GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Energy (oil) use single home in Zone 4 (03818). 2800 sqft built 2004.

bpbuilder | Posted in Energy Efficiency and Durability on

Blower door test Air Exchanges per Hour (ACH) = .347 (based on a Volume of 13,787 cubic feet). R26 walls R50 (vert measure) sloped ceiling. Windows u.35 I currently use 597 gals/yr average over 5 yrs any thoughts?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. gusfhb | | #1

    type of heating system?


    thermostat setting?


    is that heat only or heat hot water?

  2. Expert Member
    Dana Dorsett | | #2

    Seems like a LOT of oil use for tight better than code house in a zone 4 climate- there must be a lot of windows &/or you're also heating the domestic hot water with oil (?). Any foundation insulation?

    In a zone 4 type climate you'd likely be able to heat the place with mini-splits at something like 1/3 the cost, paying for itself in 3 years.

    But if 03818 is your ZIP code (Conway NH) you are in US climate zone 6a not zone 4, and that's a reasonably LOW annual oil-use figure. In that climate a pair mini-splits would take something on the order of 5-8 years to fully pay off in heating savings, though a well-placed single mini-split could pay itself off in 3-4 years. With U0.35 windows you would likely have comfort issues in doored-off rooms remote from the mini-split heads if that's the sole source of heat during colder weather, but there are work-arounds. In the past 5 years you've spent something on the order of ten grand or more on heating oil, and mini-splits would cut that in half:

    A better class cold-climate mini-split will deliver seasonal average heat output of about 10,000 BTU/kwh in Conway NH climate. at 16.4 cents kwh (the NH average according to EIA data) that's about 61,000BTU/$ of heat delivered into your house. An 85% efficiency oil-burner delivers about 117,500 BTU/gallon, and at $4/gallon that only 29,375 BTU/$, about half the heat you'd get for the same dollar using mini-splits.

  3. bpbuilder | | #3

    Foundation insulation 2" Dow blue down to the footing. Zone 4 is the plant grow zone is the heating different? Six zone radiant heat oil fired boiler 85% eff. Thermostat 67* I have added (2011) 5 EURO L20 AR (7'x4') solar hot water panels. The savings is still not clear installation performance problems. Saved 85 gls of oil the first year! Mini-splits as in ductless wall units? Thanks for the imput

  4. davidmeiland | | #4

    Just to clarify the blower door number, it sounds like you are saying the predicted ACHn is .347, not that ACH50 is .347...?

  5. bpbuilder | | #5

    From the doc of the blower test. Blower Door Test reading = 1180 cfm50 Air Exchanges per Hour (ACH) = .347 (based on a Volume of 13,787 cubic feet) Does that clarify? Thanks Bob

  6. davidmeiland | | #6

    Thanks. Just wanted to know that we're not talking about a super-tight house here.

    As Dana says, the real savings (at today's prices) are in abandoning the oil boiler and going to electric ductless heat pump(s). You could probably cut your heating cost in half.

  7. davidmeiland | | #7

    Here's a calculator you can use to do comparisons...

  8. bpbuilder | | #8

    Abandon the radient!! That's not going to happen. I'd sell the house and build another. But at 68 yrs old....I my rent ;o(

  9. davidmeiland | | #9

    I know what you mean. My last house had radiant, this one does not... well, it has a woodstove that radiates, so at least there's that.

    I've seen some interesting air-source heat pumps for hydronic. Not long ago I checked out a system that used a typical 2-ton outdoor unit with a refrigerant-to-water heat exchanger similar to this image. It heated a large storage tank to provide floor heating.

  10. Expert Member
    Dana Dorsett | | #10

    The Daikin Altherma air-to-water system does pretty well even at -10F, despite only having specified output down to -4F. But it's a heluva lot more money than a mini-split. Depending on the required peak water temps of your radiation it may or may not be a reasonable retrofit. But you're looking at fifteen grand, best case, as opposed to ~$4-5K for a 1.5 ton mini-split that can deliver 20,000BTU/hr at Conway's -5F-ish 99% outside design temp.

    At 600gallons over 7000 heating degree days that's about 10,000BTU of boiler output per HDD, or ~420 BTU per degree-hour. In a 70F room and -5F outside design temp that's 75F heating degrees, for an implied peak heat load of 75F x 420 BTU/degree-F= 31,500 BTU/hr, but at Conway's binned-hourly January mean of 20F the heat load is 50F x 420BTU/F= 21,000 BTU/hr, which would be fully covered by the ductless. That means that a single 1.5 ton mini-split could deliver over 80% of the total heat in January , and over 95% of your annual overall heat. (Even at -5F it's still good for about 67% of the load! )

    An electric boiler slaved to floor thermostats along with mini-splits to set the room temp can deliver 100% of the cushy-warm floor feel while letting the 'split handle the heating load, and come in a lower operating cost than an oil boiler if you don't push the floor temps too high- maybe 1-2F above the room ambient, and turn off the electric boiler during the shoulder seasons. At 2F above room-ambient the radiant delivers about 4 BTU per square foot of active floor. So if you have 1000' of active floor, that's 4000 BTU/hr- roughly half your heat load when it's 50F outside. At that temp the mini-split would be 4x as efficient as an electric boiler, so if it's covering half the load the electric boiler is just KILLING the average efficiency. But you'd get to choose your barefoot-comfort vs. efficiency equation that way.

    A 9-10kw electric boiler runs ~$1500 + installation, and has enough output for 100% of your heat load. Even the smallest oil boilers are more than 2x oversized for your heat load, and without heat-purge control won't it it's AFUE efficiency numbers.

    Plant hardiness zones are about peak-low temps/frost dates and rainfall, whereas the HVAC climate zones are all about heating and cooling degree-days. A map for the latter can be found here:

  11. davidmeiland | | #11

    Does he have floors or wall rads?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |