Dual Fuel HP matchup with 80% Gas Furnace

[martlet]

Last year after much research I was set to order a Bryant dual fuel HP to work with an 80% efficiency gas furnace which is still in very good working order. The air handler and furnace are in the attic and will require flushing the lines to switch to the new coolant.

After installing new equipment on 1st floor (Rheem Mod furnace and Rheem scroll AC) we had exhausted our funds so now I am revisiting the choices. Athough I am very happy with the Rheem equipment in the downstairs, I was hesitant to select an outside Rheem dual fuel HP as a companion to the attic located gas furnace due to the complexity of the system. My reading revealed that the Bryant was an easier arrangement for the consumer to operate. Has anything changed in this respect? Has the Rheem dual fuel HP become easier for the consumer to operate?

Thanks

Scott

Lilburn GA

[lbf]

Typically, the thermostat is what controls the duel fuel system. We like Honeywell's Pro 8000 line of thermostats, they are very easy to operate and the balance points can be set right on the stat.

[BaldLoonie]

Can't get much easier than the Vision Pros.

Personally I'm impressed with the new RPNE 13 SEER pump. Tech just came from one, locked out on low pressure. HO admits huge snowdrift had buried it. Most boards wouldn't have protected it like that. Even with a low pressure switch, it would have just cycled on & off like a turnsignal as pressures dropped then equalized. The new Quiet 80s are a great, easy to work on reliable furnace.

[Wethead]

VisionPro 8000 controlling dual fuel... 92% nat. gas condensing furnace ignores "g" circuit call from stat during approx. 1.5 minute warm-up (actually more like a minute since the furnace doesn't kill the blower immediately).
Is there any problem or potential for damage to HP since it is defrosting for that first minute or so with no indoor blower running?
From what I can tell, the easiest way to keep the blower running throughout is to use the cont. fan feature which would keep it running at the lowest blower speed and switch to low fire speed after warm up time is complete, but I personally don't want my blower running 24/7.

[BaldLoonie]

If you have a brand that kills the fan on furnace startup, constant fan won't change that. As you said, the furnace ignores G during that period. Doesn't matter whether your DFK is a Vision Pro or an old clunker.

I don't think it is a biggie to run in defrost for a minute with the fan off. Takes more than that for the pressures to get switched around.

[Wethead]

I don't think it is a biggie to run in defrost for a minute with the fan off. Takes more than that for the pressures to get switched around.

Thanks, I'm running ICP's 92% two stage furnace w/ 13 seer single stage HP. I wanted their newest variable speed model which has a more flexible blower control board (that doesn't kill the fan on heat call) and supports two stage cooling but for some reason availabilty was low and I didn't have time to wait. But that being said I've installed 4 or 5 systems identical to the one in question and they are performing outstandingly. I'm in NE Pennsylvania where we've had some frigid weather in the last month and my customers have said the heat pumps are keeping up well all the way down to the 20* balance point I set them at.
Is my understanding correct that the VisionPro 8000 when set up for fossil fuel back-up will not allow furnace to run as aux heat before the balance point is reached at which time HP is locked out? If so, do you think I should raise that balance point a little to compensate for those days when high winds with cold temps might lower heat pump capacity? Thanks for the reply.

[BaldLoonie]

The 8320 will not allow backup at all. The IAQ will if the temp drops 2 degrees from setpoint and you are within HP lockout and gas lockout points. The IAQ also does a lot of other neat things, worth it in my view.

Lowest we can get by with around here is 30 or pumps alone won't keep up. We size the outdoor unit for cooling. If we set them to shut off at 20, we'd have every customer on us.

[Wethead]

If the A coil is upstream of gas heat exchanger will it be able to reject heat into the hot air crossing it? Is that the reason IAQ

[Wethead]

Sorry, question cut off... I was asking if that is the reason IAQ uses 2 degree droop? But nevermind that part, I just comprehended your reply. I still wonder about A coil's ability to reject heat into warm air stream. It seems to me it makes better sense to run either or if warm air inhibits heat pump performance. I appreciate your input and do understand what you stated about sizing to the cooling load. I trust the science but when I'm coming home from working outside in the heat on a 100 degree day I want my house to feel like my fridge (even if that is only 2 days out of the summer). I'm not just a member of club oversize, I'm club president. (ha, ha) Seriously though, I don't have a problem going 1/2 ton over. Please let me know your thoughts on the A coil/ heat exchanger issue. Thanks

[howardair]

A heat pump coil MUST ALWAYS be downstream of "auxiliary" heat. Otherwise High head pressure WILL result.
In a "Dual Fuel" situation IE: gas furnace w/heat pump. An OD stat is normally used to prevent both from working at the same time.

[Wethead]

Thanks, I knew the coil must always be downstream but the only reason I ever heard given was because of moisture entering furnace heat exchanger when cooling. Yes, the VisionPro stat uses an outdoor stat to control dual fuel. I just wasn't sure about running both heat sources simultaneously. Thanks for the reply. I'm going to raise my balance point. Thanks