Adding a zone for my basement to a single zone house

Discussion in 'HVAC Heating & Cooling' started by Mandinca, Sep 19, 2020.

  1. Mandinca

    Mandinca Member

    Joined:
    Jun 16, 2020
    Location:
    Connecticut
    I have a 1250 sq ft split level home and the main level is heated with one zone of baseboard radiators. The oil furnace provides both the heat and hot water.

    Since there is no zone valve and presumably no aquastat on the existing set up how can I add a zone and thermostat to heat my 400 sq ft basement ?

    Do I need to add an aquastat and create two zones with their own valves or is there another way ?

    I want to be able to independently heat the basement rather than heat the basement at the same time as the rest of the house.

    Thanks.
     
  2. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Thermostat, pump, heat emitter and boiler control like a Taco SR503. Which would give you priority dhw and control of both zones . You have a aquastat now that controls boiler water temp. Someone needs to run a load to see how much heat you need.
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. Mandinca

    Mandinca Member

    Joined:
    Jun 16, 2020
    Location:
    Connecticut
    So would the plumbing be something along the lines of....

    Boiler, a single line exits the boiler and splits before feeding two zones each with their own pump. When a thermostat calls for heat the SR503 powers the related pump and hot water pumps around that zone accordingly until the thermostat stops calling for heat. Is that correct ?
    Can both "zone returns" T back into one line for re-entry into the boiler at the end of the loop ?

    How do I go about running the load you mentioned ?
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    This may be a dialect issue, but generally a heating appliance heating pumped hot water systems is called a "boiler", and not "furnace". In the HVAC world the latter term generally refers to distributing the heat via ducted hot air delivery. Conflating the two terms can be a source of confusion.

    Since the heat loss characteristics of basements are quite different from fully above grade floors it's wise to set it up as an independent zone.

    The heat load of a 400' basement is pretty small even if the foundation walls are not insulated to the current code-minimum R15 continuous insulation, but may be small enough to self-heat on the standby losses of the ridiculously oversized burner relative to the design heat load of a 1250' house. Odds the heat requirements for the whole house (basement included) are less than 30,000 BTU/hr, and could even be less than 20,000 BTU/hr if the house is reasonably tight and reasonably insulated, but to serve up hot water at a reasonable rate usually requires a >100,000 BTU/hr burner for the boiler, 3-5x the design heat load, and the idling temp of the boiler usually has to be maintained at 150F or higher to deliver reasonable mid-winter hot water performance from an embedded tankless coil, which has significantly higher standby loss. (To get a handle on your actual heat load, run a fuel use based load calculation on some of last winter's fill ups, which uses the boiler as a measuring instrument.) If the foundation walls aren't already insulated it might be worth taking on that project first, which will make the place more comfortable whether it's actively heated or not.

    There are several ways to skin this cat. Teeing a separate branch between the boiler and the existing pump to the basement loop with a separate pump, and controlling both pumps with a zone controller works. To limit zone flow interactions a pump with built in check valve, or separate check valves on each loop is usually necessary. Without check valves there will be a slow back flow on the basement zone radiation whenever the main zone is running, and at the low load of a basement that back flow could even overheat the space. And yes whether zone valves or separate pump, the returns simply tee together prior to where it enters the boiler.

    Another approach would be to run a small hydro-air coil using potable water, leaving the heating loop alone. As long as a potable-compatible pump is used (typically stainless or bronze body) and all plumbing on that loop is potable-grade it's legal in most states (and low risk) to run heating zones with potable hot water, usually with some limitation on the total length of plumbing. The plumbing won't be an issue in a 400' basement if the boiler room is in the basement (or anywhere inside a 1250' house).

    Using online Manual-J-ish type load tools such as LoadCalc or CoolCalc is a reasonable start. Though both of those tools will oversize some, they usually don't oversize by 2x or more, a fault of many simpler (stupider?) load calculation tools. Deriving accurate loads for uninsulated basements is more difficult than for insulate above grade floors, due to the wide variation in the thermal characteristics of soils. In your case oversizing the radiation isn't going to be a disaster- even though the zone radiation won't emit anywhere near the full burner output, the load is so small that it won't short-cycle the burner due to the amount of thermal mass in a typical oil boiler. (For lower mass boilers short cycling could be an issue.) With only calls for heat from just the basement zone it's likely that the thermostat will often be satisfied just by the stored heat in the boiler, and the call for heat ends before engaging the burner, and the burns per hour (or day) will be minimum, even if the burns are short.

    It's likely that even on the first floor zone there isn't enough radiation to emit the full burner output but a big enough load that there might be a short-cycling issue. As the heating season gets going, measure the burn times- if they are typically running <5 minutes per burn it's worth addressing.
     
  6. Mandinca

    Mandinca Member

    Joined:
    Jun 16, 2020
    Location:
    Connecticut
    Dana, lots of information there, thank you very much.

    My weekend warrior brain is in overdrive.
    Yes, I meant the boiler, I have hydronic baseboard heat.

    I had a look at the heat load calculator....might be a bit confusing for my brain, too many permutations that I am unsure of.
    So then I went to the fuel based load calculation link - it's dead. Do you have any alternatives ?

    For what it's worth, I have about 80 linear feet of the larger type of slantfin (3/4 copper with 3" fins).
    1250 sq ft, 8' ceilings throughout. One main floor with an insulated attic space. It was built in the 50's so I will "guess" that it's poorly insulated in order to get a worst case scenario to see if the current set up will support the additional basement load, which presumably is what this is all for. Windows are wood frame, single pane with very cheap storm windows, and look to be original or at least 30-40 years old.
    My boiler set up is a bit more complicated because the boiler has a large label on it with three model numbers - it's not indicated which one is mine.
    Looks like the 100/75/60 means GPH.

    Lennox
    COWB-3-100C
    COWB-3-75C
    COWB-3-60C

    The burner is a Becket AFG - no model number visible.

    The circulator on the current set up is on the return side, right before the boiler. I would have to move it back up the line a couple of feet to install a second pump and still have room to tee that second pump into the line before entering the boiler. I have room to do that.
    With that said, where the water exits the boiler presumably I am allowed to split that line so that the second zone is fed from the same main line, right ? Essentially (in electrical terms) I'm creating a simple parallel circuit that starts right where hot water exits the boiler and ends where the now "used" water re-enters the boiler. The first circulator is plumbed into one of the parallel lines and the second circulator is in the second parallel line ?

    Then the TACO SR503 is wired to each circulator, each thermostat and to the current aquastat ?

    My basement is half foundation and half unfinished insulated studs. My plan was to build new walls from floor to ceiling, just inside the existing exterior walls and insulate those new walls with R13. Then put 6mil plastic and sheetrock over the top.


    This all seems logical to me.....but......weekend warrior :)

    Thanks
     
    Last edited: Sep 21, 2020
  7. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Taco control- either zone calls turns on its pump and boiler. If your domestic hot water calls, turns off heating zones turns on the boiler and its pump if water heater isn't up to temp in one hour heating zones are turned back on.
     
  8. Mandinca

    Mandinca Member

    Joined:
    Jun 16, 2020
    Location:
    Connecticut
    Clever stuff, thanks for suggesting it, I never would have thought to run two pumps on separate switching like that. My rather limited experience is of adding a zone to an already two zone system operated by valves so just added another valve and figured out how to wire the thermostat in.
     
  9. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The link works for me as of a few seconds ago- perhaps their server was under maintenance when you tried it?

    Try again, this time spelled out:

    https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new


    At an AWT (average water temp) of 170F (180F out of the boiler, 160 return) 80' of typical SlantFin baseboard emits about 42,000 BTU/hr. So if the place has been staying warm even during Polar Vortex disturbance cold snaps the design heat load at the 99% outside design temp is well under 40,000 BTU/hr.

    You might try an IBR type load calculation using a spreadsheet to verify the heat load.

    Typical 1950s wall insulation was R0 (=empty cavities) to R11, rarely R13. If it's been retrofitted with blown in fiberglass, rock wool, or cellulose figure on R13. The framing fractions of most 2x4 framing of the era is about 25%, meaning that 25% of the wall area has thermally bridging studs/headers/top & bottom plates, etc behind the sheathing, at about R 4.2, which has to be taken into account when calculating the "U-factor" (- BTU/hr per degree F temperature difference per square foot of wall, not counting windows & doors). So at a 60F temperature difference (a typical 99% design temp for CT of 10F outdoors, 70F indoors) the heat loss of above grade walls is

    U-factor x 60F x area of framed wall= BTU/hr

    With typical sheathing and siding options the U-factor of an empty wall cavity at a 25% framing fraction is about 0.36BTU/hr per degree F temperature difference per square foot of wall (not counting windows & doors), an R11 runs about U0.11, a typical R13 wall runs about U0.10. For a quick & dirty pretty good rough-cut, U0.10 is usually pretty close.

    The framing fractions of roofs and ceilings are typically much less, an there are are similar tables for roofs & ceilings.

    The wild card is the basement & foundation walls. A typical poured concrete wall with no interior or exterior cladding or insulation runs about U0.1 (includes air films) , a hollow core block wall about U0.7, but it varies a lot, and that's only for above-grade portions of the walls. Whatever it is, the heat loss of uninsulated foundation wall is still significant, and can be reduced by an order of magnitude bringing it up to current code minimums (R15 continuous insulation). There are real mold & rot risks to insulating the foundation with just a non structural batt insulated wall, but it's not hard to do it in such a way to keep it dry and mold free, summer & winter. I'll spare the details unless you're going that route.

    Single pane wood sash with clear glass (not l0w-E) runs about U0.5, as do 2" solid core doors or clear-glass (not low-E) double pane replacement windows. Use the full net area of the window opening, not just the glass, and don't include the window casing (consider that wall area.)

    Air leakage also has to be estimated and accounted for, but is usually WAY overstated in the Manual-J or IBR assumptions. Unless the place leaks air like a tennis racquet through walls & ceilings (which sometimes happens with uninsulated houses) I usually assume 3-5 cfm per window & door.


    With an embedded coil for hot water yours is almost certainly the COWB-3-100C, with a 1 gallon per hour nozzle. (Burner techs usually leave a tag with the nozzle model and the raw combustion efficiency on the boiler when performing a tune-up.) The source-fuel energy in a gallon of #2 oil varies a bit, but it's around 138,000 BTU/gallon. Burned at 85% efficiency it means only (0.85 x 138,000 BTU/hr = ) 117,300 BTU/hr went into the heating system, the rest went up the flue. But that's still nearly 3x the amount of heat that your baseboard can emit (and many times the amount of baseboard needed to heat the basement would emit.)


    Read the installation sheet on the SR503 on how to wire it up- it's pretty simple. The SR503 turns on the pumps separately by powering them whenever the zone thermostat calls for heat. With most boilers with embedded coils the boiler aquastats operate independently, and are not operated or called by the thermostats directly. There is usually a zone relay or similar control managing the pump. Read the boiler manual to figure out how yours works. (I might look at it later, if I have the time.)

    It doesn't take much pump to run the basement loop- a Taco-007 is overkill, a Taco-003 or similar would be fine. A "smart" pump such as the AquaMotion AM55-FVL offers a lot of control and can run at very low flow, extremely low power, (for a price), but a Taco 007e running in "green" mode or other not-too-smart but ECM drive pump is the best bang/buck, if complete overkill for the application. It'll use only about 10-15% of the power that an 007 (not-"e") would, and is only about $35 more at internet pricing. If going with zone valves it may be worth springing for a single AM55-FVL or a Taco VT-2218, but even there the 007e is probably still going to give you most of the benefit at a lower price point.
     
Similar Threads: Adding zone
Forum Title Date
HVAC Heating & Cooling Adding Zone with Fixed Speed Furnace Jun 10, 2021
HVAC Heating & Cooling Adding a Zone to a Boiler Jan 9, 2017
HVAC Heating & Cooling Adding new radiant heat zones to existing system Feb 21, 2015
HVAC Heating & Cooling Adding Zone valves to Honeywell Aquastat L8148J Mar 6, 2014
HVAC Heating & Cooling adding zone control to system Sep 29, 2013

Share This Page