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Why is My House Cold with Heat On Video

Tim Carter in this video explains why houses feel cold even when the furnace is operating properly.

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13 Responses to Why is My House Cold with Heat On Video

  1. Hi Tim,
    I enjoy your column very much and I always learn something new. I have learned that my HTW boiler is over sized and it is short cycling going out on pressure before the room reaches temperature. Had a survey by Mass save and installed blown in insulation,caulking that made the house warmer and quieter but it still takes 3.5 hours to warm rooms on normal cold day for Boston. Boiler seems to be over sized so I got quotes to replace but no one has done a heat load calculation. They all estimate btu's based on amount of base board in the house. How can I find a contractor in the Boston area to do a heat load calculation and install proper size boiler. We live on social security and can't afford these "trust me I have been doing this for years plumbing and heating guys.
    your help is appreciated,

    • You can do the calculations yourself since you're probably retired and have all sorts of time. Go look up: Manual J Heat Loss Calculations on Bing.com or Google.com. Believe me, it's not that hard. It just takes time and you need to take lots of measurements.

    • That doesn't sound like "short cycling" in the usual sense of the phrase -- i.e., it's not cycling off because the thermostat set point has been reached. Rather it sounds like it's turning off because of too much pressure.

      I don't know boilers well at all, but in forced air furnaces we would refer to this as "cycling on the limit" -- the furnace shutting off because it got too hot and trips off on the high limit switch.

      While over-sizing could be the cause there are other things that should be looked at. With a forced air furnace we'd look for inadequate air flow due to a plugged filter or undersized returns. I'm guessing there may be analogous issues with a boiler and hot water system -- anything impeding flow could cause this high pressure situation.

  2. Hi Tim,
    Did you know that over 10% of the US population is deaf/hearing impaired? We love your website and would greatly appreciate either captions on your videos or transcripts written below
    Thank you!
    DK on behalf of the Deaf community nationwide

  3. Hence the beauty of a variable rate (or to a lesser degree a multi-stage) furnace. Size it it be a bit more than you normally need and it will have capacity for those really cold days, but not "short cycle" on more normal or warmer days. Nice!!!

  4. Good advice and mostly correct. The "average low temperature" you say that is used to size heating and cooling systems is, more correctly, the "design temperature" for your area. It is derived from historic records of temperatures at each weather station. The winter design temperature is the temperature that is exceeded 99% of the time in the three winter months, December, January, and February.

    That's the way I learned it (and taught it) but I just checked Allison Bailes' excellent website (Energy Vanguard Blog) and found it defined this way:

    "Winter: 99% design temperature. This is the outdoor temperature that your location stays above for 99% of all the hours in the year, based on a 30-year average. Turning it around, the outdoor air where you live is going to be colder than this temperature for only 1% of the hours in a year. That happens to be about 88 hours per year. In Atlanta, the 99% winter design temperature is 23° F."

    I doubt whether the two definitions result in any significant difference. It’s particularly insignificant given that furnaces, boilers, and heat pumps only come in a fixed number of sizes and HVAC contractors also like to add a generous “safety factor.”

    The key “take away” here, as Tim suggests, is to do whatever you can to insure that you get “right sized” equipment installed. The results of oversizing a furnace is not as bad as it used to be, back before high efficiency condensing furnaces, where a natural draft appliance would never run long enough to dry out the flue system, resulting in premature failure of both equipment and chimneys. The comfort issues caused by an oversized furnace short cycling remain very real however.

    As Tim notes, oversized air conditioners are the worst. They result in serious comfort problems due to the fact that thermostat is satisfied long before the air condition has run enough to remove much humidity.

    Good video, Tim, on a really important topic!

  5. Tim, you remind me of Dennis the Mennis. A tv show I used to watch as a boy. I'm currently 64 years old and I enjoy your videos very much.

  6. Design temp for Concord, NH is -15. Your local building department should be able to give you an accurate local design temperature. Couple this with an appropriate heat loss calculation for an adequately designed heating system.

  7. It appears the home building industry still builds homes and then adapts a system to heat and cool it. Thirty years ago I could see that was the wrong approach when I set about to build a home, so I designed and built a super insulated, solar assisted home using regular building materials and methods of emerging technology. The result is a "normal" appearing home of 3,500 square feet of extraordinary comfortable living space in Kansas. The home is cooled with a high efficiency 24,000 BTU AC and high efficiency condensing gas furnace that I haven't had to turn on for the last 28 years. On non-solar assisted days I use a Century Wood Burning Fireplace/Furnace installed during construction in the core of the living space. That is the one appliance that is grossly oversized, because if used to it's max will easily heat the living space to over 80 degrees on the windiest, sub-zero days of Kansas weather. My wife and I love this home!

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