Heat pump vs air conditioner (San Diego, CA)

yolo56February 17, 2013

Help. New to San Diego. We bought our home about 1 1/2 yrs. ago, without AC. Built in 2000., with 2 - 4 ton single stage Carrier furnaces. We were told not to worry, but it was unbearable last summer without AC.

We need 2 - 4 ton single stage AC units. In getting 4 bids, one company recommended a heat pump instead, and talked about the energy savings with SDG&E billing us at a baseline electrical rate, which would be less costly, the (single stage Trane XB130) HP more efficient & may be more desirable as it makes the home solar ready should we decide to sell. Another said it's not worth it because of all the extra work that needs to be done to set it up, HP can't be used with our furnace, and savings not worth it for our time frame. We were on a 3 - 5 year plan to stay in this home, but since we've been doing repairs, renovations, upgrades to home & garden it may be we would stay up to 10 yrs, but since we are putting so much into the home already, wants to go the route of the least amount of capital outlay needed, which would be the AC route. Mistake?

I can't find the information re "baseline'" electrical rates with HP at SDG&E. Are the single stage HP actually efficient, at 13 SEER? Variable and 2 stage with more SEER is better in everything. Would having a single stage HP be desirable at all, if someone would truly want to make the home energy efficient and upgrade to pv solar?

Novice to all of this, please share any experience or advice that would help us make a decision. Thanks.

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What efficiency is your furnace? What is your price for nat gas?

California's electric rates are really skewed especially from a provider that has tiered rates.

I personally think you should forget the HP idea and since you already have a Carrier furnace, then look at Carrier's Comfort 13 series with matching Carrier evap coil. Ductwork including return and insulation properties should be surveyed by dealer.

I have always been told that for California, nat gas furnace with AC was the mainstream HVAC combination.


    Bookmark   February 17, 2013 at 6:31PM
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How large is your house? Two 4 ton AC condensers is a lot of cooling. Has anyone done a load calculation?

    Bookmark   February 18, 2013 at 12:04PM
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I agree with Mike. Two furnaces with 4 ton drives, however oversized they may be, do not dictate two 4 ton air conditioners. A load calculation should be performed.

This post was edited by ryanhughes on Mon, Feb 18, 13 at 14:56

    Bookmark   February 18, 2013 at 2:17PM
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Thank you, to all, for your advice. The home is 3827 sq.ft. 2 levels, and we thought we needed to match the 4 ton furnaces. One company priced a 3 1/2 ton which I questioned, but he said if you need more they would upgrade it at no extra cost to us, so I guess they would do a load calc when we accept their bid or if we find it's not cooling enough.

Should we be request a load calculation from someone now? I don't remember anyone mentioning doing a load calculation during the bid process. I also find it's very chilly on the first floor, even when the thermostat is set at 70 - 72. I don't think this house is insulated very well and I guess all the heat rises as well. Advice on next steps to take?

Thank you for your help with this information. My husband is leaning towards AC, but I wondered if we were making a mistake not trying to go more energy efficient with a heat pump. It's all too new to me, but I'm learning.

    Bookmark   February 18, 2013 at 5:16PM
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"he said if you need more they would upgrade it at no extra cost to us"

That statement is a red flag for me. It tells me the contractor has not done a load calculation. I also question how a bigger unit can be provided at no extra cost.

You should be a load calculation as part of the quote. Most contractors don't want to or know how to do this.

The first floor may have duct issues. The contractor should inspect all the visible duct work for potential problems.

    Bookmark   February 18, 2013 at 6:19PM
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You do need a load calc for cooling on both zones.

I would like to know the model, size, and efficiency of both furnaces. Complete mdl number would be helpful.


    Bookmark   February 18, 2013 at 6:38PM
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Still believe a HP is a mistake.

Would be helpful to know more about your electric rate and nat gas rate. It is nat gas not propane?

Post back.


    Bookmark   February 18, 2013 at 7:08PM
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Wow! I don't know the furnace information, but I will start contacting all the companies that came to bid for that information. All were on Angie's List. I didn't know to ask for a load calculation, but will ask about that when I inquire about my existing furnaces.
We have 2 - single stage 4 ton Carrier furnaces on natural gas.
We have SDG&E - Energy Use Summary - week of 2/11/2013 came today
Gas Use: 65 Therms since 01/23/2013
Electric Use: 1006 kWh since 01/23/2013
Based Electric Use: Tier 4
Honestly, I don't understand it and will have to read up on what it all means, it's been a low priority till now.

I'm sorry to be so ignorant. Thank you everyone, so much, for the information & advice so far!

    Bookmark   February 19, 2013 at 12:08AM
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Two of the bids are for 2 - 4 Ton single stage ACs.
One bid for 2 - 3 1/2 Ton single stage ACs.
The fourth company just wrote down a ballpark price for various units, including the heat pump to consider and I've gone back to him asking for a firm proposal on the conventional single stage AC's. It's possible he would do a load calc to determine the AC unit size needed, I just don't remember. My husband got a bid when we first bought the home in 2011 and that proposal said 8 tons (I assume 4 tons each). Thanks for alerting me to the things I should be aware of.

    Bookmark   February 19, 2013 at 12:29AM
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One of the contractors, the "green" one, did mention the ducts were in good shape. And more than one said the furnaces are in good shape and have another 10 years on them. I did not mention to any of them how chilly I've been in the house, I didn't want to open a can of worms. The repairs & renovations we've endured already and what were about to do now, are wearing on me. I've been jumping around the various forums for advice! Thank you all again! Forums are new to me, as well.

    Bookmark   February 19, 2013 at 12:38AM
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4 tons of heating does not mean you need 4 tons of cooling. Usually they are different. Usually, I would expect SD to need more cooling than heating, but there are micro-climates depending on location. A load analysis must be done (ManualJ).

A 13 SEER HP is just as efficient as a 13 SEER AC unit. I would think where you are that electricity is more costly than gas, especially in the day time since you have time-of-day pricing on your power. Hence a HP would cost more to use than gas for heating.

The only reason I see to go HP would be if the power company gave you a discount and/or rebate. You might also check to see if they give something for higher than 13SEER. In your case, it would be good to look for higher SEER due to the power savings.

    Bookmark   February 19, 2013 at 6:35PM
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