a/c & gas furnace vs heat pump with gas backup

15 years ago

I have to replace a 2.5 ton a/c & gas furnace. Heating load done =23,228 & cooling load = 27,206. 1500 sq ft ranch with small room over attached garage. I live in SE VA with relatively mild winters & sometimes hot summers.

Gas for this month was 39.97 for 14 ccf and electric is 7.32Â¢/kWh jun-sep and 6.69Â¢/kWh oct-may.

I got estimate for 2 units:

York Affinity 3 ton a/c 15 seer, 80k btu 80% modulating gas furnace. Honeywell prog t-stat, lifetime warranty on compressor & 10 yr parts & labor. i believe he said it was a 2 speed a/c which I was told would help with short cycling. I wondered if this unit may be oversized, but I was told .5 ton is not that big a deal and the 2 speed would help with short cycling. Est. $6,942

York Latitude 2.5 ton a/c 14.5 seer, 80k btu 80% single speed gas furnace. same t-stat, 10 yr warranty on compressor, 5 yr parts, 1yr labor. Est. $5,437

Then I was told by someone i know that I should look into a dual fuel system-- heat pump with gas furnace back up.

I got an estimate from another company for Amer Stand 80k btu 80% 2stage variable speed gas furnace with 36,00 btu 14 seer heat pump condenser w prog t-stat & new tubing. Est. $7,231.83.

Also, est for 80k 95% 2 stage variable speed gas furnace with 36k 14 seer a/c condenser (is this supposed to be compressor?) with new tubing. Est. $8,110.99.

Now I don't know what to do. The 2nd estimate seems way too high, but I'm not sure what would be best for me.

Sorry about the long post, but any suggestions? Pros & cons?

Comments (6)

ryanhughes
15 years ago
Based on the information you've provided, sounds like the York quote is the best option, but I don't agree with the 80% modulating furnace. That's a high-end furnace, and going with the 80% version doesn't make sense to me, especially in our region where it can get cold at times (I'm in Maryland). Is PVC venting an issue? The York Affinity is a nice line of equipment. American Standard isn't bad, either, but the equipment that the York rep. is quoting is better in my opinion. 3 tons is a bit much for your cooling load, but it's what you'd have to go with if you went with the Affinity line. The 2.5-ton Latitude unit would be the better fit. With the low stage on the Affinity approximately meeting the cooling load at design conditions (which won't be met on all days), I don't think you'll be getting those long run times that you should with a 2-stage system. Ask the York rep. if he can quote the CZB or YZB 2.5-ton single-stage Affinity unit with a 90+ efficient v/s furnace (modulating or 2-stage). Not sure where the American Standard rep. came up with his sizing. Do you like it cold in your house (68-70)? Did the York rep. do the load calculation?
ryanhughes
15 years ago
Also, are you sure about your heat loss (heating) value? 80k is way oversized for your heat loss if what you have is accurate.
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I'm leaning towards just heat pump with heat strips. That should be fine for your area. If you plan on keeping it that warm in the house as you say in your OP, I would get the Bosch Inverter heat pump as it produces heat clear down to about 5-6 degrees ambient and very efficient at what it does. Then use the strip heat as you need it. I don't know that you'll find a contractor though for this for a new construction job as Bosch just recently came to the Houston market a few months ago. The distributor network for Bosch is in it's infancy... so there are pros and cons for choosing this brand. For what it does / how it does it --- it's a game changer for my market. (Katy, Texas area) As a comparison --- an average run of the mill single speed heat pump will probably struggle once temps drop into the 20's for any significant amount of time. They are efficient when compared to strip heat (utility bill cost wise) but there are higher limitations with those. I've gotten email notifications from my electric provider that they are estimating my next electric bill at less than $50 for November. This may wind up being my lowest electric bill ever for my power rate of 12 cents per KWH. With that said, I keep it quite chilly during the winter and my house is all electric (no gas at all). I shut it off at night and really just use it to take the chill out of the house in the morning. If it gets really cold here, I will probably just heat the main part of the house over night --- as I have it attached to a 4 zone duct system. (This is to explain the how and why my electric bill is so low -- design of the HVAC system is a big part of it.)
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liborn
Original Author
15 years ago
I don't know where the Am Stand rep got his sizing either. I know the 95% is much more efficient, but I don't think the budget will allow 8 grand.
I don't keep my t-stat that low in the summer, more like 76-78. And, yes, the York rep was the only one who gave me a printout of the load calculation.
ryanhughes
15 years ago
Tell the York rep what I said about the sizing and cycling and see what he says:

1. If the heating load isn't even 30k btu, why is the 80k furnace being quoted? The 60k would be a better match and still be oversized. I've never seen a heating load less than a cooling load--not saying it can't be possible... I'd want to make sure the calculations were correct.

2. The Affinity 15 3-ton unit is a 2-stage unit. First stage would be around 75% of the full capacity. That's 27k btu's, which is about what your load is. The load is at design conditions, which is when the temperature outside is "extreme." That means that the unit will most likely cycle a lot in low stage, removing less humidity and costing more to operate. I would bring this issue up with the dealer and see what his opinion is. The 2.5-ton 13 SEER Affinity might be the better choice.

Also, I recommend that you get the Honeywell VisionPRO IAQ thermostat and have it setup for dehumidification on demand. I also suggest the 90+ efficient furnace. Not sure why the 80% was quoted. Maybe PVC venting was an issue.
liborn
Original Author
15 years ago
He never mentioned pvc venting, but I'll ask. Do you think I should bother to ask about the dual fuel system, or just go with the a/c & furnace?
ryanhughes
15 years ago
With those electric rates, a heat pump would be economical to heat and cool. It's worth asking in my opinion. I'd be more focused on the sizing issues I've mentioned above though. Sizing is a very important factor in any installation. The good thing about the modulating furnace is its many steps of heating--1% increments from 50% to 100%. But a 80k is still oversized for your heating requirements assuming they are accurate. Double-check on the heating load with the company.

Important note: There are two York modulating furnace. One does NOT have the variable-speed blower. Make sure the one you're getting does. It can provide better dehumidification and is better with two-stage outdoor units.

I know there's a lot of info for just replacing your HVAC equipment, but getting it right saves you a lot of trouble in the long run. Just read some of the horror stories some people have had from poor installations and oversized equipment.

a/c & gas furnace vs heat pump with gas backup

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a/c & gas furnace vs heat pump with gas backup

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