Propane and electric pump heat questions

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Hi,
I live in the Boston area and am currently considering purchasing a house that has a combination of electric pump heat and propane heat. Most of the houses I've lived in and seen in the area use either gas or oil heat, so I wanted to get some opinions from the group regarding these other types of home heating systems.
To provide a little more detail, this house was originally built in the 80s with an electric heat pump. The owners installed a Rinnai based propane system about 5 years ago to reduce their heating costs. The Rinnai system is set up with propane tanks outside the house and 5 standing heating units around the house. Two of these units are downstairs, two are in bedrooms upstairs, and one is in the basement. Each of the heating units has its own thermostat. The house is large, about 3500 square feet. There is no gas line to this house
My principle questions are around:
1. Can anyone comment on the electric heat pump? Boston gets fairly cold and I've heard that these systems don't work well in very cold weather.
2. Can anyone comment on Rinnai direct-vent heating systems? I've never seen them around and wonder if there's a good reason for that. Are they efficient? Are they safe? Is it safe to have big propane tanks next to the house? What do I need to know here?
3. Presumably, I could install an oil based furnace if I wanted. Any sense for how much something like that costs? Can oil based systems do forced hot air, using the duct system that the electric pump already has in place?
I've also asked for historic heating/electricity bills. It looks like propane bills are $2000/year and electricity is about $4000/year. This seems high to me, but obviously it's dependent on what the owner's heat needs have been.
Appreciate any thoughts or comments... My initial thought is to walk away from this, largely because I don't understand the systems and don't like uncertainty. But I thought I'd get opinions from the group to see if there are different thoughts.
Thanks, PB
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I have the opposite; a propane furnace with electric HVAC in a 2 story addition. I like the balance, My fuel use is necessarily less in Texas, & heat pumps work well here at least until it dips below 30, then emergency heat kicks in at a lot more $ per hr. I think this is what the previous owner had in mind, just something to keep the heating coils from kicking on. I could see how this could be managed to not eat you out of house and home; set the unused rooms back to say 55 degrees & only bump them up when using them, lock out the emergency heat on the heat pump, all that could be done with smart thermostats. My electric heat is in the form of PTACs (motel units) & those work well if equipped with remote thermostats, the on board ones are always confused due to being right inside the unit. I had never encountered a dual fuel house before I moved here, but saw the wisdom of it the first time we ran out of propane (rookie mistake), and the first time we had a power outage (I still got my shower the addition has its own electric water heater).
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I assume your heat pump doubles as an air conditioning system also.....correct?
The heat pump is only effecient down to about 35 degrees. Also, the heat from a heat pump just isn't like flame heat. You still feel cool. Lack of humidity?
In my area, propane is more expensive than natural gas. I don't know about oil. Propane tanks are safe if not ran into by a big truck. :-)
Hank
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Appreciate the comments. Yes, that's correct - it doubles as an A/C system.
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On Wed, 11 Feb 2009 12:31:07 -0800 (PST), "Hustlin' Hank"

Sorry Hank. That sentence above from you was a totally stupid bullshit statement from one that has no idea what a heat pump can do. Bubba

Funny, mine works quite well and keeps my home warm by itself down to about 15 degrees outside. Humidity is added by a humidifier in almost any type of fuel burning furnace.

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To call my reply "stupid bullshit" isn't winning you any friends.
I had a heat pump in my last house 4 years ago. I stand by my statement that it is only efficient down to "about" 35 degrees. Below that, it is cheaper to use other heating methods. I didn't say it wouldn't heat below 35, it just isn't economical. Check the facts.
"Feeling warm" is a matter of opinion. I like to sit around in a t- shirt, so, it wasn't warm to me. I may have felt warm if I'd wear a sweat shirt. Why do people like fireplaces? I'll tell you. Because it makes "them" feel warm.
Hank <~~~wonders if there is "smart bullshit"
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On Thu, 12 Feb 2009 00:40:37 -0800 (PST), "Hustlin' Hank"

have to do with winning friends? Simple test. There are all kinds of papers that came with your heat pump when it was installed (if not, you can find them online.) One of those has the performance data for your heat pump. Check them out. Heat pumps can be very efficient even down to 0 degrees depending on your model. Look at the COP's at the lower temps. IF you dont know what that is then you dont need to be commenting. Bubba
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Let's see what some others have to say about the efficiency of heat pumps as the outside temps drop:
http://www.hannabery.com/faq4.shtml
Hannabery HVAC, Pennsylvania Now with 4 locations Serving Eastern Pennsylvania Homeowners and Businesses for over 30 years!
"In other words, if you set your thermostat for 71 degrees in the winter and your house only seems to get up to 69 degrees. This problem generates many service calls. And sometimes this is caused by a genuine problem but unfortunately, in extremely, cold weather even a properly working heat pump may have trouble maintaining desired temperature. Why is this? When it gets below a certain temperature, in our area around 35 degrees a heat pump loses efficiency and cannot keep up with the heat loss of the structure. "
Which is exactly what Hank stated. BTW, Bubba, Mr. HVAC Pro, where's your website?
Or how about this, from an electric company:
www.horryelectric.com/article.aspx?categID=11&articleID=892
"2. Auxiliary heat light ON (located on thermostat). Supplimentary heaters are providing heat (usually when outside temperature is lower than the balance point, generally 35 or less)."
Oh wait, it gets better. Here they address how with a heat pump, the air coming out of the registers will feel cooler than other heating systems. Which is something else Hank stated, which compelled you to call him names:
"The coils of your heat pump operate at lower heat levels than fossil fuel systems. Air at the supply grills almost always has a temperature ranging from 85 to 106F in the winter. Air at the registers may feel cool compared to that from other heating systems which operate at much higher temperatures for a shorter length of time."
Or how about this from the Dept of Energy:
http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12620
"When outdoor temperatures fall below 40F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. This is why air-source heat pumps aren't always very efficient for heating in areas with cold winters. Some units now have gas-fired backup furnaces instead of electric resistance coils, allowing them to operate more efficiently"
"Although air-source heat pumps can be used in nearly all parts of the United States, they do not generally perform well over extended periods of sub-freezing temperatures. In regions with sub-freezing winter temperatures, it may not be cost effective to meet all your heating needs with a standard air-source heat pump."
Now, who should know more about energy and efficiency? The DOE or Bubba?
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efficiency and effectiveness are NOT the same thing...
My heat pump is not very EFFECTIVE below 32 becasue it does not keep my house comforatbale but it is still pretty EFFICIENT. Below 32, the BTU that it puts out drops but so does the electric power that it pulls.
Below 32, I switch off the heat pump and use oil.
Mark
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On Feb 12, 1:16pm, snipped-for-privacy@yahoo.com wrote:

I would have to disagree that the lower the temperature the less electricity a heat pump will use. The efficiency of a heat pump DOES decline almopst linearly with decreasing temperature. In other words, for every KWH of electricity you put in it, you get more heat out at 45F than you do at 25F. If it were not so, then you could just put in larger capacity heat pumps and cost effectively heat homes where it was regularly 0 degrees, no?
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On Feb 12, 1:08pm, snipped-for-privacy@optonline.net wrote:

I don't know about cost effective, but I oversize my PTAC units & get heat hopefully at lower temperatures. I upgraded both of my units mainly because the newer ones were higher seer ratings. I also bought bigger units, somewhat oversize for the area, Both the upstairs and downstairs units seem to keep up nicely both hot and cool they dehumidify on AC so I guess I didn't go too far. I have no alternate in that part of the house, the gas furnace is ducted there, and I guess that was the original plan, but the ducts are just too long to be effective, so I blocked them off. There is a natural convection from the original one story to the 2 story, but it isn't enough for comfort
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You apparently "did not go too far" as you said but, for the sake of the uninitiated, let me point out that going too far, when up-sizing a heat pump, isn't hard to do. I have encountered some installations that actually were running so cold when cooling that they had condensate dripping from the vent grills. In northern climates like the Boston, Massachusetts area you are very close to the edge on the original installation were the size is pushed upward to meet heating requirements. Such heat pumps are more expensive to operate as cooling systems because they do not dehumidify as well; note I did not say at all: and so they have to be set lower to feel as cool as a unit that dehumidifies more efficiently.
-- Tom Horne
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On Feb 12, 2:08pm, snipped-for-privacy@optonline.net wrote:

the issue I have is that below 32 the outdoor coils will freeze up and the thing has to go through a defrost cycle, at that point i say forget it and switch to oil..
yes due to the defrost cycle the system is less effeicent. I think the COP at 32 is still probably 2 and above 32 it gets better...
So at 32 it is still cheaper to run then oil and at 45 or so it is much cheaper to run then oil.
I guess if you count the defrost cycle, then yes it gets a lot less efficient below 32.
Mark
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snipped-for-privacy@optonline.net wrote: ...

http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic620
That in particular is a terribly poorly worded paragraph; one would hope DOE would do better. :(
The electric resistance heaters are nearly 100% efficient; certainly higher efficiency than the gas furnace. What they're really talking about is cost effectiveness, not efficiency.
--
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Yeah, Trader probably believes this line too. "Hi Trader. I'm from the government and I'm here to help" bahaha. Trader believes everything he reads. Don't mind him too much. Bubba
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On Thu, 12 Feb 2009 08:00:07 -0800 (PST), snipped-for-privacy@optonline.net wrote:

understand energy and what it costs and what it does. A heat pump is a very efficient machine. It uses electricity but at a much better efficiency than if you were to use just straight electric strip heaters. Sometimes at almost a 4 to 1 ratio. My heat pump warms my house very well at 35 degrees. Piece of cake actually. Certainly the air coming out of the registers is cooler than a gas, or oil furnace. But guess what? It does heat the house to what temp I want it at when its 35 degrees outside and even lower. It also uses less and less electricity, the colder it gets outside but in turn produces less btu's of heat. Then, some magic happens. At a certain point, (it happens to be called the balance point of the home), the heat pump can no longer keep up with the heating needs of the house and the backup heat takes over. Is this all to hard for you trader? I know this is all way over your head trader but please try to follow along. Maybe one day you will actually learn something and I might even let you be like me. 35 degrees?! Wow Trader. You are one dumb sonz-a-biatch. Do I need to point you to one of the performance specs of a heat pump so you can understand what heat a heat pump can produce? Bubba
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No s*** Sherlock. You figure that out all by yourself? The piece you're missing here is that amount of heat that you get for the amount of electricity consumed declines as the temp differential between the inside temp and the outside temp increases. In other words, heat pumps become LESS EFFICIENT the lower the outside temp. Which is exactly the point Hank was making when you called his post stupid BS. It depends on the relative cost of the electric and the alternative fuels, but in many cases below 35, it costs less to use other fuels, like natural gas. Which is why air based heat pumps are not generally used in cold northern climates. Or if they are used, they have a duel fuel system, like nat gas. Maybe you haven't noticed. If you paid attention, the discussion was about Boston. In fact, that is exactly what the OP has. A heat pump system with additional heat from propane.
And once again, I give you links to HVAC companies and the DOE that back up both points of Hank's post, and you just ignore it.

The obvious point Hank was making is that below somewhere around 35, the efficiency of the heat pump has dropped so that you'd spend less money using another fuel, like nat gas.

It's using MORE electricity per BTU of heat that's being generated in the house. That's all that anyone cares about. My gas furnace would use zero fuel too, if it wasn't putting out any heat.

I can understand how it seems like magic to someone like you, who eschews science, engineering and education.

Just glad I never have to let a hack like you anywhere near my house.
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On Thu, 12 Feb 2009 18:02:23 -0800 (PST), snipped-for-privacy@optonline.net wrote:

facts. With all the horse crap you have pointed out once again quoting DOE and hanna-barbarra land and an electrical company, etc. I will give you a real life situation. You think that at 35 degrees a heat pump seems relatively useless. Last night, as luck would have it, It got down to below 35 degrees here in the land of make belive in Cincinnati. My Honeywell Vision Pro IAQ stat showed 35 but looking at the frozen water on my pool cover tells me it was closer to 30. I turned the gas off to my furnace last night and just let my 14 SEER heat pump do its job. I have a 1950's home with brick and block construction (no insulation in the walls) and R-38 blown into the attic. The uninsulated basement is about 75% below grade. NOW, tell me OH Wonderous one with an obviously useless EE degree. How is it that my useless heat pump as you call them maintained 67 degrees last night in my home while the temp outside was around 30?? Also tell me how my system was able to regularly cycle on and off all night , all the while when it went into defrost it was pumping in that additional cold air since I had my gas heat shut off?

chart for you and show you later.

in a labratory bubble which NO ONE on earth lives in like you.

Dont worry. You would never be so lucky. Something tells me you are quite the tight-ass and probably hacks all your own crap together. Would you like me to send you another box of duct tape, chewing gum and caulk? Bubba
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?

Funny how according to you everyone from the Dept of Energy, to Aprilaire, to HVAC companies that have been in business for 30 years are all full of crap. BTW, where are the links that support any of your claims?

Never said any such thing. Only that the efficiency of a heat pump declines as the temperature outside decreases. And at some point, below around 35 degrees or so, other fuels like gas or oil can produce the same amount of heat for less money than it costs to run the heat pump.

Gee, sounds like the Vision Pro thermostat is broken. You should call a competent HVAC guy and get that fixed pronto.

Show us once where I ever said a heat pump was useless at 30 deg. I only said that the efficiency of the heat pump declines with temp, and below somewhere around 35 deg other fuels, like nat gas, become more cost effective.

Never said it wouldn;t warm your house at 35.

So, says you. Then tell us why we don't just use bigger heat pumps that can supply enough heat for a house to be 70 when it's 0 outside? All of MN should have them. And why all the fuss about geothermal? Hmmm? If you can just as efficiently extract heat from 10 deg temps as from 50 deg temps, then why go to all that trouble of using 50 deg groundwater?

Everyone else here agrees that heat pumps use more electricity per BTU of heat generated as the outside temp drops. Hank, Mark, DOE, the HVAC company. I could give you 50 more links. Again, you're in your own little universe where the laws of physics no longer apply. I'd like to see a link from anywhere that says the efficiency of a heat pump does not decline as the outside temp drops.
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On Fri, 13 Feb 2009 11:35:51 -0800 (PST), snipped-for-privacy@optonline.net wrote:

produce cheaper heat below 35 degrees than gas and ESPECIALLY oil! I never said a heat pump doesnt lose efficiency as the outdoor temp decreases. Im telling you that it is still more effective cost wise than gas or oil below 35.

and maybe you should just Bite Me.

confusing circles when someone calls bull on your theories.

OK, bright one. Here comes lesson number 45908 for you. Yes, you could actually get a bigger heat pump or 2 or 3 of them to heat your home at 0 degrees or whatever temp you want to plug in there. Now, how cost effective would it be to purchase and install 3 heat pump systems? Now, another downfall of having say, 10 tons (120,000 btu's) of heat pump just to get enough heat to warm a 1000 sq ft. home is that when you flip that heat pump over to cooling in the summer you are going to have a home that will cool down in the summer to 50 degrees in 5 mins but wont get rid of one ounce of humidity. Now how comfortable will that house be to live in? I know that we are talking about humidity now and I know how hard of a time you have in understanding the principles of that so lets just stick to the heat pump so you dont get too overwelmed for now.

That is not true because again you are wrong. Again, why does the amperage of a heat pump compressor drop as the outside temp drops?

Yes a heat pump loses efficiency or loses the ability to produce as many btus as the outside temp drops. BUT, the compressor isnt working as hard as the temp drops thus as you would see by watching the amps. Yes, at a certain outdoor temp a heat pump has a point where it doesnt make sense to run anymore but all homes are different due to the insulating value of the home and the geographical location of the home.
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