Actual temp vs. "feel"?

[JohnnyG]

There seems to be many times in our home when the house feels cool even though the temperature on the thermostat is on - or even above - it's set point. What can be the causes of this? Environmental issues don't seem to play a part in this as the t-stat does not get hit by sunlight nor is there a register nearby. Is it possible that the relative humidity in the house is making it feel cooler? If so, are there any thermostats that take humidity into account?

[57]

Actual temperature vs Thermostat? Have you checked the temperature where YOU are with a separate thermometer? If the house is not well insulated/sealed, then there could be "breezes" in the home, especially when it's windy outside, which would make one feel cool, especially if near a door or a window.

Fan running? Do you run your fan 24/7. If the fan is running and the furnace is off, the circulating air could make it feel cooler (wind chill).

Relative Humidity: The RH could be a factor since higher RH indicates more particles in the air, which could make the air that passes you, or surrounds you feel cooler. This is not usually an issue in the heating season. Do you have a hygrometer to measure RH?

Circadian rhythms, Menopause, Activity: Circadian rhythms mean that you can feel different at different times of the day. (Especially true for females and females reaching a certain age). The amount you are active will impact whether you feel warm or cool, usually the less active, the cooler.

[JohnnyG]

I had a thermostat/hygrometer in the house but it's mysteriously vanished. Perhaps it was taken by the same ghosts who are making it feel chilly

I've sealed up many drafts in the house but I'm not done yet, so this is likely part of the problem, but there have been days when it was calm outside but still felt cooler in the house than the thermostat was reading.

[wgauci]

Check the relative humidity in your house. Lower RH will result in a cooler feeling at the same temperature. I always tell my clients that 75 degrees in Florida always feel warmer than 75 in Arizona. The higher the moisture content in the air the warmer the air will feel.

There are stats that have integrated humidy control as well.

[57]

wgauci, I agree with you when the temperature is warm - it's the humidex, however, I don't believe that the humidex would come into play in the heating season, especially in a house that is not well sealed. If the temperature is cool, then a higher humidity can cause the air to feel cooler because there are more molecules per cubic foot. This would of course depend on the dew point in the home, but my guess is the dew point would be below 12C, therefore Humidex doesn't come into play.

[txv]

Heat transfer is a function of radiant and conductive losses. (Evaporation aside)

Surface temperatures have an impact on perceived comfort. (Cold walls, windows, etc can reduce the perceived temperature)

[wgauci]

57,

It has to do with the moisture content in the air. There are a lot of references to how humidity levels equate to comfort levels in your home.

If humidity is too low
Low humidity causes static electricity, dry skin and hair, and itching and chapping. Mucous membranes in nose and throat dry out, increasing your discomfort and susceptibility to colds and respiratory illness. With low humidity levels, body moisture evaporates so quickly that you feel chilled even at higher thermostat settings. Adding a humidifier to your home will remedy these problems. There are three standard types from which to choose.

http://www.blueflame.org/datasheets/humidity.html

The lower the moisture content in the air, the more evaporative cooling your body feels.

[JohnnyG]

I think that's it then. We installed a new furnace Spring '06 and have yet to install a humidifier. The house is definitely on the dry side.

[txv]

Measure the RH before assuming that it's too low. At this time of the year it should be 30-45%.

If it's low, note that a humidifier is just a patch for excessive air leakage. When cold outdoor air with little capacity to hold moisture is heated, the relative humidity drops dramatically. Usually evaporation from showering and cooking is sufficient to raise the RH back to a reasonable level, provided the infiltration is not too high.

Draft proofing can save you hundreds of dollars worth of energy and water over several years, not the mention the $200-$300 initial outlay for the humidifier.

[Monobloc]

There seem to be varying views on humidity.

In Vancouver, having lower humidity will mean you feel warmer at 18° than when it's humid and 18°. There is no such thing as too dry. 18° and 40% feels better than 21° and 55%. No damp feel when it's dry.

In Saskatoon, it will be so dry in the winter that you'll need either better air sealing and/or a humidifier.

On the other hand, a drafty house even though it will be dry, will feel cold.


The above is in the winter......in the summer it all reverses so that low humidity means you can get away with higher thermostat set points.

78° in Arizona is typically 30-35% inside. 75° is freezing in AZ. Many don't even run air conditioning, but instead run swamp coolers. (Giant sponge that is fed water by a pump and then a fan is blown over it. Cheap to run as there is no compressor.)

78° in Florida is possible with 35%, but you really need a good system to do that. Unfortunately most people get a system that puts out about 45-55%, so they need to lower the thermostat to 75° (or lower) to feel comfortable. No swamp coolers in FL as swamp coolers don't dehumidify. They increase the humidity (which of course isn't an issue in AZ)

My recommendation? Buy some slippers!

[Uncle N]

"...higher humidity can cause the air to feel cooler because there are more molecules per cubic foot."

The total molecular density doesn't depend on humidex or dew point, but a higher dewpoint will mean more water molecules and less of the others. At room temperature and above, a higher dew point will always feel warmer; it's just a matter of degree.

[57]

Clarification:

At a dew point of 12C and above, there is a "humidex" factor. At below 12C, there is no "humidex" effect. Since this is a house and we're talking about the heating season, it's highly unlikely that the dew point in the home is above 12C, therefore if you're comparing a dew point of 5C, with a dew point of 10C, the additional (water) molecules in the air possibly could cause the air to feel cooler, especially say if the actual temperature in the room is only say 18C. This runs counter to the humidex effect we're all familiar with, but that's because the humidex effect is preventing evaporation from the skin for cooling, while that is not a factor at dew points below 12C.

[Airbalancer]

You are better off to run your furnace, it should reduce hot & cold spots
But most house duct design & installations are crap.
People will spend more on their AV system then their HVAC systems

[Tritboss]

I doubt there are any thermostats that will factor in the relative humidity in the air. However, you can connect a humidistat to the humidifier on your furnace. If you do this, you need to adjust the setting periodically depending on the outsisde temperature to keep to much moisture from condensing on your windows when it gets really cold outside.

The humidistat on my furnace came with a label recommending a setting of 35% at an outdoor temp of -7 °C, 25% @ -18 °C and 20% @ -23°C.

57- I think you're way overthinking the humidex thing. It's really just a measurement of the temperature we percieve based on the air temp and its moisture content. The more water vapour that's in the air, the less perspiration evaporates from our skin, resulting in us feeling warmer than we would in dry air at the same temperature. Any moisture in the air is going to slow the rate at which sweat evaporates from the skin, regardless of whether it's above 12°C or not.

A house with a RH of 40% @ 20 °C will have a dewpoint of about 6°C (look it up if you don't believe me). If you were to drop the RH to 10% at the same temperature, the dewpoint would be about -12°C. You would ABSOLUTELY feel the difference (and you'd likely be getting static shocks off everything you touched at the lower RH_

[Uncle N]

At a dew point of 12C and above, there is a "humidex" factor. At below 12C, there is no "humidex" effect.

Given that the effect arises from the presence of water molecules in the air, and in the atmosphere there is always water vapour, the effect is just a matter of degree, as I stated earlier. Also, since people perspire to varying degrees, they will perceive the humidex effect differently.

As a practical matter, the formula developed by Environment Canada, available at Wikipedia, shows a humidex effect of essentially zero at a dew point of 7C, rising more or less linearly to 2.3 degrees at a dew point of 12C. For example, air at 20C with a DP of 12C should feel like 22.3. This is probably why I've seen recommendations (although I can't reference one at the moment) to keep the living space humidified in the winter as an antidote to lowering the 'stat setting.