# Heating question

OK, we have a pretty big living space (about 2500 sq ft. I’d say). But we only really use two rooms very much, not including the kitchen and bathrooms. One is the bedroom, where I keep my PC. It’s probably about 12x15, but it has an attached bathroom area that adds another 20 sq ft or so. The other is a large den, which is well over twice that size. Anyway, I’m trying to keep heating costs down. Would it be cheaper to keep the central heat down (to let’s say 62/63) and use space heaters for those two rooms? They wouldn’t have to run all the time on full blast (except in the den on days like today, where it’s 20s or below for the high). Or would it be more efficient to keep the central heat up a bit higher (68-70, say) and use the space heaters much less?

We also have a fireplace in the den, which I often use in the evenings to heat it up. We have a good, cheap source for firewood (\$50 for a pickup truck loaded with wood).

I’m thinking the space heaters will be better than using the central heat as much, especially on colder days, when the emergency heat kicks in a lot more.

Oh, in case it isn’t obvious, the heat is electric pump.

Hey! I woke up this morning and wondered just how efficient heat pumps would be. I have some new Fujitsu ductless AC/Heat pump units. I understand the efficiency depends on the temperature delta. Assuming you want 70 Fahrenheit indoors, then find a chart that shows how many BTUs of heat per watt of electricity are created when temperatures are 50 F, 40 F, 30 F, etc.

I’m looking at this calculator, but I need to dig out the specs on my very old gas boiler.

Forgive my foreigner noob question, but when you say your heat is electric pump, does that mean you have forced air?

Assuming yes, have you tried closing all the vents in the unused rooms and seeing if that makes a difference to your heat bill?

I know that’s something my dad does. It makes quite a difference in the temperature of two different rooms so I’m assuming that it makes it more efficient since some of the pumped air isn’t being ‘wasted’ going into rooms you don’t use.

Of course, those rooms need a door, so if he has a lot of living space he doesn’t use somewhere, it might not help that much.

I also imagine that a space heater would be much more efficient for heating one room than if you used the heat pump for the whole house, but I dunno… those heaters are 600-900W or more.

Central heating using electricity instead of natural gas.

I do that, yes. It’s a good idea, but we still have a lot of space that can’t be closed off.

Unless your central heating is an actual heat pump (e.g. works something like a fridge but with the inside of your house as the outside of the fridge), then I don’t see how the space heaters could possible be less efficienct. Most of the time when you are talking about the efficiency of some electrical device, it’s about the useful work done versus how much energy is lost to heat. With a heater, heat IS the useful work, so…

So anyway, unless your electric central heat has some kind of heat exchange process going on, the local space heaters are going to be more efficient than trying to heat the whole place.

My family has a small gas heater in our basement, and then we just use space heaters otherwise. Didn’t see much of an increase (obviously some) in our electric bill, and its cost offset what Gas would’ve been to heat the house.

The efficiency of a heater is best defined as how well it heats your home versus how much it costs to run. I’m no engineer, but I’m pretty sure there are ways to optimize heat pumps and a heating systems, meaning that some methods are more “efficient” than others.

EDIT: And some houses have valves in the basement on different ducts to stop air flow to certain rooms, that might be more effective than just shutting the heat vents independently.

Well a space heater and an electric furnace are going to cost the same per kilowatt-hour. If they both generate heat by basically passing current through an element, then I don’t see how they generate a different amount of heat per unit energy, since all the lost energy goes to heat.

Now maybe there’s some advantage to be had in how you shuffle the heat around but I’d think that a space heater, being actually in the room you want to heat, would have an advantage there.

Now all this goes out the window if his central heating does not operate on the principle of just dumping the electrical power into heat. But to do anything else it has to have contact with an external thermal mass, like pipes underground or some significant exchange with the outside air.

Maybe I’m out to lunch on this stuff, but that’s the way I see it.

Electric central furnaces are more efficient than space heaters, though.

I’d think turning off the vents when you’re not in there and opening them when you are would be the most efficient, but I’m no expert. I’d recommend calling up a few heating and cooling places to see if a guy can come out and give you advice.

I’m with the vents idea, if however your thermostat is not in the space where you spend time it probably won’t have much of an effect.

The other problem is your not having space that can be closed off. that’s a tough one to solve because eventually the air is going to move away from the place you need it, especially if it’s a setup like you spend time downstairs and all the hot air is going upstairs.

If it’s a scenario like that you may be better off with a space heater. Depending on how you spend your time maybe electric blankets would be effective. If you spend your time reading writing and playing games on the computer an electric blanket could help a lot. If however you chase kids around all day or something like that they may not be an effective solution.

Me and Mike were kind of off on a tangent, not really relevant to Robert’s problem (optimization of the efficiency of the central heating system/whether it is possible wasn’t in the question). I’d say the fireplace + space heaters would be the way to go, keeping the central heating down to just a tolerable level for when you move from room to room.

Keep the bedroom door closed and maybe look into getting some sort of decorative glass doors or something for the den if you don’t already have any, it will really help a lot if you want to confine heat to certain rooms or keep it out of certain rooms. That said, if you are able to close off both the rooms you want to heat, closing the vents could work (if you can).

My real advice however, is to do what Jason said, get a professional opinion. We are just stabbing in the dark without actually seeing the house/heating system/door options/etc.

Nah, it seems right. But he did say heat pump, which in my world is a heat exchange unit using outside air like you describe above. Depending on make and build they’re like 3-5 times as effective as simple electrical heater.

But of course if it’s warming up rooms you don’t need, that efficiency is wasted.

I know I’m coming off as a stove VM, but if you have a old fashioned fireplace that’s really a waste. It will heat the den, but will actually draw out heated air from the rest of your house… which of course isn’t a great problem if your problem isn’t wasted energy/money but just how to heat the den.

But having a modern stove or fireplace insert installed instead of the current fireplace will more than double how much heat you’ll actually get from your cheap firewood. It’s quiet amazing how large an area even a small convection stove can heat compared to old fashioned direct heat models.

That’s a good idea, Hanzii. I had a heat stove when I was young (it was our only heat for that house) and it was awesome. Since I already have a fireplace, and I do’nt really want to lose any space in that room to a full on stove, I’ll look into the insert.