Need info for possible central air/heat pump conversion

Where I live is currently cooled by separate room air conditioners in summer and heated by oil heat in winter. The oil furnace also makes our hot water so we don't have a separate hot water heater. The price of oil is causing my mom to consider eventually switching to "something else". Also, the boiler is the original one from when the house was built (1952) so age may take its toll eventually and force us to upgrade. Right now our annual oil consumption for heating and hot water is in the 1500 gallon area. At present prices this is about $4500 but will only get much higher in the foreseeable future.

Of the alternatives, gas heat isn't particularly attractive since the price will undoubtably climb along with oil. The one thing we're both seriously considering is a central air conditioning/heat pump unit. Obviously this will entail installing ductwork since our present system is hot water heat. While the price of electricity will undoubtably rise also, the increase won't be as steep as oil price increases. As it stands now, I can't imagine that we would use even close to $4500 in electricity for heating should we go this route so operating costs should be lower. Best of all, since this conversion would make our house entirely based on electricity, we'll be setup for solar power should we ever install a system.

Now I have some questions:

1) How much more is a central air unit with heat pump capabilities as opposed to one which only cools? Since the cost of the installing the unit and ductwork will be the same regardless, then if the cost difference isn't huge we may as well have one system to do it all.

2) Will heating via heat pump be significantly more efficient than resistive heating in this part of the country? Winter highs average around 40°F and lows around 28°F but we do have cold spells where it won't get above 15°F for a week or more. Below zero temps are a rarity here.

3) In summers will the system use less electricity than we currently use for air conditioning while still having the capability to cool the whole house if need be? Would a two stage unit make the most sense? Usually we have three units on most of the time (kitchen, master bedroom, my bedroom) in the areas we usually occupy. The house is a one story ranch (24' x 42') with a finished basement. As a rough guess I'd figure we need about 40000 to 50000 BTUs to cool the entire house effectively on the hottest days but get by with 15000 or less just for the rooms we're in most of the time. We don't plan on running ductwork to the basement since we already have two AC units which can handle the cooling needs down there. Truth is the basement rarely gets above 80°F even on the hottest days so AC is more a comfort there than a necessity.

4) About how much would such a system be installed? Is installing a separate thermostat in each room feasible?

5) As for hot water, would a gas or electric hot water heater make more sense? Are any available that last longer than the usual 8 years (I'd really like something that's lifetime, especially if it's electric where nothing else can really go wrong)? Would using the waste heat from the central air unit to preheat the water be possible (i.e. is this a feature of some central air units)?

6) Will we need to upgrade our electric service? We currently have 240 VAC, 100 amp service but the breaker box only has room for one new breaker.

Please note that we're not doing this soon, meaning this year. We may do it in a year or two or three, or sooner if our old boiler finally gives up the ghost.

Thanks in advance for any help.

jtr1962 said:

Where I live is currently cooled by separate room air conditioners in summer and heated by oil heat in winter. The oil furnace also makes our hot water so we don't have a separate hot water heater. The price of oil is causing my mom to consider eventually switching to "something else". Also, the boiler is the original one from when the house was built (1952) so age may take its toll eventually and force us to upgrade. Right now our annual oil consumption for heating and hot water is in the 1500 gallon area. At present prices this is about $4500 but will only get much higher in the foreseeable future.

Of the alternatives, gas heat isn't particularly attractive since the price will undoubtably climb along with oil. The one thing we're both seriously considering is a central air conditioning/heat pump unit. Obviously this will entail installing ductwork since our present system is hot water heat. While the price of electricity will undoubtably rise also, the increase won't be as steep as oil price increases. As it stands now, I can't imagine that we would use even close to $4500 in electricity for heating should we go this route so operating costs should be lower. Best of all, since this conversion would make our house entirely based on electricity, we'll be setup for solar power should we ever install a system.

Now I have some questions:

1) How much more is a central air unit with heat pump capabilities as opposed to one which only cools? Since the cost of the installing the unit and ductwork will be the same regardless, then if the cost difference isn't huge we may as well have one system to do it all.

2) Will heating via heat pump be significantly more efficient than resistive heating in this part of the country? Winter highs average around 40°F and lows around 28°F but we do have cold spells where it won't get above 15°F for a week or more. Below zero temps are a rarity here.

3) In summers will the system use less electricity than we currently use for air conditioning while still having the capability to cool the whole house if need be? Would a two stage unit make the most sense? Usually we have three units on most of the time (kitchen, master bedroom, my bedroom) in the areas we usually occupy. The house is a one story ranch (24' x 42') with a finished basement. As a rough guess I'd figure we need about 40000 to 50000 BTUs to cool the entire house effectively on the hottest days but get by with 15000 or less just for the rooms we're in most of the time. We don't plan on running ductwork to the basement since we already have two AC units which can handle the cooling needs down there. Truth is the basement rarely gets above 80°F even on the hottest days so AC is more a comfort there than a necessity.

4) About how much would such a system be installed? Is installing a separate thermostat in each room feasible?

5) As for hot water, would a gas or electric hot water heater make more sense? Are any available that last longer than the usual 8 years (I'd really like something that's lifetime, especially if it's electric where nothing else can really go wrong)? Would using the waste heat from the central air unit to preheat the water be possible (i.e. is this a feature of some central air units)?

6) Will we need to upgrade our electric service? We currently have 240 VAC, 100 amp service but the breaker box only has room for one new breaker.

Please note that we're not doing this soon, meaning this year. We may do it in a year or two or three, or sooner if our old boiler finally gives up the ghost.

Thanks in advance for any help.

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I can help with some questions.

I'm afraid I'm not going to be able to help on install costs. As an engineer in the phamaceutical industry I don't really do residential stuff.

Before you get serious about this you will want to have someone do a heating/cooling load calculation on your house. If your house doesn't have good insulation a heat pump might not be a good choice over gas (because you will have to seriously oversize it to keep the house warm). Based on the outside temps you've listed a HP will work just fine.

A heat pump will always be more energy efficent than electric resistive heating. Like 3x more efficent.

Check with your power company. They might offer a low interest loan to pay for it (if necessary). You could also get a discount on your electricity by installing a high efficency unit. It doesn't hurt to ask.

You will need to upgrade your electrical service.

The cost of a HP will be about 20% more than an AC only unit.

It will cost the same to cool with a HP vs a normal AC unit.

The waste heat from the AC won't do you any real good. Its not hot enough to heat water.

Multiple thermostats are certainly possible. Its best to wire the 'extra' units to start the fan and have only one start the compressor.

Personally for hot water I would look at a solar/electric setup. Here in NC we get a nice tax credit to offset the purchase/install cost. Something to check into for sure. The solar tanks will last longer than 8 years.

If you need any more info I'll be glad to help.

if you have the capacity to handle wood. consider converting to wood heating.

epecially if you have a source of free wood.

I've converted to 100% wood heating last winter. when everyone was getting hammered by natural gas bills. I was heating for very low cost (free) with wood.

OK... not completely free. for I had $1,800 cost for a custom fireplace insert. but wood around here is pretty much free. you just go to our green dump, load up all you want. you do have to pay for fuel cost to haul wood and proccess.

since I love chainsaws... it's not a problem. but if you have to pay for wood. it would add up. it take aprox. 3-4 cords per season to run around here.

Heating based on heat pumps works down to about 30 - 40 F (cannot remember the actual number). Below that cut off, the heat pump is no longer effective and the furnace will use resistive heating.

The cost to run this way very much depends on what you are paying for electricity. If it is around $ 0.05 / KWH, it might be a good idea. If your pricing is like mine, where you start at $ 0.10 / KWH for a limited amount, but quickly tier up to $ 0.20 - $ 0.30 / KWH, then this can be very painful. It is painful enough that I can ALMOST justify buying a small diesel powered generator to run the meter back to the $ 0.10 / KWH part of the tier.

With a heat pump / central AC, you are essentially paying for the differential cost in inside / outside temperature, so some areas have the outside coils either partially buried in the ground, or tied into a well to benefit from the more moderate temperatures found there.

According to the manuals I have seen on A/C at least, there is a benefit to having a slightly oversized indoor coil relative to the actual capacity required. The efficiency gain can be substanital.

From a refrigerant perspective, while modern refrigerants are more ozone friendly, they are generally not as efficient - regardless of the hype. In an attempt to make up for this, they run at relatively high pressures. Thisis a good example of the very real balance of $s vs the environment. Nonetheless, it is very worth while to look carefully at the SEER numbers. A good central system is generally more efficient, quieter, and more uniform than window units.

In my own house, the builder insulated the attic to R30, but put the air ducts (which are flexible types insulated to R4) above the insulation, exposing them to the heat / cold. Over the past 2 years I have added another layer of R25 over this R30, replaced the ducts (for several reasons) to R6, and sandwiched the ducts between the R30 and R25 over layer. It made a huge difference.

Water here is quite expensive, but if you have access to inexpensive water, you can dramatically reduce the heat load on your home by evaporating water off of the roof. The key is to keep the heat from getting in in the first place. I did this to my house on a trial basis a few years ago, but my water useage was not optimized, and the bill was higher than the electricity. It did prove my point though, and we were reasonably comfortable with the AC off (not sweltering at least).

There are some natural gas powered heat pump systems that are quite interesting. They use a small engine to run the compressor and add heat to the unit. I have not seen any used commercially. There are also some gas furnaces which have a built in water heater so the unit does both. I have had to replace my gas water heater 3 X in the past 20 years, so I am not sure that this is a good strategy. Last but not least, gas is not getting cheaper. The cost to tie into a natural gas line seems like an expensive proposition.

Your current setup which I think you said is based on hot water radiator heating is actually quite optimal for efficient use of thermal solar power. This is also MUCH cheaper to install and operate. If you have room for a reasonably large water / rock thermal storage unit, you can rather cheaply and easily gather solar heat from a panel you can build yourself and mount yourself on the roof. This also can be rather easily made to work even if electricity goes out, since the pumps are low capacity. If you want to avoid a complete boiler purchase, and like the idea of electric based hot water, it might be possible to put an in -line water heater in series with your solar setup.

I don't know about your area, but locally, our houses have 100 amp breakers for the house, and a separate 60 amp service for the central AC. I would think that this would be the minimum needed for a heat pump unit, and maybe more is needed.

If you have an existing electric rate plan that makes using it attractive, then you can already gain much of those advantages now by supplementing your current heating with 1,000 watt room heaters.

You might check out a ground source heat pump. Instead of an outside unit that blows air through a radiator coil, this unit uses water. You need 2 wells, one for draw, the other for drain. Since well water is about 60 degrees F year-round, heat pumps can run *very* efficiently. Heating and air conditioning costs typically run about 40% (or less) of alternative methods. If you like, you can draw your water from the same draw well. The obstacle is installation cost. Wells can run about $7 a foot, drilled and lined, so the depth of the water table is a big consideration.

Stay with gas/oil heat and get a modern high efficiency dual speed a/c unit.

Heat pumps won't heat well or at all in your winter temps.

Wood creates smoke, and we know your propensity against that.

If I *was* looking at wood heat, I'd look at the type where the firebox is outside the house and the heat is transferred by buried water pipes. This has an advantage of heating bath water also.

A friend has one of these and they are able to burn wood/trash/etc in it. It's also got no risk of burning your house down due to a chimney fire.

Air-to-air heat pump will be marginal in winter in your/our climate. On cold winter days/nights, the unit will not run in normal heat-pump mode but will use the 'emergency' resistive heat elements. Expensive! An you should see how fast the electric meter will be spinning then! IIRC, the heat pump will need the resistive elements below about 40F. Another possibility is to have a 'split' system with a regular furnace that kicks on during cold times (fancy thermostatic controller that also checks outside temps and then fires up the HP or furnace depending on the outside temp and control set-points).

A more expensive option is to use a geo-thermal heat pump set-up. May not be possible if you can't get pipes down into the ground. But geo-thermal HP systems use the more constant temp of the ground (sometimes pretty deep ground) as the source/sink of heat.

Cost for a plain air-air heat pump could be as little as $100-$200 more compared to a 'standard' AC unit. Installation costs may vary as well.

A heat pump is usually rated as 2x or more better than plain electric resistive heat, depending on climate remember. But as it gets colder there is less heat in the air and more demand for heat from the household, so heat pumps have a definite point where they just can't supply enough heat on a cold day/night. And remember that the heat pump will usually have 'emergency' electric resistive heater elements. Once those kick on, the meter will spin FAST.

The amount of electricity used to cool the house using a heat pump system versus cooling a few selected rooms using window/wall units depends on the insulation, heat load, and efficiency of the all the units. IOW, there is no way to tell from here.

How much? No idea. But I'd ball park it as $20K+ with duct work, heat pump, and minor electrical work.

Speaking of electrical work, just looking at the existing breaker panel and checking the capacity of the main breaker is sometimes OK but often not OK to determine the capacity of the wiring and circuits. And just counting open slots in the panel really won't work either. An open slot just means it's a little easier to add a possible simple branch circuit to the existing panel, not that a circuit couldn't be added to an already 'full' panel (remove existing single pole breakers and put tandem breakers in each slot and you now have almost twice as many possible branch circuits). But doing so could easily overload the main breakers on a small rated sytem if the existing circuits are being used to capacity. Only way to tell is to use a meter and check the amps being used 'typically'.

If you are thinking of going to an electric water heater AND a heat pump, then without a doubt I think you'll need a new main panel.

Speaking of electric water heaters, what makes you think one of those will last forever? The tank will (eventually) leak, the sacrificial anode will need to be replaced, heater elements will need to be replaced, etc.

To run central AC or a heat pump, you'll -probably- have to put in a main breaker panel with more capacity (more amps capacity and more slots, not just more slots). You may need to have new feeders run into the new panel as well (the wires coming from the pole/transformer may have to be replaced to handle the larger capacity panel). Hmmm, new feeders plus new panel plus wiring the HP plus new breakers (old ones might be able to be reused or maybe not depending on vintage and panel compatability) and I'd guess an electrician will charge around $1k to $5k parts and labor.

Separate thermostats in multiple rooms? Possible. Multiple zone duct control? Possible. But the parts and labor will be more expensive.

Using AC waste heat for hot water pre-heat sounds nice, but I don't know of a residential system that does that.

Wait a minute. I just looked the the square feet of the house. It's 1008 sq ft.

That's not worth the trouble and expense. I'd just buy new high-efficiency window units for a/c.

As far as heat goes.... is natural gas cheaper than oil?

And, ANY money spent in insulation upgrades is your single best investment. Caulk, weatherstrip, attic insulation.... you get the idea.

Looking at this from a top-down perspective: something's GOT to be wrong if you're out $4500 for heating oil on a 1k sq ft house.

I can heat and cool a 5000 sq ft house for that with money left over.

my state of the art wood burning insert puts out almost no smoke and creates amost no creosole.

very clean effecient burn.. equiped with high CFM blower that you can hook to your ducts.

external wood burners are very expensive to install. VS a free standing wood stove or fireplace insert.

it would be nothing to heat 1,000 sf with a wood burner.
but it is lots of work feeding the wood fire.

if you can get your wood for low costs, heating your house on energy off the grid feels pretty good. on top of getting a small gas bill. I pay pretty the much the min amount each month.

turbodog said:

Wood creates smoke, and we know your propensity against that.

If I *was* looking at wood heat, I'd look at the type where the firebox is outside the house and the heat is transferred by buried water pipes. This has an advantage of heating bath water also.

A friend has one of these and they are able to burn wood/trash/etc in it. It's also got no risk of burning your house down due to a chimney fire.

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That may be, but he has no ducts right now.

And the outside heaters DO also heat hot water for bathing. That negates the energy required for that. And after time, that money is appreciable.

But I will stand on my head and gargle peanut butter if he installs any of these high tech devices.

cy said:

my state of the art wood burning insert puts out almost no smoke and creates amost no creosole.

very clean effecient burn.. equiped with high CFM blower that you can hook to your ducts.

external wood burners are very expensive to install. VS a free standing wood stove or fireplace insert.

it would be nothing to heat 1,000 sf with a wood burner.
but it is lots of work feeding the wood fire.

if you can get your wood for low costs, heating your house on energy off the grid feels pretty good. on top of getting a small gas bill. I pay pretty the much the min amount each month.

Click to expand...

going the wood route is definately not for everyone. in fact most folks are not willing and/or able to handle the amount of wood necessary to feed fire.

I only mentioned it because it's possibly the most cost effective way to heat you home currently available. but that cost comes at a price. which is harvesting/handling the wood.

I've got the best of both worlds. Wood heat backed up natural gas. then I'm running a water tower A/C unit with three phase power. incoming water will always be underground temp, reguardless of air temp. (in-ground heatpump)

my water tower works exactly like those huge commercial water tower units you see for very large building. only in minuture scale. it reached 107 degrees a few days ago with successive 100 degree days of weeks now. my massive A/C system has been handling the heat with room to spare. it's loafing most of the time..

the catch to all this is maintenace. it's a fairly complication system to maintain. originally my sytem had a 50's chryler airtemp semi-hermetic compressor. when it finally failed after 45 years of service.

I reversed engineered a modern copeland semi-hermetic compressor in it's place. had to remove and install compressors with a engine cherry picker. got really good with my silver soldering skills... also had to change refrigerants from 10lbs of R12 to R409A.

point of all this rambling is if one is willing/able to support the extra maintance. there are ways to heat and cool super economically.

If you are satisified with the quality of your water based heat now and your cooling methods work ok then all that really needs to be addressed is that antique boiler. Change to a high efficiancy oil fired boiler maybe update the piping in the house and maybe add some ductwork and a small fan to circulate some air.Minimal cost and change.imvho It will also still heat your domestic water.

C

That's what people say but it works much colder in my case. If I keep the set temperature on the cool side, say about 65 degrees which I do because it will be warmer in my upstairs bedroom, my heat pump works down into the single numbers before switching to all resistive. Of course as it gets colder it will run constantly or nearly so.

HarryN said:

Heating based on heat pumps works down to about 30 - 40 F (cannot remember the actual number). Below that cut off, the heat pump is no longer effective and the furnace will use resistive heating.

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I had a new Trane heat pump installed about 10 months ago and it cut my heating and cooling costs by about 50%. Here in Clearwater it seldom gets below 30 degrees F, but at that temperature the heat pump works fairly hard, so I don't know how it would do in the teens or 20's. We have been working on energry efficiency for the past 7 years. New windows, a tile roof with good insulation in the attic, energy efficient appliances, use of fluorescent light bulbs.

Last month almost every day was in the low to mid 90's. At 6:00 am when I go to work it has cooled all the way down into the upper 70's to low 80's. We cool our 1700+ square foot home to 77 degrees, use ceiling fans, and we are ALL electric. The bill we received last week was for 884 KWH total, the charge was $110 for the month. I was very excited about what we have accomplished for efficiency and cost. We don't scrimp or suffer. We cook, cool, take warm baths, wash cloths, use computers, watch TV, turn on lights in the rooms we occupy.

So, when you make your investments, look at the total package, always try to plan ahead. Look at a little additional here and there when you buy as an investment that will pay you back every month. We couldn't do it all at once but we keep energy efficiency in mind with each home item and appliance purchase we make.

Its a common misconception that heat pumps have a magic temperature that once crossed causes them to stop working. This is very false. There is a point called the balance point where the HP's rate of heat extraction falls below the thermal loss of the building (this is a function of outside temperature). At this point supplemental heat will be necessary because the temperature will continue to decrease inside the structure. Here at my house I have yet to reach this point. My HP continues to cycle and keep the house warm even with the temperature in the teens outside (I did build the house specifically with this in mind though). How do I know? My heat strips are not connected and haven't been for 2 years!

In summary, A HP does not have a magic cut off and will ALWAYS be more efficient than resistive heating as long as it can extract enough heat to keep you warm. The point where it can no longer extract enough heat is greatly influenced by the thermal efficiency of the structure. I go a bit more into this stuff here - https://www.candlepowerforums.com/posts/790936#post790936

Will a HP be cheapest in operating cost (in comparison with gas/oil/wood)?? We do not have enough information to decide this yet. That is why I suggested in my other post that a thermal load calculation be done on the house as a first step in determining the practical solution in THIS situation.

We are all offering opinions but until there is some actual data to use our opinions have limited value.

I just did some some calculations on my energy usuage for my house which I think is not effecient. My total energy usage is a little over 114 million Btu's. JTR's smaller house uses 1500 gallons of oil which equate to about 208 million Btu's and he has not listed Kwh of electricity used. I wonder how big the boiler is. I think his best bet would be to plumb in a electric water heater and not use the boiler during the warmer months. that might save him 500 gallons of oil in one year which would pay for the installation and the operation for a long time.

So much for living in "hot southern states", I use far less energy in a 3000 square foot home with 4 people versus a 1000 square foot home with 2 maybe 3 people.



edited to correct math mistake from 70 million to 114 million

If you live in a northern area where the temperatures frequently drop and stay into the teens and twentys I would guess you would need a much higher capacity heat pump. We do a lot of cooling, so to cool a house from 90° to 75° is only a 15° temperature differential. But if you heat the same house from 20° to 70°, that is a 50° difference between inside and outside temperatures so the heating load is over three times as great as the cooling load.

The heat pump we have has a dual stage compressor. Basically the unit will run at 1 1/2 ton capacity when we need minimal cooling or heating and it will run at 3 ton capacity when more is required. This allows for both more efficient operation and better summer dehumidification so we can comfortably keep the house a few degrees warmer. Here in Clearwater they installed a 5kW heat strip in my unit, don't seem to need more than that. It is my understanding that the resistive heat will also come on when the unit is de-icing so you don't get that blast of cool air during the AC cycle when heating.

Terry