hairmetal: You are right that on a sunny day it can warm to 50-60F above outside. On a heavy overcast it might only warm 10F but even a moderate overcast can allow a nice warmup. My citrus does very well, potted or inground, with 30s at night and 50s by day. This is the same temperatures as the main citrus growing areas in CA. They won't grow all winter but the fruit ripens and tastes very good. So in zone 7 MD at least for citrus you won't have to heat during the day just keep it from freezing. If you are growing citrus as an ornamental, as many do, then you will need warmer to get that pretty growth all winter. If you decide to grow something that needs chilling you could grow it in a pot and get chilling outside. Citrus can take a lot of heat so take that into consideration on your greenhouse design. Potted citrus can go outside during the frost free season. Potting makes many senerios possible.

Ross A dual fuel system can be a very effective strategy for heating one's home. Here are a few things that you should consider. 1. a complete understanding of nat gas rates and electric rates 2. your area's winter climate 3. your home's insulation qualities 4.a look into the future as far as whether electric rates are expected to be more stable than gas rates. In general, I have found that an electric rate of less than $0.11/KWh can make a high eff heat pump very compelling. I am attaching a fuel comparison calculator. Keep in mind that a heat pump performs double duty both in heating and cooling so its life may be marginally less on a dual fuel system depending on a good maintenance program. Today's heat pumps are much better as far as comfort than those 10 yrs+ ago. Good luck with your project and decision. IMO Here is a link that might be useful: Fuel Comparison Calculator

Bid: Trane 1 Trane 4TWB4024*1000*xXB14 Heat Pump 1 Trane XR Series 5 AirTite Air Handler High Eff Fan model GAM5A0B30M21SA 1 Trane TCONT802AS32DA Vision Pro Programmable Thermostat 1 10 KW Heat Strips (32800 BTUH) 1 Complete System 5 yr labor warranty 1 Copper insulated lineset (5/8 x 3/8 50 ft) 1 Trane BAYSEN02ATEMPA Outdoor temperature sensor 1 light weight concrete pad (Tom can do this instead of being billed for it) 1 PVC condensate drain 1 Ductwork and trim package 1 Venting package (bath & utility fans, dryer and range hood) 4 labor to install complete system Bid: Carrier Heat pump: Carrier 2.5 ton performance 15 series (25HPA530H) Furnace: Carrier variable speed air handler with 10 kw strip heat & coil (FV4CNF003) Thermostat: Carrier performance series Condensate: line to outside Ductwork: transitions and modifications Ductwork: supply air with registers in the floor. Insulated in unconditioned spaces at 11 locations Ductwork: Return air with filter rille. Insulated in unconditioned spaces one location. Exhaust: vent the range, dryer, bath and whole house (does not include fans or roof jacks) Warranty: 10 years parts ( when home owner registers within 90 days) 10 year compressor, 2 year labor and 2 year maintenance. We have a bid coming from the Brennan Heating & Air Conditioning. They sell the Lennox. Yes, we live in western Washington. We get snow in our area sometimes up to 3 ft. We will have all electric utilities. All bids have to have duct work installation. Also, what is your opinion on comparison of the Trane, Carrier and Lennox? I've noted what you've noted about the Trane. Isn't the Trane show a 4 ton Heat Pump? The Carrier quote has a 2.5 ton Heat Pump? Am I looking at it correctly? I want to thank you both for your input. This is my first time looking at these heating systems. I'm learning a lot. Barbara

""""I did not mean for that to come across that I was able to do any type of HVAC diagnostics or repair. What I meant was I feel comfortable taking the panels off the units for cleaning. Sorry if it came across that way. Those gauges could have greek on them for all I know. :-)""" There's no need for being sorry!!! Clean it up and if that works you've saved some money and if it don't--call your AC man. All you've lost is some time and soap. MR HAVAC believes you should call in a plumber to flush the toilet when your finished. Bob Brown is his personal kicking boy and must have not said anything lately and Mr HAVAC was getting shakey and needed someone to unload on and you were it. By the way, MR.HAVAC does give great advice, some of the best on this forum, but save your being sorry for when he really-- really lites into you.