No, I don't agree with that. Since you are on fuel oil for lower outside temps, I would run that HP down to 25 degrees at least and then evaluate for comfort and make adjustment as needed. I see nothing in your list about a heat strip.

IMO

My Carrier equipment is ~6 years old and I have Oil Heat as the backup. tigerdunes helped me arrive at 25 degrees as the crossover point here in MD.

Your equipment presumably has a higher COP than mine and I suspect Oil Cost and Electic rates are not too, too different.

I would not be surprised if something lower than 25 degrees turns out to be even better...

I have no strip heaters on my Hybrid Install.

If you have a basement Electric Hot Water heater I would sure look at a Hybrid Hot Water heater... it saves my wife and I about $40 each month in reduced electrical usage.

I'd probably go lower but it all depends on the relative cost of electricity and oil. Heatpumps are less efficient at lower temperatures and older ones may cost more to run than oil baseboards. However the Greenspeed is about the most efficient heatpump out there and should be good down to below freezing

Ask the installer why he chose 35 degrees. If he can't give you a believeable answer, as to speak to someone who can.

Give me your fuel oil cost/gallon and electric cost/kWH and I will do a down and dirty fuel cost comparison for you. I would like to hear an explanation about the strip heat.

IMO

Economic and temperature balance points...

tigerdunes- thanks very much for the guidance here. We paid $2.09 per gallon for oil during the most recent winter. We pay $0.2075/kwh . No heat strip has been included (yet) since the primary motivation of the install was to add central AC to the home.

I would want a heat strip to al least temper the air on a defrost cycle for your Greenspeed HP. Without it you will be pumping in full AC during winter defrost cycles. Not good!.

IMO

Is it possible to add the heat strip mid install? About how much would cost be with labor in your view? Thanks for all the guidance!

tigerdunes,

My Carrier HP plus Oil Heat seamlessly uses Oil heat briefly to heat during defrost.

I have no electric strips. The oil usage for this purpose in my MD locale is minuscule.

Also, adding strip heaters would seemingly require a electrical service upgrade.

for Salti

As I understand, OP has existing oil boiler for baseboard heat. He wants to add AC and a High EFF HP seems to make sense versus expensive fuel oil. I have not yet had a chance to run the numbers but don't see how a boiler can temper the air on a HP defrost call. Take a look at OP's initial post. As I recall you have a forced air DF system, HP paired with oil furnace.

IMO

And of course, you're the man tigerdunes!

I can see the issue with baseboard heat.

BTW, thanks for your help to so many of us over many years here!

of course Salti, I always follow your posts!...thx

very high electric rates...using the fuel cost info provided, I made the following assumptions...82% oil boiler eff, 3.50 COP HP efficiency...

Cost per 100,000 btu of useable heat:

Electric baseboard:$5.47

Heat pump:$1.74

Oil:$1.85

you need a heat strip, size 8-10 KW for tempering air on defrost calls. it should be installed at time of initial installation. I think one has to weigh whether HP is worth it with high electric rate plus a top of line Greenspeed system.

i will assume no natural gas availability. Yes/no?

IMO

Tiger- thanks again for the input. Unfortunately no natural gas available on our street. Any rough estimate of cost to install heat strips? While I appreciate your candor and input, this now makes me incredibly frustrated with the service provider for not knowing this information. They are a large outfit and not cheap.

You are purchasing a very high end heat pump system. I am not sure if it is worth it. However, have you asked dealer if a heat strip was included in their quote? And if not, ask how the new HP system would temper the air on a defrost call. Installation cost should be nothing. The installers will already be on site. In fact, I think dealer should provide a heat strip on their dime, not yours. However not more than $250-300.

Any chance that nat gas gas will be brought to your street? I definitely would call distributor and ask the question b4 purchasing this HP system.

IMO

If I do a simple extrapolation of the numbers, the cost of operating the heat pump and the boiler are equal when the heat pump COP is 3.3. The question is at what outside temperature will that occur?

A fuel oil price of $2.09 per gallon seems low. You must have a very large fuel oil tank and locked in the price several months ago.

You electricity price is high. Have you looked into getting a better rate from a third party supplier?

The economic balance point between the heat pump and boiler will change as a function of energy prices. Wouldn't it be great if you can enter prices and efficiencies into the thermostat and have it calculate the optimum outside temperature at the economic balance point!

I checked current pricing for your area on home heating oil and see $2.60/gal as a good average.

TD

This changes the computation on fuel comparison...Cost per 100,000 btu of useable heat using $2.60 gallon on fuel oil...

Electric baseboard:$5.47

Heat pump:$1.74

Oil:$2.30

With diesel getting over $3/gal now, fuel oil should be similar in price, perhaps higher. More so this winter. If you can get a 'lock-in' price early, that will be good.

I think you'll find you can operate the Greenspeed to lower temperatures.

The two temperatures you need to think about is the temp at which you'll want to turn on the boiler and circulator pumps for the baseboards (unless convective) since it will take a while for them to heat up. And the temperature below which the heat pump should not run. Anything might just be a guess, but I might start with 28* at the upper and 15* at the lower.

YMMV.

No road tax on "diesel" sold as fuel oil or for offroad use (boats, farm equipment, etc), that accounts for part of the price difference between fuel oil and diesel at the gas station.

At 36 degrees the 24VNA036 can generate a maximum of 30K BTU of heat. That may be below the heat loss of the house. If the boiler is cut off from operating the heat pump may run all day and not be able to maintain the temperature set point.

Just to insert another opinion here. There are a few more things to consider. I think Tiger’s estimate of existing oil boiler efficiency is overly optimistic at 82%. Depending on age, 65% might be more realistic.

There’s no info on existing ductwork, was it designed for AC as in ceiling mounted that would not be optimal for heat distribution? What type of radiators are installed, aluminum finned or cast iron? What water temperature does the boiler have to heat water to, 140˚F or 180˚F? That also makes a big impact on efficiency and energy consumption!

Average COP for a 3-ton Greenspeed in our region is calculated at 3.8. We’re in Montreal. Let’s for argument’s sake say the weather is comparable to Boston in winter.

Greenspeed should be run down to a temperature of at least a low of +5˚F. According to Carrier, balance point in Montreal of a 3-ton Greenspeed in a 3000sq Ft home is calculated at ~+5˚F base on the BIN data for Montreal, 1,866hrs of AC & 6,894hrs of heating. Boston is not worse for heating.

I think your electrical rate is sky high, however, the market for oil is very volatile. The price for electricity will likely be stable, oil, who knows.

You’re looking at 2-very different systems that might not be easily integrated. If going with Greenspeed, oil might best be left as just a backup system. Where’s your oil tank; I hope not buried in the ground!

You would need those backup electric heat strips previously mentioned, perhaps 15kW and staged. You might also have to upgrade your electrical entrance to 200amp.

IMPO

SR