What's the most efficient / least inefficient way to heat 3 season room?
December 8, 2014 12:12 PM   Subscribe

Our house has three season room we love. Winter is not one of the three seasons. What's the most efficient / least inefficient way to heat it up for an afternoon periodically?

It gets pretty cold in there--probably hovering in the high 30s these days. We haven't tried to warm it at all since the first week of November, when we used a small oscillating space heater (sort of like this one, but that model or maker). It takes a couple of hours, and then you can turn off the heater. Once the room is warm, we can open the doors to the heated part of the house and the temperature is pretty stable, even with the heater off.

It's nice to sit out there for brunch when we have guests over--as we will for the Christmas holidays.

Given that it's never going to be efficient to heat a 38 degree room up to 68 using an electric heater, what's the least inefficient way to do it? Should we get a larger oscillating heater (like the Dyson)? Would it be better to get one of the radiator-style heaters?

Again, this is for mostly one-off use in the dead of winter, and maybe more frequent use in the very early spring and very late fall. I have no interest in using the space heater to maintain comfortable temperatures all the time--so to the extent it matters, we're talking 30 or more degrees of heating, but only periodically.
posted by Admiral Haddock to Home & Garden (11 answers total) 2 users marked this as a favorite
Are drafts an issue, and if so, can you put some kind of seasonal sealant on the windows, like the plastic wrap kind you heat up with a hairdryer? This will not be the best bet if it is a fancily windowed room where you want to enjoy the view.

I have found that the oil filled radiator heaters take an astonishingly long time to really heat up a large space in comparison to the heat blower kind, but the former is a lot easier on your electric bill.
posted by poffin boffin at 12:16 PM on December 8, 2014

This would be a considerable up-front expense, but cheap thereafter: install a small wood-burning stove.
posted by jon1270 at 12:37 PM on December 8, 2014 [4 favorites]

Have you looked into kerosene heaters? They are pretty terrific for making larger very cold spaces quite toasty in a reasonable time frame.
posted by kmennie at 12:38 PM on December 8, 2014

The biggest barrier to quickly heating a cold room is heating up the walls and ceiling. You can heat the air very quickly, but until the walls are warm you've got these huge slabs absorbing all the heat in the room. As the warm air heads toward the cold walls, the convection currents can feel like cold air is rushing in through the wall. (And then the heat moves by conduction from the inner to outer walls. Insulation and air-sealing slow this process considerably.)

The most-efficient way to heat the room would be to open that door about 12 hours prior to using it so the rest of the house can passively heat it. This will make heating the rest of the house less efficient, of course. Assuming there aren't any huge gaps around doors or windows where heated air can directly escape, your heat loss should be manageable. The room will never be as warm as the properly-insulated spaces, but you can keep it habitable.
posted by sportbucket at 12:42 PM on December 8, 2014 [2 favorites]

Response by poster: Poffin, no air leaks at all--but the room is floor to ceiling glass (modern double glazed sliding glass doors).

I should have also said that the room is a cube measuring about 10x10x10. I don't think we're going to do anything involving combustion.
posted by Admiral Haddock at 12:42 PM on December 8, 2014

Propane or other gas (or perhaps even kerosene...) would be a lot easier on the pocketbook these days than anything electric.

However, forcing the air to circulate will definitely help; this probably explains poffin boffin's observation that a simple radiator takes forever to heat the space (because you only get convection and it goes straight to the ceiling). Could you install a ceiling fan in there, and then combine with some transient gas heat device? The fan could pull dual duty on warm summer nights as well.
posted by Joey Buttafoucault at 12:45 PM on December 8, 2014 [1 favorite]

Radiant floors would be a great solution for a sunroom, especially since you have high ceilings - though perhaps not worth the time/expense if you only want to use the room occasionally.

Similarly, a pellet stove could be great (though certainly costly upfront).

Of the portable heaters you link, I would get the Dyson if cost isn't an issue. I have the DeLonghi myself and it is great and very efficient, but they warm up slowly - I would guess the electric one works faster.
posted by susanvance at 1:02 PM on December 8, 2014 [2 favorites]

I agree with the propane idea a Mr Heater works well and can put out way more BTUs that a electric plug in heater (VoltsXamps=Watts). I have heated a shop for years this way. I found a fan blowing the cold air from the floor up, or one blowing the hot air near the ceiling down will make a big difference of how well this works. The fan can can be quite small.
Be sure to leave a window open a crack or a door opening to the porch open to ensure a supply of fresh air. You can put a carbon monoxide detector in the room if you want to be safe.
posted by boilermonster at 2:05 PM on December 8, 2014

Once the room is warm, we can open the doors to the heated part of the house and the temperature is pretty stable, even with the heater off.

Opening the doors before the room is warm will speed up the warming of the room using the heat from the rest of the house, which is generated more efficiently than the electric space heater.
posted by justkevin at 2:12 PM on December 8, 2014

I just bought a Vornado electric heater to warm my 10x20 room that has no other heat source. It is FABULOUS!! It takes a while to heat up but it is quite comfy throughout the whole room when it does. The way it circulates the air is the most helpful part I imagine. I also haven't ceiling fan on to keep the air stirred up.

Don't know about cost efficiency because I haven't investigated that, but I do know a heater that circulates the air works great.
posted by MultiFaceted at 5:10 PM on December 8, 2014

All electric heat is 100% efficient and will essentially heat your space the same. Different electric heaters can feel warmer or colder to people but they heat the room on a degree temperature rise per watt basis in exactly same.

boilermonster: "I agree with the propane idea a Mr Heater works well and can put out way more BTUs that a electric plug in heater "

A non vented gas heater dumps a butt load of moisture into the air. Like almost a pound of water for every pound of propane. So while it might be cheaper in your area you have to have a plan to deal with the moisture.

But really running a plug in space heater for a couple hours is pretty cheap; certainly cheaper on such a intermittent basis than spending money on a new heater (plus its associated input energy costs and the costs associated with buying that fuel) of any sort. Your standard 1500W heater ran for two hours only costs $1.15 even in Hawaii with it's very high $0.38/KWHr electric rates. Everywhere else in the US it'll be less than half that (only 27 cents in Washington State)
posted by Mitheral at 7:34 PM on December 8, 2014

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