Heating, Air Conditioning, Fridge, HVAC/Type of heating / ac

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QUESTION: I live in Arizona in a 8oo sq ft park model.  I have to replace the heat/ac unit. (2 1/2 ton unit). I apparently have the option on the heat side of having heat strips or a heat pump.  Unit with heat pump is approximately $1,200 more than unit with heat strips.  What are the differences and what are the reasons to have heat pump instead of heat strips?

ANSWER: First 800 SF/2.5 Tons = 320 SF/Ton, way too much cooling. Buy a 2 ton or 1-1/2. The SF/Ton should be no less than 400 for a poorly constructed home with bad ductwork to more than 1,200 SF/Ton with today's energy codes and window technology.

If you're in a heating climate, a heat pump makes sense because the compressor is much more efficient than "heat strips". Keep in mind the air temperature from a heat pump drops as it gets cooler outside, will be cooler than body temperature below 35 or 40F. "Draft" complaints can develop.

With heat pumps, the more heat you need, the less you get. Below about 30F, the heat pump won't provide the required heating, so "supplemental" heat is used and then the fun begins: The heat pump can run 24/7 with discharge temperature widely fluctuating as the heat strip cycles on and off.

Also, heat pumps are less efficient at cooling than AC's.

Let me know if you need more.

Fred

---------- FOLLOW-UP ----------

QUESTION: Fred:

Thanks for the info. Your third paragraph is a little confusing. By the phrase "supplemental heat" I assume you mean some type of a room heater, correct?  Also the last sentence seems to imply that a unit purchased with a heat pump also has some type of heat strip. Will this heat strip then "kick on" when the outside temperature goes below the optimum operating temperature of the heat pump? Is there a way then to "turn off" the heat pump and leave the heat strip "on"? If this is the case, do I really need some type of "supplemental heating".  Also, your very last sentence is a little confusing.  I was under the impression that a unit I would buy would have a heat side and a cooling side. The cooling side is merely an a/c unit and the heat pump would have nothing to do with cooling.  Thanks again for your help.

Answer
A heat pump looks just like an AC on the outside. Inside, though, there are additional components that permit the AC to "run backwards" in the winter, removing heat from the outdoor air and adding it to the indoor air. It's much easier - more efficient - to heat the home using the compressor to move heat than using a strip heater to create heat.

As the air outside gets colder, there's less heat available so the strip heater is used to supplement the compressor. (IE: the strip heater is the supplemental heat). You only need the supplemental when/if outdoor temperature falls below about 30F.

The "EM HT" (emergency heat) switch on the thermostat deactivates the compressor and the strip heater then becomes the sole source of heat.

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Fred Weldin

Expertise

I can't help you if your whatsis won't work, people (Especially if it's a refrigerator); I have no experience with appliances, and I haven't been involved with H&AC service and repair since March 08, 1996 (Thank the Lord); I always send a "standard" reply to appliance questions and H&AC "Service and Repair" questions (about 20 a month), so if you want to know why your whatsis isn't working like it used to, ask someone else. A lot of my answers arenít read by the questioners; in that event, I always send reminders to read the answers for a month or more (the word "idiots" comes to mind - actually there's another more appropriate word, but discretion prevents its use here). If you have questions about how big a unit you need, if one room's warmer than the others, if you want an opinion oas to scope of work on bids received, etc. just ask. Do visit www.askweldin.com, there's a lot of good information on sizing, ductwork, efficiency, as well as some techniques accomplished DIY-ers can use to troubleshoot and improve their H&AC. Finally, I want to thank all of the kind, serious people whom I meet here: I enjoy working with you. My wife says I'm "snarky" from time to time; as for you others, please use your imagination as to the responses swirling on the snarky side of my brain when I read your questions.

Experience

53 years in the business. See www.askweldin.com

Organizations
ASHRAE, ICC.

Education/Credentials
B of ME U of D 1965, numerous classes, seminars and a lot of "Hands On" learning since.

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