A heating conundrum

July 5, 2007 3:58 AM

I have a plug-in space heater. I also have radiant heat. Which is more economical for heating a basement room?

My basement media room is 350 square feet of finished, insulated space. Unheated, temps hover at 57 degrees F in the winter, 64 degrees F in the summer (and 55% humidity controlled by a dehumidifier). Temperatures that, in other words, are fine-n-dandy for storage, but not exactly the bomb when I'm watching DVDs.

The radiant heat tubing snakes through the poured concrete slab, and heats the room to 70 F in about three hours. Takes another three to cool down. The space heater moves the mercury to that point in about an hour, but I sense that the floor, which is cold and uncarpeted (I'll remedy that soon with a low-r-rating, radiant-heat-friendly carpet), sucks away the heat.

Out of 24 hours, I only need two hours of heat per day.

Yep, just two hours. Enough heat to get my two-episode fix of "Battlestar Galactica," after which I pack up and leave. Of course, any electricity-versus-heating oil comparison will be ballpark at best. But which system, on the face of the above data, would be cheaper to run? And, as a corollary question, how do dehumidifier settings affect the efficiency of my heating choice?

posted by Gordion Knott to home & garden (9 comments total)

Okay, we need the height of your room, whether it is an above ground or below ground basement, and the output in watts of your radiant heat as well as the space heater.

Off the top of my head, though, I'm going to say it is going to be a combination of the two. Space heater to bring it close to normal temps and radiant heat to maintain it there for the next hour. The cool down time of the radiant heat isn't really an issue, since you aren't paying for that.
posted by Loto at 4:29 AM on July 5, 2007

Loto, the room is 8 ft high and a below-ground basement. The heater is 1200 watts (although I could purchase a space heater with higher or lower wattage if needed).

I'm not sure of the wattage for the radiant heat.

Currently, my heating "system" consists of a hot-water baseboard portion (for the rooms above ground) and a single zone of radiant heat for the basement.

Right now, the radiant part of my heating system circulates water at 120 degrees F, substantially lower than the 150 degress F that is sent to the hot-water baseboard portion of the system.

When my boiler is running 10 to 15 hours a day in the winter, it might be economical to use more radiant than electric heat -- because the water in the system has already been heated for the hot-water baseboard usage.
posted by Gordion Knott at 4:53 AM on July 5, 2007

This doesn't really answer the question but, if you only want 2 hours of heat a day I imagine something that would heat the place as fast as possible, set on a timer to reach a minimally acceptable temperature by the beginning of the 2 hours. Similarly, to take maximum advantage of the cool down time, determine how far into those 2 hours you can turn the heat off, so that the room cools to a minimally acceptable temp by the end of the 2 hours. I imagine space heaters are best for rapid heating. Keep in mind that this is just a thought experiment, and I have no experimental evidence.
posted by DarkForest at 5:16 AM on July 5, 2007

Also, I think radiant heat isn't so much about heating the room to a particular temperature, but about heating you directly with it's yummy radiant rays. In other words, you might feel warm even though the air temp reads lower than you'd like.

I'd kill for a 64 degree room in the summer.
posted by DarkForest at 5:20 AM on July 5, 2007

One more thought - just cozy up in a nice warm blanket for those 2 hours in front of the tube. Costs nothing.
posted by DarkForest at 5:24 AM on July 5, 2007

Can I choose option (c), which would be to use an electric blanket and not heat the whole room for two hours of use? Or (d), a reflector-type space heater that would concentrate the heat on your viewing position?

I suspect that answer is that it's more efficient to use the radiant when the boiler is already running and the space heater when it's not, but I have no data to back that up.
posted by backupjesus at 5:25 AM on July 5, 2007

Well, there's more to think of:

Is your hot water heater gas or electric? How many gallons are used for your closed-loop radiant floor system?

Chances are that it takes significantly MORE energy to use use the radiant for such a short period of time, because the water/propylene glycol is cooling off, which entirely defeats the purpose and effectiveness of radiant floor heat.

Although...do you have radiant floors in the rest of the house, as in zonal-radiant? If so, then I figure it's way more efficient to turn on the basement, but I could be wrong.

Also, like the earlier guy said, one of the great things about radiant floors is that they can be turned to a MUCH lower temperature because of the way they heat and the way your body perceives that heat.

So...in summation: for 2 hours a day, assuming NO heat any other time, the plug-in would probably be best, especially if you get or have gotten a high efficiency one. (Which is a joke, because heating with resistance is NEVER efficient).

Although, you might find that leaving the basement on at 62 degrees or so keeps the rest of your house heat easier and you can ramp up that room to 65-67 and get it warmer in half an hour.

Personally, I'd murder-death-kill for a radiant floor system. Of course, you can always get handy and make a passive solar water heater, and then you can heat your basement radiant system for $0.
posted by TomMelee at 7:16 AM on July 5, 2007

Which is a joke, because heating with resistance is NEVER efficient.

Actually it is just the opposite. 100% of the energy from an electrical resistance heater, no matter how designed, goes into your house whereas with gas, about 20% goes up the chimney. The real difference is that electricity costs more than gas per BTU which generally overshadows electricity's greater efficiency.
posted by JackFlash at 9:56 AM on July 5, 2007

Meh, splitting hairs. Heating with resistance takes a significant amount of power....as in a 1500 watt heater is NOT a big heater, but will require a large draw. (large in terms of if that power was used for just about anything else....realistically a coil-heater is a big easy-bake oven with a fan behind it, only a bigger element and not in a vacuum.)

While it may be TRUE that 100% of the power goes into generating heat, in this context I mean "not efficient" in a output versus input manner.

And there are certainly gas heating options with well over 80% efficiency---an 80% model these days is bottom of the line. Even in those cases, there are interesting ways to recover that heat.
posted by TomMelee at 7:02 PM on July 5, 2007