Keeping my hot side hot and my cool side crisp

August 15, 2008 6:19 AM

When is a heat pump worth it? [warning: a bit long]

Due to circumstances that are really too long to explain, I need to totally remove my oil heating system and replace it with an electric system. Quotes to tear out the old furnace, upgrade my ductwork and put in an electric furnace come in at about $4K. That's pretty much a given. Adding a heat pump, however, would cost about $5K to $6K. I currently have no air conditioning in my very old house with very old windows, and while I don't mind suffering a bit to save a few bucks, my fiancée is very much of the opposite opinion... but she currently lives in the southern States, and isn't really familiar with Canadian summers (it only gets stinkin' hot from about mid-July to mid-August where I live).
The pluses of getting the heat pump are essentially that I'm getting everything torn up to put the new furnace in and wired up right now, and installing something like a heat pump later would be much less convenient than getting it done now. It's also a "fire and forget" kind of solution for the next era of home ownership: get it done and it'll never have to be done again.
It's a two-story house built into a hill, so the upper floor is at street level and is entirely aboveground; the lower floor is below street level but is 90% aboveground thanks to the slope of the hill. About 80% of my time is spent on the upper floor -- the lower floor is my workshop, workout room, guest room, furnace room, storage space and a second bathroom. Total square footage is about 1800 sq.ft. divided evenly between the floors.
Since I've never had electric heat OR air conditioning, I'm in no position to compare expenditures vs. projected savings to cost out whether it's worthwhile. I'm tempted to put the $6K towards new windows, but that'd just be a drop in the bucket as far as window-replacement costs. The windows I have now are entirely unsuitable for window-mount air conditioners, and I'm not convinced those are a good idea at the best of times.
Most of the resources I've found re. heat pumps need you to figure out what you've been spending on heating/cooling for the past X years, but I don't have any such data. Previous threads like the one for Atlanta thread is interesting but not especially relevant for my situation. The Arkansas AskMe was a bit more helpful, but I'm more interested in its cooling properties than the heating ones.
I can't think of any other relevant information, but feel free to post more questions if that'll help me puzzle out whether or not this is a good move.
The environment is also a concern: while I know a standard air conditioner would be cheaper, is there one option that is much more green than the other? I'm already happy to be switching from oil to electric, as Quebec power is relatively green (mostly hydroelectric from northern dams).

posted by Shepherd to home & garden (19 answers total)

I'd be very surprised to find that a heat pump wouldn't save you at least 50% on energy costs compared to a simple heater, and I'd be very surprised to find that the extra $2000 wouldn't pay for itself well inside five years.
posted by flabdablet at 6:28 AM on August 15, 2008

I would check out financial incentives that your area (town, county, province?) might offer to offset the cost of installing the heat pump. I'm about to install one in my upstate New York house, and the state of New York is knocking 4% off the interest rate of the smallish loan I'm taking out to do it. Combining this with the savings I'll be getting from the efficiency of the pump (not to mention the SKYROCKETING price of oil and natural gas in the northeast), I'm convinced this is by far the more cost-effective option for my small house.

Also, more anecdotally, my parents have had one in their house for 20 years now. It's magnificently efficient. My parents regularly pay 1/2 of what their neighbors do. Also, it's quiet! The humidifier and ultraviolet air purifier that they had appended to their system is a boon, too.
posted by minervous at 6:38 AM on August 15, 2008

Heat pumps are identical to air conditioning during the cooling season.

They work for heat down into the 30s (F). They are actually very efficient for heating- over 100% efficient. Electric heating is also quite efficient, but it only approaches 90-something%. The reason heat pumps can get that efficiency is that they use the electricity to move heat from outdoors to indoors, rather than just "burning" the electricity for heat.

Of course, you'd have to switch to electric heat in the depths of winter. In your scenario, you may not break even for quite some time. On the other hand, it is a more green solution.

Basically, you need to decide whether you want air conditioning. If you do, what's the difference in installation costs between a heat pump and regular A/C. I'd imagine it's only $1000. So you'll probably get to break even for the costs in a few years because of the savings realized during the mild heating season.
posted by gjc at 6:38 AM on August 15, 2008

You know, I was assuming you were talking about a geothermal heat pump. From reading the prior threads you linked to, that might not be the case, and so my comment might not apply.

(If you were, I also want to add that they can also serve as supplemental or sole water heaters in the house, depending on your climate and needs.)
posted by minervous at 6:41 AM on August 15, 2008

No direct advice, but this article from the times yesterday might help...

http://www.nytimes.com/2008/08/14/business/smallbusiness/14sbiz.html
posted by scooby at 6:45 AM on August 15, 2008

Link here.
posted by scooby at 6:46 AM on August 15, 2008

Not geothermal, I'm afraid -- air-powered. The location of my house and its position relative to neighbours, the street, the slope of the hill, and the size of the yard mean that there's no practical place to sink the pipes, and no economical way to get the massive machinery required to the one place that a pipe could perhaps be sunk without thousands and of dollars in additional costs.
posted by Shepherd at 6:52 AM on August 15, 2008

A heat pump will always be more efficient than electric resistance heat. The heat pump more or less "moves" heat to where you want it (inside in the winter, outside in the summer) through compression and expansion of a refrigerant. In the worst possible situation, where the outside temperature is too cold to wring any usable heat out of the air (around <2>
If it regularly gets below 20F for extended periods of time, you may want to look into a propane backup system.
posted by electroboy at 7:04 AM on August 15, 2008

oops, got cut off. Was going to say that heat pumps typically have electric resistance heat as a backup if it gets below 20F.
posted by electroboy at 7:07 AM on August 15, 2008

My parents have a heat pump as their primary heat during the winter, have a not-large house, and it runs pretty much constantly when the temperature is below freezing. They've been advised that heat pumps really don't fare well with constant running, and to expect about a five year lifespan on them. This held true for their first replacement heat pump, although I'm not sure if they've had better luck since then.
posted by mikeh at 8:10 AM on August 15, 2008

I just moved into a house with a heat pump, and although we haven't spent a winter with it yet, I did notice that the thermostat has three modes: Cool, Heat, and "Emerg. Heat".

The third mode seems to shut off the compressor and instead just heat the air with big resistance coils located near the blower (near the coils that the air normally flows through). Judging from the electrical supply it has attached to it (240V 50A circuit), it's a fairly substantial electric heater. I don't doubt it's capable of heating the whole house.

So if you get a heat pump and it has electric backup, you won't need to worry about ever being cold. At worst, you'll need to switch to the all-electric mode, which is only ~100% efficient instead of the 200-300% that a heat pump can get under good operating conditions. (Ground source can be 300-500%, apparently.)

Our feeling is that if it gets cold enough (we're in the Mid-Atlantic region in the U.S., so it really doesn't get that cold) to start having to run the electric backup, we'll use oil-filled electric space heaters to spot heat, rather the heating the whole house, and maybe use the fireplace. (We have an EPA insert for the fireplace, which makes it fairly efficient as a source of heat. Almost all the benefit of a high-efficiency stove in less space. Might be something to consider.)

Since a heat pump will act just like an electric-'burning' system in the worst case, but be much, much more efficient in the best cases (spring and fall at least), and will get you an air conditioner (which you don't have to use, if you want to save the money) ... I think you'd be silly to go with a straight electric furnace. If you can get some subsidies to help with the cost or lower your interest payments on any loans you'd be taking out, all the better.
posted by Kadin2048 at 9:34 AM on August 15, 2008 [1 favorite]

Just keep in mind that even though electric resistance heat is 100% efficient, it's still really expensive.
posted by electroboy at 10:25 AM on August 15, 2008

They are actually very efficient for heating- over 100% efficient.

Nothing is over 100% efficient. You're confused.
posted by odinsdream at 10:26 AM on August 15, 2008

Nothing is over 100% efficient. You're confused.

Confused about terminology perhaps, but not about the actual energy use and costs in question. See Coefficient of Performance.

An electric resistance heater adds 1 Watt-hour of heat to the heated space for each Watt-hour of energy consumed, giving a CoP of 1 (100%). A heat pump, depending on the outdoor temperature, can typically move 3.5 Watt-hours worth of heat from the outdoor air to the indoor air (the heated space) for each Watt-hour of energy consumed, giving a CoP of 3.5 (350%).

Of course the heat pump machinery itself is not "over 100% efficient," but it doesn't need to be in order to deliver what most people would think of as "350% efficiency" and what will certainly show up on one's electric bill as such.
posted by Juffo-Wup at 10:42 AM on August 15, 2008

Just keep in mind that even though electric resistance heat is 100% efficient, it's still really expensive.

One of the advantages of living in Quebec is (comparatively) cheap electricity.

These responses are great -- I'm learning a lot and making a little list of questions for the HVAC guy. If you have any other advice or experience, please keep it coming!
posted by Shepherd at 10:45 AM on August 15, 2008

One of the advantages of living in Quebec is (comparatively) cheap electricity.

Have you personally verified that electric heating is cheaper than natural gas heating (or whatever else is popular in your locality)?

Power plants are not 100% efficient, due to the Carnot Cycle. So using $1 of natural gas to generate electricity, and then that electricity to generate heat, gives you less heat (and hence less heat per $ of gas) than using the natural gas to generate heat directly (which is close to 100% efficient).

In my country at least, electrical heating costs several times more per watt than gas heating.
posted by Mike1024 at 11:46 AM on August 15, 2008

That's a good point, Mike1024, but the fact of the matter is I have to remove the oil system and I can't install another one for a variety of reasons that are really tangential. I have heard from enough people that electric is cheaper than natural gas that I've opted for electric (I'm also a bit paranoid about natural gas, having narrowly escaped explosive death in Toronto years ago).

So: electric heat is a given, geothermal is impossible, solar is a luxury (plus I live halfway up the north side of a mountain, which is awesome in many ways but terrible for solar arrays). I'm definitely getting an electric furnace. The question is whether a $6K (aboveground) heat pump is a good investment or a waste of money.
posted by Shepherd at 12:18 PM on August 15, 2008

I see you're in Canada - make sure you find out if any of the grant amounts under the Eco-Energy program are available to you.
posted by davey_darling at 12:37 PM on August 15, 2008

This mentions all-climate and cold climate heat pumps. They may be worth looking into.
posted by sebastienbailard at 2:37 PM on August 15, 2008