New heating /AC

Discussion in 'HVAC Heating & Cooling' started by Geo422, Apr 11, 2019.

  1. Geo422

    Geo422 Member

    Joined:
    Feb 12, 2012
    Location:
    Cin oh
    Advice 1100 sq foot house with 2 bedrooms on second level.
    Needs a complete new heating and Central air.
    What brands and etc would you experts recommend.
    I took an old cast iron converted furnace out and have a clean slate to deal with. Thanks Geo422
     
  2. WorthFlorida

    WorthFlorida Broad-Wing Hawk

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Please give some additional information

    1) Type of fuel used. Electric, fuel oil, natural gas or propane?
    2) Type of heating system? Hot water circulation or forced air?
    3) Can a new furnace be installed on an exterior wall?
    4) Did this old iron furnace use a masonry chimney?
    5) Is there a separate water heater? If yes did it share the chimney with the old furnace? Fuel type?
    6) Assume a basement location?
    7) Any idea on home insulation values, attic, walls, etc. and window type?
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. Geo422

    Geo422 Member

    Joined:
    Feb 12, 2012
    Location:
    Cin oh
    House built in 1938. Natural gas and water heater. New furnace will vent outside by a pipe through wall. The old iron furnace was converted from coal to gas.
    New system will be natural Gas with central air conditioned. Basement install outside walls very open area
    House is getting new insulation , double windows , new siding with house wrap .
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Was it a furnace or a boiler?

    Your biggest issue with a gas-furnace (if not a boiler) would be finding something right-sized for your actual loads. Getting a good grasp on your heating and cooling load numbers will be essential for maxing out both comfort and efficiency. A 5x oversized furnace or air conditioner will heat & cool the place, but it's the opposite of comfort.

    Do you have enough of a heating history on it to run a fuel-use based load calculation on wintertime-only gas bills? Since that is the "before upgrades" picture would establish a firm upper bound on the furnace sizing.

    Start with a room by room, zone by zone Manual-J type load calculation. If using an freebie online version such as loadcalc to calculate the loads be aggressive on R-value, infiltration & duct leakage assumptions or it will oversize by quite a bit.

    Most tightened-up 1100' 1.5 story houses would have a design heat load at +12F (Cincinnati's 99% outside design temp) would be less that 17,000 BTU/hr, and could be less than 14,000 BTU/hr if the basement is insulated to the current IRC code minimum. The only gas hot air furnace I know of that fires that low is Detton's modulating Chinook series, which is a bit special. The smallest 2-stage condensing Goodman GMEC96 0303ANA is still over 20,000 BTU/hr at low fire (and I think it's been discontinued) but would be about as good as it gets in more standard 'merican style equipment. A hydro-air handler running off a condensing water heater can be appropriately sized for smaller houses, but that requires a bit more design smarts by the installers.

    You may be better off with a 1.5- 2 ton heat pump solution, even though that's almost certainly oversized for your cooling loads. A modulating 1.5 ton Fujitsu -18RLFCD or -18RGLXD wouldn't be too bad though, since either could modulate down to less than half your likely load, yet still deliver ~18,000 BTU/hr @ +5F (over 20K for the 18RLFCD). The -18RGLXD is an easier retrofit onto existing ducts due to it's higher static pressure capacity, but the ducts are probably sufficiently oversized to do OK with the cheaper, higher capacity and more efficient (but less beefy blower) 18RLFCD.

    It's likely that you'll want to zone the upstairs and down stairs separately. The heating and cooling loads of a couple of upstairs bedrooms is pretty tiny, probably less than 8000 BTU/hr in the "after upgrades" picture, which is within range of Fujitsu's 7RLFC mini-duct cassette, which would have to be used with a multi-zone compressor. A 2 ton AOU24RFXFZH can run up to 3 zones, but setting it up with a 12RLFC or 18RLFC for the main floor and a 7RLFC for the upstairs would work reasonably efficiently. At max speed that 2 ton compressor will deliver 25,500 BTU/hr @ +5F, (which is overkill for your house), but it has a decent modulation range, and can throttle down to 6100 BTU/hr @ +47F.

    At 2 ton Carrier Infinity Greenspeed doesn't have the same modulation range or low-temp capacity of a Fujitsu (and would probably be more expensive), but it could surely handle your loads.

    BTW: Since that house was almost certainly sheathed with ship-lap or t & g planking it isn't very air tight. Even though it's quite a bit more expensive than Tyvek/Typar etc, a fully adhered vapor permeable membrane housewrap like Blueskin VP100 would be a cheap efficiency upgrade in the end, vastly reducing air infiltration issues. (Think of it as 4' wide strips of housewrap tape.) Fully adhered membrane housewraps are really the only way to do plank sheathed houses right without resorting to foam insulation cavity fill and lots of detailing with caulk & can-foam.
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    A pretty good primer on why you don't want to oversize the equipment any more than absolutely necessary is covered in Nate Adams' videos describing some of his book chapters.

    Nate Adams has been in the house retrofit biz for a long time, and is doing pretty well for himself in the Cleveland area addressing the real comfort issues of houses beyond mere insulation and air tightening, treating the house and mechanicals as one system. He is therefore big on right-sizing the equipment, which for lower load houses means right sized heat pumps rather than gas hot air + oversized split AC.

    Nate also looks at trends and has become a strong believer in electrifying everything. At the rate costs of solar & wind are falling and driving wholesale electricity pricing down (putting big central plants into economic hardship), heating with heat pumps will be cheaper than condensing gas in most markets within the lifecycle of the equipment.
     
    Last edited: Apr 12, 2019 at 2:32 PM
Similar Threads: heating
Forum Title Date
HVAC Heating & Cooling Bathroom remodel - electric radiant floor heating? Feb 4, 2019
HVAC Heating & Cooling What happens when the heating system is not maintained. Feb 2, 2019
HVAC Heating & Cooling Radiant Heating Not keeping up Jan 22, 2019
HVAC Heating & Cooling Adding radiant heat to existing hydronic baseboard heating Apr 16, 2018
HVAC Heating & Cooling Inefficient electric duct central heating Jan 18, 2018

Share This Page