Gas and Oil Home Heating Furnaces - 2 HVAC untis due to new addition

I live near Orlando, Fl. in a 20 yr old split level house of 2000 sq ft. We relpaced our gas HVAC appr 8 years ago. The previous system (2ton?) did not seem adequate but due to the undersized duct work, the installer only increases the size of the unit a 1/2 a ton (2 1/2 ton).

We just adde 600 more sq ft on to the side that was a siigle level. The contractor decided it would be best to add another unit (heat pump) for the 600 sq ft, plus sized it for an addition 700 sq ft for the single level also, thus assiting the original HVAC.

When you have two units in a house, should the duct work for each system be completely separate or would they both feed the same single duct work? If they can use the same dict work, shouldn't they work off of the same thermostat so that one blower is not on when the other is?

Karl
Orlando, FL

You say one unit is gas and now they want to put a heat pump in the other unit????????I say stay with one or the other.First look at the $$$$$$ here. I dont see where you will get back the cost of the heat pump down here in Florida.Im in west palm We use electric strips and A/C only. Just an AC cost a lot less than a heat pump.I dont see why when you put in the 2 1/2 ton the guy should have reworked your duct work then.If you go with two units no the duct work dont tie together and you should have two t-stat so it will work like a zone.Not seeing the job or lay out.Id say for 2600sq ft here ,go for a 3 1/2 ton AC one unit with electric strips in it and rework the old duct work.If you think about it you dont have the heat on that much down here for a heat pump to pay.;) ED put R30 in the attic and lots of vents ok

From your post I have to assume you have conventional a/c with gas for heating. Its a 2 1/2 ton on ductwork sized for 2 tons, feeding 2000 sq. feet of split-level. You've added 600 sq. feet and the contractor wants to size the system for 700 sq. feet with a heat pump. I hope I'm right so far. First off, unless you have a whole house heat load run and revamp and resize all the ductwork for one single system, you're going to have to keep the new units duct system seperate and with a seperate t'stat and electrical system. Offhand, I believe your existing system to be undersized, however if its been satisfactory for the past 8 years, you can't argue with that. As for an air-to-air heat pump for the addition, go for it. It will cost you more but you will have one of the more efficient forms of heat for this area. Since you can't use your existing gas for backup heat, the HP will have booster electric strips in case the HP can't keep up . The HP alone should be able to keep you comfortable down to the mid 30's. Straight electric strip heat is basically trouble free and gives you good heat, as long as you pay your electric bill. With a HP it would only be used for emergency heating. Here in central FL., HP's are common and I believe Fla. Power or your utilitiy provider will give you some up-front cash. Hope this helps. Good luck.

Dont see a heat pump down here in FL that far south.Had heat on 3 days last year. Year before 1 week.Heat pumps are about all we sell and install up north and I do like them but not here.Put the $$$$$ in the bank, thats the way I look at it ;) ED

Thanks for the replies. Some clarification:
The original house is 2000 sq ft and we added 600. The original HAVC was conventions A/C with gas furnace. The A/C struggles to keep the house at 78 during the 90+ degree weather, but does do it by running most of the time. There the thought was to have the heat pump not only service the new 600 ft but to also do 700 of the exisitng, therefore it was sized for 13 sq ft. That should allow the existing A/C to manage the remaining 1300 sq ft of the 2 story part.

I talked to the contractor today. He is going to split the system. He just has not got to it yet.

Hopefully the heating strips will not be used much. It does get down into the 20s several times a year. One year it hit in the teens, but that is rare. The addition was built for my wife's mother who seems to like it closer to 100 degress :<). The 600 sq ft is a bedroom/bath for her plus an additional eating area and pantry off of the existing kitchen. It is going to be a challeng to adjust the registers so that she can keep her room several degress warmer than the rest of the house. We probably could have got my with just a conventionsl A/C and used base board heating in just her room, but some day the room will likely be our master bedroom so the heat pump looked like a better route. Plus I guess we got a break in the unit. Got a SEER 12 for the price of a SEER 10, because of a small dent.

Thanks again for the info.

Ed, I have to agree with you that in south FL where you are, heat pumps probably are an overkill. I fact the further south you go the fewer heating systems you'll find. But here in central FL, away from the warm gulf stream, it can get dang right cold. Afterall, keparks has a gas heating system so somebody decided it gets pretty chilly round here.

http://www.firstco.com/faqua1.htm

This would be an ideal situation for firstco's heating system.
It uses the heat from an existing gas water heater.
Much cheaper than a furnace OR heat pump, plus gives you warm effiecint gas heat.

Ok you have gas on one unit Id stay with gas also on the new unit and AC .Ill bet MOM MA INLAW Wont like the cool like air that you will get from the heat pump;) ED

Originally posted by Ed Imeduc
Ok you have gas on one unit Id stay with gas also on the new unit and AC .Ill bet MOM MA INLAW Wont like the cool like air that you will get from the heat pump;) ED

You know if your AC runs that much on the old one you can get a heat recovery system put on it . That would kick up your SEER
about 2 points and give you free hot water. Have one on mine turn the elec. hot water off and had all the hot water I wanted at about 140 temp for the 8 months run off the AC