supply for both zones comes out of the top of the boiler. The 3/4" supply passes the flow valve and goes to the kitchen which then returns to the right side of the boiler. The 1-1/4" supply (which I want to split) passes the flow valve and then splits to the front and back of the house which then return and merge before going to the circulator. I was wondering if it is as simple as adding another 1-1/4" tee and flow valve coming out of the boiler and plumbing one side of the supply into this valve while leaving the other supply side connected as is. I would then "mirror" the existing setup on the return (left) side adding another circulator for the new zone to the right side using a 1-1/4" tee where existing elbow is connecting the 3/4" return from the kitchen.

As can be seen, there is a bypass on the return side from below the circulator back to the supply side which it is my understanding helps keep the radiators from overheating. I assume I would have to include this in my "mirroring" of the existing setup when installing the new setup.

 

[NY_Rob]

Take a look at this article- it's very helpful and specifically addresses splitting a zone (about half way down the page):
https://heatinghelp.com/systems-help-center/loop-system-hot-water-heating-q-and-a/

Using your existing common return should be fine since it's sized for two returns already. You're splitting one zone into two- so you need to add an additional t-stat for the new zone and each t-stat will control flow to it's zone via a powered zone valve- which you will need to add as well (x2).

Minor re-wiring will need to be done, the simplest way to set up with two t-stats would be to have the t-stats directly activate the zone valves, and the zone valves end switches connected to the boilers TT terminals.

I did exactly what you're proposing on my system last summer- it was pretty easy once you understand the concept.

 

[Sponsor]

 

[psuce]

Take a look at this article- it's very helpful and specifically addresses splitting a zone (about half way down the page):
https://heatinghelp.com/systems-help-center/loop-system-hot-water-heating-q-and-a/

Using your existing common return should be fine since it's sized for two returns already. You're splitting one zone into two- so you need to add an additional t-stat for the new zone and each t-stat will control flow to it's zone via a powered zone valve- which you will need to add as well (x2).

Minor re-wiring will need to be done, the simplest way to set up with two t-stats would be to have the t-stats directly activate the zone valves, and the zone valves end switches connected to the boilers TT terminals.

I did exactly what you're proposing on my system last summer- it was pretty easy once you understand the concept.

Thanks for the info. I took a look at zone valves first but read that some people had issues such as sticking, etc. Also, if you had an issue with the circulator, you would have no flow whereas if you split the zones with a second circulator you would have at least one zone still working. I will read through the attached article and work it into my evaluation of options.

Thanks again,

 

[NY_Rob]

You'll still need a circulator when using zone valves, but you use only one pump vs. two pumps without zone valves. You could most likely keep/use the same pump you currently use and just add the two zone valves.
You can keep a spare circulator pump on hand if you're worried about a pump failure in a single pump system.

Modern zone valves are as or even more reliable than circulator pumps. If one fails, you can operate it manually to provide flow to that zone.
http://www.supplyhouse.com/Taco-Z075C2-1-3-4-Zone-Sentry-Zone-Valve-Sweat

 

[Dana]

Based on the radiation analysis on your other thread, dumping 129,000 BTU/hr of boiler output into a zone with only 164' EDR of radiation means that the boiler would be firing at less than a 25% duty cycle when serving that zone, and about a 30% duty cycle when serving the zone with 226'. Even with both zones calling for heat it would only be about a 50% duty cycle, so the odds of zone calls overlapping are very limited. If you break it up into zones it would be highly advisable to:

A: Install the smallest nozzle that doesn't result in stack temps dangerously into the flue condensation zone. (This is very critical if you have a tile lined flue instead of a stainless steel flue liner.)

B: Install a heat-purging economizer control (eg. Intellicon HW+ or similar), programming the low limit temp to 140F (to prevent corrosive condensation inside the boiler), letting the economizer manage the high-limit.

With both of those changes the net efficiency might even improve over what it is now. If you can drop back to 0.8 gph the boiler's output will be about 94,000 BTU/hr, which will add minimum burn time, improving the duty cycle, with more overlaps from zone calls. The economizer will also pre-purge heat from the boiler on new calls for heat, delaying firing until the boiler's temp hit's the 140F low-limit, and it "learns" the system behavior based on prior burns, and estimates when the end of a call for heat is approaching, cutting the burner early, which allows the radiation to purge heat from the boiler & distribution plumbing before it falls into standby mode. That reduces total burner on-time, and reduces the standby & distribution losses to the cool, uninsulated basement.

More napkin-math:

The crude fuel-use calc based on guesstimated heating degree-days came in at a bit under 50KBTU/hr @ -5F, and you have enough radiation to emit 66,000 BTU/hr at average water temp of 180F. This means that even at -5F you don't really need the average water temp to be 180F. If the estmated 49K load is real, over 390' EDR of radiation that's 49,000 /390' = 126 BTU per square foot EDR, which can be met with an AWT of about 160F.

If the load at -5F is ~50K, at 20F outdoors the load (probably still cooler than your mid-winter average) the load is more like 32000 BTU/hr which is (/390' EDR=) 82BTU /hr per square foot, which can be met with an AWT of about 135F, which is lower than the condensing-safe operating temp of most oil boilers. An economizer would manage that, keeping the average standby temperature well under 150F, whereas without the economizer it's probably parking the boiler at 170F or higher much of the time. The difference in standby & distribution loss to a 50-60F basement will drop by a double-digit percentage, as will the total fuel used. It means the basement will be a few degrees cooler too, but for most people that's not a big deal.

Of course the better approach would be to also insulate & air seal the basement, which will also be a double-digit percentage improvement in the fuel use numbers with or without the economizer or down-firing the boiler.