Who did the heating and cooling load calculations? It seems odd that the cooling load is 52K BTU but the heating load is only 61K BTU. What is the size of the house? What are the typical winter lows?

The back up furnace should be a variable speed model, but I think the Infinity 98 is overkill. The Carrier the 59TN6 or the 58CVA would be fine. These have AFUE ratings of 96.7% and 80% respectively.

Any gas furnace would have to be an Infinity fully variable speed blower.

Howeverâ¦

Regarding an all-electric FE series fan coil unit, if the backup electric elements are individually breakered, then by shutting off all but the 5kW element may allow your generator to handle the heating load during an emergency situation.

How many kW is your generator? Might be less expensive to upgrade the generator (if you even need to) than to install a gas furnace after you calculate the furnace, propane tank and venting.

IMO

SR

It would seem to me that a Greenspeed would be overkill for coastal VA since it rarely gets below freezing there.

I would also think that the Trane would last longer in the sea air.

All good posts and OP should take them to heart. While the OP says this is a coastal Virgina location, I looked up the average winter temp for Virginia Beach which is low 50s. The GreenSpeed is definitely overkill for this location. If you want a propane generator, that's fine. But I would size it for all electric and forget the propane backup furnace. And the load calc needs to be redone by another party for comparison purposes.

IMO

Thanks all. I'm on the Eastern Shore with winter average lows in the 30-40 range though of course sometimes it gets into the 20s and teens. My existing propane powered Onan generator is rated at 7kw for continuous operation. I was told by the Carrier contractor that substituting the propane furnace would be cost neutral to me. As to back-up heat, I'm more concerned with outages than super low temperatures as I'm expecting the H/P to handle the vast majority of the heating needs.

The load calculations were done by the Trane contractor who works in this area. There are only two HVAC guys here - one does Carrier, the other Trane. The Carrier contractor did load calculations when the old system was put in 15 years ago. He told me his heat load calc from back then was a little higher than what the Trane guy said but I didn't ask for a number.

I did also get a proposal from the Trane guy as follows: 4TWZ0060A1000A H/P with TUH2C100A9V5VA Furnace, 4TXCC008CC3HCB coil and a TCONT803AS32DAHP control. Both contractors gave other alternatives with lower efficiencies.

I like the Carrier quote because I know that guy's work first hand and I like the idea of being as efficient as I can. Perhaps the later is costing me more than is appropriate for my climate.

I didn't know that Trane holds up better in a coastal environment. Is there a comparative measure of corrosion resistance between the two brands?

I would still suggest the Carrier Infinity Greenspeed with the FE series fan coil, purchase a 10-year labor warranty and annual service contract so that you have peace of mind for 10-years with the highest energy efficiency todayâÂÂs air-source technology can provide.

Being an inverter variable speed compressor might mean that your 7kW generator will start the HP on low stage. You might also want to verify that your generator produces clean enough A/C (alternating current) to do the job without damage to the HVAC equipment (very low harmonic and hash output) but of course you should still have the 10-year part & labor warranty.

I always suggest the installation of âÂÂWhole House Surge Suppressionâ installed at the load center as well. The manufacturer should verify use of this product with a generator; it can be switched Off if itâÂÂs not advisable for use in conjunction with a generator.

IMO

SR

Here is a link that might be useful: SurgeBreaker Plus

fsq, I've asked the Carrier contractor about selectively shutting out heat strips (or maybe only having one 5kw heat strip) and limiting the higher stages on the condenser using the fancy controller that Carrier has based on your comments. He's checking on that which would indeed provide a solution to running the all electric unit during outages. If this isn't possible, should a propane furnace rather than a fan coil cause significant concern?

Your suggestion on surge protection is also appreciated. Am I wrong in thinking that installing the unit to which you linked is accomplished merely by connecting it to a new circuit breaker in the panel?

I still am a bit concerned by the comment that Trane equipment would hold up better than Carrier in a coastal setting. Is there any further insight on this?

Also, despite fsq's endorsement and my own bias toward the higher efficiencies in Greenspeed, tigerdune, who is a most knowledgeable contributor on this forum, has said it's overkill for my climate. I'd rather not pay more upfront than I'll ever get back in heating cost savings over the life span of the equipment. A bit excessive would be OK, but wretched excess, maybe not. Any more thoughts on this?

The Greenspeed equipment is pricey. You should get a quote on Carrier's best conventional heat pump and calculate how much more the Geenspeed would cost. Then you need to calculate your average annual heating and cooling costs and estimate how much money you will save each year if you upgraded to the Greenspeed. You live in a relatively mild climate area, so the return on investment could be past 20 years. If that is the case then the Greenspeed would not be worth the investment.

Since you already had propane furnace, getting another furnace to replace it is not necessarily a bad idea. What are your propane and electricity costs? This will determine whether all electric or propane back up would be more cost effective. I think in your case you will hardly ever use the propane furnace since the Greenspeed can work well below 20 degrees. I would think in a power failure in the winter that you only run the propane furnace and would not waste any power generation on the heat pump and electric strips.

Trane makes condensers and heat pumps with a special coating for installation near salt water. How far are you from the shore? If you are not very close then I would not worry about it.

Regarding breakers for the backup, it seems to me that there is a provision to add individual breakers in the FE fan coil unit which would mean that you could switch off all but the 5kW element - but let your contractor tell you that, IâÂÂm just some âÂÂguyâ on the Internet.

An Infinity propane furnace properly installed with the natural gas to propane kit and properly vented should not be a concern beyond the cost of propane. Be sure you have working smoke & CO detectors in your home!

You are right regarding the connection of a âÂÂWhole House Surge Suppressorâ unit. It will require space for a double 30-amp breaker in your main panel. You should be left with adequate free space in your load centre after the installation is complete for future use. You can protect your large screen TV etc. with a âÂÂMonsterâ type power bar having surge protection but how else can you protect your large investment HVAC system that runs on 230v? This equipment also has sophisticated electronics in the HP, furnace or fan coil and T-stat. This device will help protect EVERYTHING from surges originating from both inside and outside your home. YouâÂÂve mentioned you have a generator so you probably have electrical anomalies in your area. This device is cheap insurance and may save you from headaches as it reduces the stress on all sensitive electronic equipment within your home. It should also come with its own insurance (up to $50k) incase something fries on its watch within the warranty period.

Regarding coastal locations I have to say that my experience is limited as I live on an inland island (Montreal) in a cold (and sometimes hot) climate. So again IâÂÂm just some âÂÂguyâ on the Internet. However, many of the internal components in either a Trane or Carrier HP may come from the same group of manufacturers. None of this stuff is Mil Spec designed to operate at sea or on Mars so I donâÂÂt see a huge difference. If Trane has a âÂÂspecialâ coating on the exterior âÂÂskinâ so does Carrier, âÂÂbaked on powder paintâ etc. The truth is itâÂÂs all going to Hell regardless of what any salesman tells you. My experience is such that if this is a real concern then the best solution is geothermal. It operates within the conditioned envelope of your home and is never exposed to outdoor elements, other than flood or fire, the way air-source equipment is.

As to whether Greenspeed is overkill I disagree with those that say it is. You mentioned temperatures into the teens. That makes Greenspeed a great choice, 13-HSPF. The only place energy costs are going over the next 10years is up. Energy efficient equipment capable of running at lower speeds should mean less wear and a longer life cycle.

Real world analysis weâÂÂre seeing here after at least 1-year of operation is that Greenspeed is closing the gap with geothermal in a meaningful way, even in...

Thanks to all for the follow-ups especially fsq for taking extra time to explain his views.

Greenspeed is indeed pricey. The delta in price from best conventional to Greenspeed is almost $5k. I'll need to save on the order of at least $6k in energy costs over 10 years to come out even. There are of course intangibles to consider.

I need to navel gaze for a bit.

I read your previous posts again. You stated your generator is rated for 7KW at continuous operation. This generator is not large enough to power a 4 or 5 ton Greenspeed condenser and an air handler with electric strips. Did the contractor explain this to you?

I don't think it is possible to pay back the extra $6K in a 10 year period. Do you know your annual heating and cooling costs? When you have them we can calculate some possible scenarios of potential savings. I think the pay back period of the Greenspeed is over 20 years.

My suggestion is it to get Carrier's best 2-stage heat pump with the 58CVA variable speed furnace and set it up as a dual fuel system. Use the furnace only during a power outage. Use the extra money you have saved to buy propane to heat the house when needed for the next 10 years.

Regarding the use of a generator and the Greenspeed HP, it may be possible to use a 7kW generator in this case as the Greenspeed is different from a conventional single or 2-speed compressor unit. Whereas the conventional condensers represent a virtual dead short across the AC line when first switched on for the first cycle or so of AC (alternating current), the Greenspeed is inverter controlled with Variable Frequency Drive (VFD). That may mean that the compressor in the Greenspeed, as in all inverter controlled units may represent a higher impedance at the outset of startup and not the virtual dead short of a conventional compressor.

If the HP starts full tilt and then ratchets down then all bets are off. If the HP can start slow and ramp up then bets are on. I would want to consult the Carrier technical or engineering department directly on this matter. I would also ask Carrier how âÂÂcleanâ the AC produced by a generator must be for safe, reliable operation of all sensitive circuits. Your dealer might also provide an answer if he can monitor an existing installation measuring the in-rush current of a similar sized unit with a âÂÂTrue RMSâ reading Fluke or similar clamp-on ammeter measuring peak current of 100-ms (milliseconds) or less. The meter must be âÂÂTrue RMSâ reading for accuracy, otherwise harmonics and other components that compose an AC signature will not be read or factored in.

I hope this explanation helpsâ¦

SR

The Greenspeed product data sheet shows the rated load amps as 27.0. So if I assume 240 volts and do a simple calculation ignoring phase angles and losses I come up with 6480 Watts. There may be enough power left over for the air handler and heat strips, but nothing else in the house.

Thanks again for everyone's thoughts and insights. I ended up with the GreenSpeed heat pump and a propane furnace. Finding a way to make things work with electric elements just wouldn't pan out with my concern about electrical outages and my existing generator.

I'm very happy with the new system. Very quiet both inside and out. The internet connection to the thermostat is also nice though I'm not sure it will ever be more than a gee whiz thing.

Time will tell if energy savings will be significant and whether the coastal location will do bad things to the heat pump. The 15 year old one it replaced didn't look too bad so I'm hoping the new one will be at least as good as that. As I write this, it's 33 degrees with about a 20 knot wind and the air coming out of the registers using the H/P is actually warm! Already that's a change for the better.