heat pump vs. Vornados

October 11, 2008 8:26 PM

Is it cheaper to run a full house heat pump during colder months, or use Vornado heaters to heat subsections of the house that we are in at the moment.

I've got a two bedroom house with an attached studio apartment, all heated by one heat pump. Our climate is Pacific Northwest....kind of rainy and cold about 6 months of the year but not drastically freezing except on rare occasions.

We have a pair of 1500 Watt Vornados that we move around the house. They do a fair job of keeping rooms fairly livable without using the heat pump. These are older Vornados....once you turn them on they stay on full blast and do not cycle the power or wattage depending on temperature.

I don't know what the studio dweller uses for heat, but it would probably be useful to find out.

So, I'm wondering, how can I figure out which is the cheaper alternative, using the Vornados or the heat pump?

posted by diode to home & garden (5 comments total)

With AC, it's always preferable to run it all the time and keep it relatively cool than let it cool down a hot room over and over, I would assume that the same holds for heat. If you run the heat pump, it will keep your house always warm so you won't have to heat up a completely cold room every time you move.
posted by Mach5 at 8:35 PM on October 11, 2008

It's a difficult question to answer since it depends on a lot of variables. To begin with, a heat pump can be 2 to 4 times more efficient than an electric resistance heater. What this means is that for every dollar of electricity you spend for the heat pump, you get 2 to 4 times as much heat as you do with the portable heaters. So generally you would be better off heating with the heat pump. But this depends on how new and efficient your heat pump is.

On the other hand, you would be heating parts of the house you may not be using. The effect of heating the whole house depends on how well insulated and weather sealed the house is. If well insulated, then heating the whole house isn't that much worse than heating just one or two rooms. But with the radiant heaters, you may be comfortable with a lower air temperature than you would require with the heat pump.

The only real way to tell would be to run a test and compare your power bills. The problem is that the outside temperature changes from month to month. But if you plot your power bill from month to month you should see a smooth curve of higher bills as you go from September to January and then decreasing bills from January to summer. If you switch from one heat source to the other for an entire month, you should be able to see if there is a jump in one direction or the other that stands out from the curve.

But just guessing off the top of my head, I think the heat pump is going to be cheaper if it is reasonably efficient and you get a smart thermostat that turns off the heat when you are sleeping or away at work. It's hard to beat 2 to 4 times better efficiency.

What isn't clear from your description is who pays for heating the studio apartment. If you run the heat pump do you end up paying for the tenant's heat? If you don't run the heat pump, does the tenant pay for his own heater?
posted by JackFlash at 11:38 PM on October 11, 2008

Do you have a ground source or air source heat pump? One complicating factor is that when the air temperature drops low enough, air source heat pumps aren't as effective, and so they often use gas or electric resistance heating to bridge the gap. In that mode, you are probably better off spot heating with the Vornados.

Otherwise, if you are going to the trouble of turning the Vornados on and off, and moving them from room to room, you might consider sticking with the central heating and just opening and closing heat vents as you move from room to room. That way you get the efficiency of the heat pump, without heating up rooms unnecessarily.

BTW, it isn't true that it is more efficient to leave AC running. The larger the temperature differential, the faster heat transfers between cold and warm areas, so your constantly cool house is going to absorb a lot more heat over the course of a day than it would if the AC was off. The same is going to hold true for heating, though in the opposite direction. Now, there are other reasons you might want to leave AC running while you are out of the house. It *might* be kinder to the compressor to have it running intermittently through the day, than to have it run flat out for a long stretch to cool the house back down again.
posted by Good Brain at 12:15 AM on October 12, 2008

In China, I've only once seen central air conditioning or heating and I've been in some pretty fancy, large, opulent houses. I've always thought it had to do partially with the cost of heating large spaces. One particularly useful addition to the mix, though, is that just about every room has a sliding glass door with rubber seal to keep the warm or cool air exactly where you are and no where else. Seems like a good way to do it, and I'm sure you could set up a timing mechanism to take the briskness out of really cold mornings.
posted by msbrauer at 5:34 AM on October 12, 2008

Well, I never did get this answered to my satisfaction. I had our local utility here the other day running a duct leakage test. I asked the energy conservation person the same question and it was like asking a lawyer for a straight answer in 20 words or less.

It was almost absurd listening to how many ways this person could avoid giving any kind of estimate or figure. I ended up thinking I wasn't asking the right question.

Since I cannot directly measure the wattage being pulled by the pump (my meter gives a digital count, not a spinning dial I can time for a current read on the watts being used) I figured it would somewhat reasonable to ask people what's the typical draw by the unit.

I figure that the pump has a fan outside, a fan inside in the furnace unit, plus the heat pump itself, so overall when the heat pump is working on a typical day where it is in use, perhaps 45 degrees out and cloudy it's got to draw more juice than one 1500 watt heater.

The response I get tends to be that it is more efficient, therefore cheaper, which is not what I am trying to establish. When I use a small space heater, I'm just trying to warm up a small area around me, not the whole house. It works fine. Could it be that the heat pump in use on a typical day (45-50 degrees in cloudy weather) is using about the same wattage as a space heater? Literally no one has hazarded even a wild guess on this, so I'm still somewhat in the dark on this subject. Really I should ask an HVAC tech.

Anyhoos, was over at a friend's house enjoying how their wood burning insert kept their house warm and dry while my heat pump blows air everywhere, is relatively noisy and is electricity burning, so next step is pricing inserts I think.
posted by diode at 10:02 PM on February 23