Did we really need to insulate the ceiling?

katie7bOctober 1, 2007

We live in a 100+ year old brick townhouse with an unfinished basement, partially above grade. The walls are painted masonry. The ceiling used to be drywalled, but our contractor tore out the drywall when we had the house gutted 7 years ago for renovation to run new electrical and plumbing. The basment is dry with no mold problems, though we do run a humidifier in the summer. In winter, the basement is quite comfortable, I assume because of the hot water pipes running just below the ceiling joists (we have hot water radiators).

My husband recently insulated the ceiling. Now it's hot as Hades down there. Was this a mistake? Please advise!

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Is it hot in the summer or winter? If it is hot in the summer, and you are using air conditioning in the space above, then you want the insulation to keep the heat out of the conditioned space.

If it is hot in the winter, perhaps it would be better to insulate the pipes, than remove the ceiling insulation.

    Bookmark   October 1, 2007 at 9:49PM
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Thanks, Brewbeer, that helps. It makes sense now that the basement seems hotter this summer (than in the uninsulated past) because the insulation is keeping that hot air down instead of rising up into the air conditioned floors above.

Whew! I really didn't like to think we made a mistake and needed to remove the insulation.


    Bookmark   October 3, 2007 at 1:30AM
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I find it totally implausible to believe that the heat in the basement is being radiated from the hot water pipes.

Consider the fact. Typically even a large house will have under 300' of hot water piping with perhaps 50% of that in the basement. Now for the sake of argument let us say that all the pipe is 3/4". A 3/4" pipe contains one gallon of water for every 43.4' linear feet so we then have 150' of pipe, which contains 1 gallon for every 43.4' so the total hot water standing in the line at any given time is 150/43.4= 3.45gallons but to be on the safe side, let us round that up to 4gallons.

The water weighs approximately 8lbs/gal and one BTU will raise one pound of water one degree of farhenheit so the available energy is now 8BTU/gal per degree of differential temperature between the water in the pipe and the room air.

Because the floor of a basement is set well below the frost line, in winter the natural temperature of the basement slab will be approximately equal to the natural geothermal temperature of the earths surface below grade, which is 55degF. Its a basic rule of physics that Heat is a form of energy and cold is the absence of heat energy, therefore the direction of energy flow will always be from a heated space to an unheated space. This means that if the basement is not insulated there will be a small portion of the heat from the heated space migrating through the floor into the basement. In addition, there are other sources of heat energy in the basement such as the water heater vessels standby loss, radiation from both the water heater and the furnace flue pipes, clothes dryers etc so a basement that has a ceiling that is uninsulated will typically remain in the 60 to 65degF range.

Now let us examine the water pipes again.

If the water in the pipe is 125degF and if the room air temp is 60degF the differential is 65DegF. Previously we computed that we have 4 gallons of water standing in the pipe and it contains 8BTU per deg of temperature differential. This means that with a differential of 65DegF the available heat from the water in the pipes is 65x4=260btu x 4 gallons equals a total of 1,040BTU

That is 1/35 the energy of the water heater or laundry dryer burner or 1/150 of an average residential gas furnace. In fact, it is even less than the BTU energy emitted from a 60 watt light bulb.

That is also about 1/20 the heat loss of a 12x12 single pane glass window with an outdoor temperature of 30DegF. I fail to see how this slight amount of heat energy could contribute significantly to heating the basement.

    Bookmark   October 5, 2007 at 10:02AM
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we had hot water pipes that ran in and out of our crawl space to baseboards up stairs. Those pipes warmed the crawl space area.

    Bookmark   October 5, 2007 at 11:02AM
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The heat could be coming from the dehumidifier.

    Bookmark   October 5, 2007 at 5:37PM
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