Heat pump vs dual fuel for heat

[rfuerst911sc]

So our retirement house that we purchased two years ago has a Trane dual fuel furnace . So when heat requirements are light it heats via the heat pump . When the temp sensor says I need more heat the LP furnace kicks on . The system was built and installed in 1996 .

This past week the heat pump portion quit working , I called " the guy " and he determined the temp sensor is kaput and a new one has been ordered it will be in next week. Temporarily he has wired the system so just the furnace comes on so we have heat .

I want to limp this system along for three more years and then I will replace all of it . He suggested going away from a dual fuel as it adds cost and complexity . Instead he said go straight heat pump with back up heat strips . He said a year ago he did exactly that at his house with a Tempstar branded unit and he is very happy with the performance and his electric bills are 200 a month regardless of winter or summer .

He said the modern heat pump around 18 SEER acts much like a mini split so the compressor is variable . I love my mini split in my man cave so this sounds attractive to me . We are in Georgia so hot humid Summers and mild winters with the worst temps in the high 20's which is rare.

Sorry for the long winded post but wanted all the details out there for comment. So any of you guys recently gone with a straight heat pump ? I am thinking in 3 years I might be able to get a 20 SEER which is the same as my mini split . I will keep the LP for the cooktop and water heater .

[billybek]

Go with whatever energy source is most economical to purchase.

Some of the heat pump systems that I have read about have more going on than meets the eye. Ground source heat pumps are an attractive option and the ground never runs out of heat during low ambient conditions. You may still reach a balance point where the heat produced by the heat pump equals the load when there is a cold snap sent special delivery from Canada. That is when the resistance heaters contribute to the heat supplied.

Another neat feature is using the heat pump as a preheater for domestic water. Piped in series with the water heater raising the final temperature of domestic hot to supply to the faucets. Edit: this works during the cooling cycle.

Pricey to have a well drilled in some areas depending on soil type and initial cost may have a long payback period.

I like the idea of the variable refrigerant flow systems and the mini split manufacturers have got this pretty much nailed down. No reason that it cannot be applied to the split system/heat pump market too.

You might want to look into the possibility of installing an ERV on the system when it is changed out.

[BK911]

Not sure why he had to wire anything.
Most tstats have an emergency heat function which turns on the aux heat.
With a heat pump, you need dual fuel in colder climates.
Either ng, lp or elect.
Elect is usually the most expensive yo operate.
And if not currently wired for it, you will need to run some pretty big wires.
If you are already using lp for other stuff, I'd keep it for emerg heat.
If no other appliances use lp, I'd still keep it for emerg heat.
My house has ng back up.
Would never consider replacing with elect heat strips.

[JackDidley]

Originally Posted by BK911

Not sure why he had to wire anything.
Most tstats have an emergency heat function which turns on the aux heat.
With a heat pump, you need dual fuel in colder climates.
Either ng, lp or elect.
Elect is usually the most expensive yo operate.
And if not currently wired for it, you will need to run some pretty big wires.
If you are already using lp for other stuff, I'd keep it for emerg heat.
If no other appliances use lp, I'd still keep it for emerg heat.
My house has ng back up.
Would never consider replacing with elect heat strips.

^^^ This makes sense. I have a heat pump and a gas furnace. Thermostat switches from HP to gas based on run time. I generally just turn off the HP when we start gettin 20° temps. No heat strips for me.

[Sooner or later]

I agree with BK

[rfuerst911sc]

Had to rewire because this Nest thermostat does NOT have an emergency heat setting . I looked and so did he couldn't find it . The LP portion of the dual fuel comes on when the temp sensor tells it to . With a defective temp sensor nothing was telling the gas to light .

I guess when I am actually ready to purchase a system I will see what is considered " good " at that point . A heat pump that works like a mini split with LP backup might be perfect . Thanks guys

[legion]

I lived in Georgia for the winter of 2014/2015, when it actually got and stayed below freezing for over a week. Heat strips are fine when they run a couple of times a year to bring the temp in the house up, but are ridiculously expensive to run continuously. Further, if the outside temp gets and stays below 20º for any length of time, they won't do a great job of heating your house any way. I remember people I knew with heat strips have indoor temperatures drop into the 50s and getting power bills in the $600-700 range after that winter. I had a natural gas furnace and got through the week just fine and only paid a little extra.

My advice? Call a different HVAC tech.

[Superman]

Originally Posted by legion

Call a different HVAC tech.

Agreed. My preferred setup is exactly what you already have, but for a smarter thermostat/control unit. HP with flame heat backup.

[rfuerst911sc]

In my opinion there is no reason to change HVAC guy he has been good so far and has 20 years experience . This was just a suggestion by him , he would gladly sell and install a more expensive unit . The Nest thermostat was installed by previous owners and not my choice . Any new system will go with a different thermostat.

I will say the mini split in my man cave works fantastic and is an energy miser . The garage is 24x26 with 12' ceiling , walls are 2x6 with fiberglass insulation and I have R19 in the ceiling . Running the mini split 24/7 for a full summer and winter it averages $20.00 - $25.00 a month to run .......... that is cheap !!!

[beepbeep]

As long as outside air temp is higher than ground water temp you might get from the well, air/water heat pump is more economical than water/water (using a well or plowed circuit).
We installed water/water geothermal heat pump 7 years ago and never looked back (170m well). Ours is on-off type but new pumps have VFD drive so they are able to "throttle" compressor somewhat. (at low loads they still do on-off regulation though).
Usually, modern heat pumps have electrical immersion heaters as "backup". Our pump is able to produce ~8kW of heat by compressor alone. But if something happens to compressor or it runs out of capacity, 9kW electric heater kicks in in three steps.
So far, resistive heater was never needed. House stays warm in -4F using nothing but heat pump (whose compressor draws 1.4kW of electricity, rest is "uplifted" from the well).

[Bill Douglas]

Yes, heatpumps are great when the house is well insulated and you have double glazed windows.

[Sooner or later]

I have R79 in most of my attic.

[rfuerst911sc]

Originally Posted by Bill Douglas

Yes, heatpumps are great when the house is well insulated and you have double glazed windows.

House was built in 1996 so I assume insulated to at least the minimum of that time. All windows are Argon gas insulated vinyl . Attic has about R30 blown in fiberglass . In my opinion the house is insulated good but not great . Winter here is generally mild with a few bursts of damn cold . I have been happy with the performance of this 23 year old system and I will probably just end up replacing with a more modern/higher efficiency unit .

[john70t]

Originally Posted by legion

I remember people I knew with heat strips have indoor temperatures drop into the 50s and getting power bills in the $600-700 range after that winter.

My combined electric+gas runs about $70 summer and $160 winter. Only a couple times has it gotten over $200.
1400sq w/basement in MI.

I've invested quite a bit though in retaining heat:
-Energy audit for a couple hundred.
-Double pane windows and heavy curtains for the sliders at night.
-A foot of foam in the attic. Been thinking of adding more.
-Basement and 1/2 floor rim joists also have been foamed. Each can be 20% total loss.
-The previous owner put 4" foam sheet outside of foundation down to the frost line about four feet down.
-Two stage furnace. New 13 seer a/c run only when over 90ish. Floor fans are used otherwise.
-Basement hot water pipes foam wrapped. May wrap the tank as well.
-Spare rooms have grates turned off.
-Thermostat is usually 60-65 but I'll bump it to 67 occasionally.

Drafts and gaps are the first thing which should be fixed.

An infrared thermometer on a cold day and making a total blueprint will help find the losses.

[cabmandone]

Wait, you have a dual fuel system that doesn't have a thermostat capable of going to Emergency Heat which bypasses the ODTS and defaults to the furnce?

As for what system, your degree days would probably allow you to go with a high efficiency variable speed system with electric backup staged in as the temp drops below a balance point... but I don't see how that's any less complicated than a Heat pump and gas furnace. My thermostat controls everything. I set the balance point in the tstat, the outdoor temp sensor tells the stat when the balance point has been met and turns the gas furnace on. I'm not sure it gets any more simple than that.

[john70t]

You can get DIY slow-rise foam for the walls when cellulose settles and leaves a gap at the top:
https://tigerfoam.com/sprayfoaminsulation/order-products/spray-foam-kits/

I've personally only used the polyurethane stuff from HD so far:
https://www.homedepot.com/b/Building-Materials-Insulation-Spray-Foam-Insulation/N-5yc1vZbaxj

Caveats:
-This stuff will make you very sick from the off-gassing. Apply it with chemical mask in the springtime and leave windows open.
-It absolutely needs to be brought up to temp to rise. Put in bathtub for hours before.
-Distance from surface is important for chemicals to stick and mix: Too far away and it's like very expensive spray paint. Too close and it spatters and lumps.
-Expect over-spray which will be impossible to remove and will burn holes through finished materials.
-Prep first and use an entire kit at once. The nozzle will clog and the cans will cool down.

[fintstone]

For reference, I heat and cool 3 floors (about 6000 square feet) with and in summer, from around $200 to as much as $400 (in July and Aug if very hot). My system is about 7 years old and 14 Seer. I have good insulation but keep it cooler in summer and warmer in winter than most folks. I would guess that your climate/temps are about the same as mine. I plan to replace those units with the same (except higher seer) when they die.

Personally, I prefer electric heat as it is safer, reduces carbon monoxide problems, propane or oil delivery...and generally allows more options for remote control. Similarly with hot water heaters. As long as your area provides electricity at a reasonable cost. I installed a buried propane tank to run gas logs in fire place in emergency (one for each floor) as well as my cooktop/gas grill. Those use very little...still have half a tank after 5 years.

[VincentVega]

I'm a big fan of modern inverter heat pumps. Uses just enough juice, not on/off, and most have low ambient functionality. You pay for the features though. I have a similar setup as you but my aux heat is oil. I rarely use oil though, only true emergency. I supplement with a wood stove and a mini split. The center system fan keeps the house temp pretty even.

I would only use electric heat if you seal the building well and insulate very well. Operating cost/btu is high, even if you have low electric rates. If/when I have to replace my primary system its going to be a inverter type.

[Fischer_76_911S]

I am in Georgia too, just a bit north of you. I am also in the biz and very familiar with these set ups as I did a dual fuel 17 years ago with natural gas at my own house. I have no horse in this race as I don’t do work outside my county. Too busy and no need to add drive time.

I ripped out my perfectly working dual fuel system in Jan and replaced it with a Carrier 20 SEER variable speed compressor heat pump system. Ditched the gas furnace. No need in our area. These heat pumps run circles around single speed units. My bills are so low they are almost laughable.

How good is this Carrier?

I flipped the neighbor’s house a few years ago. 4,000 sq feet 2 story (partial underground basement) with one 5 ton dual fuel zoned system. At 8 degrees one night I went to check on the house as it was empty with no people or appliances creating “free” heat. The stat displayed heat pump heating, and I was baffled as to why it didn’t switch over to gas. I about burned my hand on the refrigerant line going into the indoor coil. I checked the status via the stat and it was only running 80%. It wasn’t even trying! From that night on, if possible, I skip the furnace and go with just the variable speed 20 SEER Carrier.

In our area, heating with a heat pump is cheaper, safer, and heat pumps don’t dry the air so much as to cause dry skin and nose bleeds if you don’t run a humidifier which will need constant maintenance.

My experience and advice only

[fintstone]

Agreed. There is no need for gas or oil furnaces down south. About the only time the electric heat strips ever come on at any of my houses with modern heat pumps is if I turn the heat up more than 3 degrees at one time which triggers the "emergency" heat. I have gotten rid of the oil and propane tanks at all my rentals as well. Heating bills have all gone down. I only keep propane at my personal houses to run fire logs or cooktops.