Options for new HVAC system

[Z3Dreamer]

Option 1 is to replace existing equipment with new coil, and furnace. They would not replace our existing a/c unit.

Option 2 is to replace coil and furnace and add a heat pump. Obviously, this option is a few thousand bucks more, but will save us propane on those days when it is just a little cold. It is not meant to save fuel on those terribly cold, windy days we have in the NC mountains. In other words, I would have a heat pump and an a/c unit.

Would like to know if those who have Option 2 are happy with this.

 

[frank]

why would they not replace your a/c unit? a/c units are being used everywhere I know of in the midwest.

 

[sengsational]

There's not enough info here to do the financial break even calculation, but I suppose people can talk about the comfort aspect. Or another aspect is if you're annoyed by paying the high dollar rate when they fill the propane tank. My FIL had a rented tank and could only use the one supplier, who had a much higher rate per unit of fuel. He got so steamed, he had them come and dig up their tank, and went with a heat pump.

 

[REWahoo]

Are you factoring in the $2,000 tax credit on the heat pump?

 

[wmc1000]

Our 2800 sq. ft. home is heated and cooled with our 3.5 ton heat pump. Electric backup coils in furnace kick in around 30 degrees. The new high efficiency heat pumps can produce heat well below zero.

I have a 2 ton minisplit heat pump in my 1800 sq. ft. 12 foot high barn which is way undersized and one night early this year it was -9 degrees and the barn still maintained a 63 degree temperature. Last year on a -5 degree night it held it's normal 68 degree setting with no problem.

 

[ncbill]

Did the same down here in the Piedmont.

Original central A/C unit with gas furnace was replaced with a newer gas furnace & heat pump.

However, we have cheap natural gas instead of expensive propane.

But just a couple of years later I stopped using the heat pump in the winter to save wear & tear on the compressor & have just been using the gas furnace for heat during the winter.

If the OP has access to cheap TVA electricity where they are they do sell configurations where the heat pump can have both electric resistance strips (again, for use with cheap electricity) & a gas furnace as backup...in combination, the electric strips allow the heat pump to perform better at lower temperature...it's not just pure resitence heat.

 

[Music Lover]

why would they not replace your a/c unit? a/c units are being used everywhere I know of in the midwest.

Maybe the existing one works perfectly well and doesn't need replacing.

 

[38Chevy454]

I'm out in the country without natural gas. I have heat pump A/C with propane backup. My switchover is set for 25F. mainly because of the comfort factor of nice warm air out the vents vs just a bit over room temp. Propane is certainly more than nat gas cost, so if you have nat gas available the economic justification of the heat pump may not be as great. One thing you might get is a SEER improvement with a new A/C system vs just replacing the coil. Efficiencies are mostly gained in the outside compressor/condenser unit, and a latest design may be higher energy efficiency than your current.

 

[Z3Dreamer]

OP here. A/C unit works fine. No need to replace. I don't have access to TVA electricity or natural gas. Just propane and electricity.

As far as I can tell, maybe 38Chevy454 or NCBill have the setup I describe as Option 2. Contractor wants to do Option 2 which will leave me with a coil, a furnace, a heat pump and an A/C unit. I have never heard of having both a heat pump and an A/C unit so I asked y'all. Looks like neither of the two with a similar system think it is a good idea.

I would get the SEER level recommended by the contractor which is an improvement, I just don't know that a heat pump is a useful thing in the mountains of NC. I am sure it is more efficient, just don't know that the payback period justifies it.

 

[REWahoo]

I have never heard of having both a heat pump and an A/C unit...

Nor have I. My understanding is a heat pump is an A/C unit that is able to "run in reverse" in cold weather to provide heat. At least that's what mine does.

 

[Masquernom]

My sister's house has a heat pump for heating and cooling. Instead of electric resistance heaters for emergency heat, she has a propane furnace. One nice thing about this arrangement is she also has a propane heater that works without electricity, so she has heat after storms if she loses power.
There is no magic to using a furnace in place of electric resistance heaters for emergency heat with a heat pump. It probably just costs a bit more during installation.
The main reason I hear for doing that is when it's very cold, people prefer the much higher temperature air output of the furnace over the heat pump.

 

[Z3Dreamer]

So far, no one has a furnace, a heat pump and an A/C. The contractor said that having the heat pump for heat would lower our propane cost, but we know it will drive up our electric bill. Will have to decide whether the decreased fuel cost is worth the upfront costs.

 

[Masquernom]

So far, no one has a furnace, a heat pump and an A/C. The contractor said that having the heat pump for heat would lower our propane cost, but we know it will drive up our electric bill. Will have to decide whether the decreased fuel cost is worth the upfront costs.

A heat pump is also an AC unit.

 

[Z3Dreamer]

A heat pump is also an AC unit.

I understand. That is why I am asking. When the contractor is done, I will have a furnace and a heat pump AND and an A/C unit. Currently, I only have a furnace and an A/C unit.

I am trying to find out if anybody has such an arrangement.

 

[tizod]

AC + Heat Pump

Z3 it seems silly to have AC and HP unit. If you need this for heat, I'd remove the AC and use HP+propane+electrical local heater per room to reduce propane use and HP for AC. In NC that is a good place for a heat pump as it doesn't get silly cold too many nights, so you can have it switch at 25 degrees or so and use little propane (since you use propane, and not a cheap alternative). The HP is way more efficient, but blows out rather cool air. So how you have your air outlets in a room matters (for instance, my wife hates HP until I redirected air flow away from her sitting chair). HP is more prone to breakage than AC.

So if AC works fine, keep it and supplment just heat (use electric).

As an engineer I never understood why they do not turn on or add electric boost for the outlet temp. They do that everyone would love the HP. (and make them more reliable).

I just put in new AMANA HP & electric furnace (subsidized electric here 3.3 cents/kWH). Five years running, working well. Prior HP's failed about every 8 years...

 

[Piper20]

If you purchase a decent variable speed heat pump air duct temperature will be 95-100 down to at least zero. We’ve had a VS heat pump since 2018, Carrier, that works great. The heat strips won’t come on till -5 F.

 

[Z3Dreamer]

Z3 it seems silly to have AC and HP unit. If you need this for heat, I'd remove the AC and use HP+propane+electrical local heater per room to reduce propane use and HP for AC. In NC that is a good place for a heat pump as it doesn't get silly cold too many nights, so you can have it switch at 25 degrees or so and use little propane (since you use propane, and not a cheap alternative). The HP is way more efficient, but blows out rather cool air. So how you have your air outlets in a room matters (for instance, my wife hates HP until I redirected air flow away from her sitting chair). HP is more prone to breakage than AC.

Good idea about NC weather, except I am in the mountains of NC with many cold nights.

I absolutely agree that it is silly to have an AC and a heat pump. The concept was proposed by a new estimator for an HVAC contractor that we have used for many years, so I thought I would throw it out to the group. Here is what the group has said: No one has such a system and no one has even heard of it. It is such an odd proposal that most think I am talking about something else.

So, I thank you all. I will tell the estimator to "Try again."

 

[ncbill]

Good idea about NC weather, except I am in the mountains of NC with many cold nights.

I absolutely agree that it is silly to have an AC and a heat pump. The concept was proposed by a new estimator for an HVAC contractor that we have used for many years, so I thought I would throw it out to the group. Here is what the group has said: No one has such a system and no one has even heard of it. It is such an odd proposal that most think I am talking about something else.

So, I thank you all. I will tell the estimator to "Try again."

Wait...do you currently have one HVAC system for the entire house or two?

Normally a heat pump replaces a central A/C-only outside unit.

Any gas furnace is built into the air handler.

With a typical configuration air is drawn in from the home through the bottom of the air handler up past the gas furnace's heat exchanger(s) (for heating) then over the coil (for heating or cooling) sitting above the air handler then to the ductwork then to the house registers.

 

[Z3Dreamer]

Wait...do you currently have one HVAC system for the entire house or two?

Normally a heat pump replaces a central A/C-only outside unit.

Any gas furnace is built into the air handler.

With a typical configuration air is drawn in from the home through the bottom of the air handler up past the gas furnace's heat exchanger(s) (for heating) then over the coil (for heating or cooling) sitting above the air handler then to the ductwork then to the house registers.

I have 2 zones. The zone for upstairs has not been part of this discussion. But, if I accept this proposal, I will have a heat pump for the upstairs, a heat pump for downstairs and an AC unit for downstairs. And a propane furnace that services the downstairs.

Yes, I understand the normal configuration.

 

[Samsung4321]

have a heat pump and an a/c unit.

Presumably the 'a/c' is cooling only, not reversible.

Air conditioning is heating and cooling - for reversible heat pumps.

A new heat pump might be heating only but much more likely reversible.

The difference between heating and cooling modes is simply the valve(s) that reverse the flow of the fluid after entering / exiting the compressor.

Little advantage to keep 'a/c' and install reversible heat pump - except for cooling redundancy.

'Not worth it':
https://highperformancehvac.com/converting-air-conditioner-heat-pump/

 

[ERD50]

... As an engineer I never understood why they do not turn on or add electric boost for the outlet temp. They do that everyone would love the HP. (and make them more reliable). ...

I assume you are referring to the lower outlet temperature of a typical heat pump system in heat mode? I've heard those complaints too, and it makes me skeptical as to whether I would be happy with one. I like the nice warm blast of air from a typical gas furnace. About 95F for heat pump, ~ 115F for NG.

But if you are heating 68F air from 68 to 95, that's a 27F delta, 68 to 115F is 47F - twice the delta.

So I think that means half the heating would need to come from resistive heating, which would really reduce the efficiency advantage of a heat pump. Even at 1/3rd, it's a big hit. I'm guessing that's why they don't do it?

FYI: 95F room temperature is considered the point where a fan (for cooling purposes) isn't really going to make you feel cooler - it's too close to skin temperature. So 95F from a heat pump vent is just around the point of cooling you, it doesn't feel warm at all.

-ERD50

 

[Z3Dreamer]

Presumably the 'a/c' is cooling only, not reversible.

Air conditioning is heating and cooling - for reversible heat pumps.

A new heat pump might be heating only but much more likely reversible.

The difference between heating and cooling modes is simply the valve(s) that reverse the flow of the fluid after entering / exiting the compressor.

Little advantage to keep 'a/c' and install reversible heat pump - except for cooling redundancy.

'Not worth it':
https://highperformancehvac.com/converting-air-conditioner-heat-pump/

Yes. I don't see the point of an A/C and a heat pump. Looks like no one else does, either.

 

[Masquernom]

I'd want a detailed explanation from the estimator about why he proposes both a heat pump and an AC unit. There may actually be a reason depending on the details of your existing installation. But it's not easy to envision.

 

[Z3Dreamer]

I'd want a detailed explanation from the estimator about why he proposes both a heat pump and an AC unit. There may actually be a reason depending on the details of your existing installation. But it's not easy to envision.

From his proposal: "The dual fuel(hybrid) option is one in which the heat pump runs the system until it gets quite cold(typically set at 35 degrees). At that point, the gas furnace takes over and runs the system. The dual fuel option gives you the savings of a heat pump in milder weather and also the intense heat of a gas furnace in colder weather. This option provides great savings on your gas consumption. The typical reduction in gas consumption is 50% to 70%. This is the most popular system we presently sell."

 

[Music Lover]

I think some people are missing an important detail. The installer is not proposing adding both a heat pump and an AC unit, he was proposing to add a heat pump and leave the existing AC unit in place.

That makes perfect sense to me. The AC unit works fine. Maybe it can be a backup, or maybe it can be used to help quickly cool the house on hot days, or maybe it doesn't get used at all. There's no harm leaving it in place, but there is a cost to remove it.