No heat, getting cold, need help evaluating system recommendation

missstellaNovember 30, 2011

Okay, so our upstairs unit died and it is getting cold. Thankfully, we have a working unit downstairs so we can keep the majority of the living space warm for now, but I really need to make a decision about these systems.

The upstairs unit heats/cools approximately 1000 square feet of living space--3 bedrooms, 2 bathrooms. The home is located in Atlanta and is approximately 60 years old. Our current unit is 2.5 tons AC with gas furnace and has been adequate for our needs. The unit is in the attic. Insulation in the attic is R30 (I believe) and all windows are fairly new double-pane. We installed a Carrier duel fuel unit several years ago to replace our downstairs unit and have been happy with it so far--A 3 ton/80% AFUE unit heating/cooling approximately 1600 sq. feet over basement/crawl space.

I've had quotes from two companies and prices are similar (not great prices, but I think quality units and quality companies). Both companies have recommended new duct work.

The issue is this, one company has suggested that a 2 ton system will be adequate for us with a minor insulation upgrade and the other company is suggesting a 3 ton system. On the surface, both systems look alot alike, but the tonnage difference makes me wonder and I worry about being over or under served. This is a long term home for us and comfort is key. What's your opinion/recommendation?

Company 1 - Carrier system

Furnace 58CUA070 80% AFUE 70000 BTUs

Heat Pump 25 HWB624 16 SEER 2 tons

Coil C30H

Infinity controller

He recommended new duct work with some supply rework to alleviate hot spots and additional insulation.

Company 2 Rheem system

Furnace RGPE-07GAMKR 80% AFUE 70000 BTUs

Heat Pump RPQL-036JEC 16 SEER 36000BTU 3 tons

Coil RCFL-83617CC

Thermostate RHC-TST305UI

He recommended a damper system for the new duct work to alleviate hot/cold spots.

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you know the proper way is to have a manual j done to determine what size to go with. Other than that If your house is well sealed and insulated it's better to undersize a little depending on your humidity level. Ijn other words less humidity less tonnage for the summer time.

    Bookmark   December 1, 2011 at 8:40AM
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Thanks for the comments. We live in Atlanta. Humidity can be pretty high, and it gets hot in the summer, but we also experience some cold and wet winter weather. I have specifically asked for a system where I could adjust the humidity level to increase comfort. Our house is older (60 yrs.), but as we replace, improve, renovate we have upgraded sealing and insulation. We have put in new windows, replaced doors, etc. While a Manual J is good, isn't it possible that the calculations will change as we make improvements? If so, what are the major factors that would change those calculations?

I know that both companies took the appropriate measurements of the space, windows, returns, supplies and insulation as they currently exist. Although no one put any calculations in writing for me. We talked about our plans for the space which is not going to be expanded or significantly changed over the next 5 years. I have experience with both companies and have no reason to question them "selling" me something other than what they think I need.

I did find it curious that each came up with a different HP system size recommendation--the furnace piece looks like a wash, but given it is a duel fuel situation the HP is the piece I think I need to focus on--especially since it will run more frequently than the furnace given my location. I work from home and my office resides on the second floor so comfort is key in this space.

Any other thoughts?

    Bookmark   December 1, 2011 at 10:27AM
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It would seem a 2 ton heat pump would adequate for a 1000 square foot area in your part of the country. A heating and cooling calculation is the only way to be sure.

I think the model numbers for the Carrier equipment are wrong. I think the furnace should be model number 58CVA070. This the Infinity 80 70,000 BTU furnace. It's Carrier's best furnace in the 80% AFU class. I think the heat pump model is wrong. I can't figure out which model it should be. Also is the contractor specifying a Carrier coil? If not ask it be included. I also recommend you get the Infinity Controller.

I am not familiar with the Rheem equipment. I can't comment if it is equivalent in features.

    Bookmark   December 1, 2011 at 10:35AM
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Thanks for your comments. You are correct, I had the furnace numbers wrong. It should be 58CVA070. I looked up the Heat Pump numbers and it appears the the model should be 25HNB624 (the salesman's N looked like a W to me). Does the 24 at the end of the HP number indicate that this is a 24000 BTU system? The coil is listed as being Carrier, but I can't find it on their website with the number listed. Based on the correct model numbers of the HP and Furnace what would be recommended? The controller is the Infinity controller. The dealer is a very reputable dealer and an authorized Carrier dealer so I'm not worried they are trying to shortchange me on the coil, but I do want to make sure I get the best match for this system.

The Carrier dealer recommended new duct work, because our existing duct work is old and leaky but did not specifically talk about a damper system like the second dealer. How does a damper system work and is it something that can be added to an existing system as needed?

Also, when a new system is put in should refrigerant lines be replaced or flushed or is that a minor issue?

Thanks again.

    Bookmark   December 1, 2011 at 11:22AM
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The 25HBN624 is an Infinity 2-stage heat pump. I am sure it will perform very well as an AC. I am not the heat pump expert, so I advise you about its performance as a heat pump. I believe the Carrier heat pumps don't have demand defrost. I am not sure how important that is for the Atlanta area.

You need the coil model to find out if this is a correct match. The AHRI listing will give the performance numbers as a heat pump and AC.

As a general rule I would want the line set changed since you are changing refrigerants (R22 to R410A). However changing lines running up to an attic may be very difficult and expensive. In that case the lines can be flushed. You have to trust the contractor will do this correctly and the old lines are sized properly for the new unit. Ask the contractor about this.

The damper is used to create separate zones. I assume all of your duct work is exposed in the attic. I don't see why the duct work could not be fixed in order to remove your hot and cold spots and avoid the added expense and complexithy of zoning. Talk to the contractor about this and get his opinion.

    Bookmark   December 1, 2011 at 12:24PM
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A couple of comments.

What size and eff is current furnace?

I would say both the Carrier and Rheem furnaces are oversized.
I do know the Rheem two stg var speed RGPE is available in a smaller
size. I would want to see a load calc in writing.

The coil in the Carrier quote appears to be a non Carrier third party coil. I would not have it.

Whether you want a heat pump is up to you. You have to evaluate your

electric rates and the added cost. I certainly don't see how a 3 ton condenser in the Rheem quote is correct. I would stick with a high eff condenser either AC or HP in a 2-2 1/2 ton model

I would recommend a good box filter cabinet.

Rheem is quality HVAC often underrated and overlooked.

I would want to know about the damper upgrade the Rheem dealer is discussing. I suspect he is just talking about adding manual damper controls on the supply runs to each room.

Refrigerant lines must be sized correctly to the mfg specification. Flushing
and reusing existing refrigerant lineset is an acceptable practice as long as the size is correct. Can't be close. This is not horseshoes.

Rheem furnace quoted must have a two stg thermostat to work with best and full functionality. You do not want to use a timer from the control


    Bookmark   December 1, 2011 at 12:29PM
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Current furnace I think is 80000 BTUs--based on what was left behind by previous owner--it was installed in 1988. I don't know about efficiency level. I can't get to the info plate on the furnace because of its placement in the attic. I was thinking the 3 ton was overkill also since that is what is currently on my main level which is the same layout, but with 2 fairly large rooms extended off of the main house. I'm curious why you think 2 tons might also be oversized?

I just spoke to my Carrier provider regarding the coil and he was attempting to use a different coil ADP? so that we could qualify for tax credits, I told him we would prefer a matched Carrier coil--he gave me CNPVP30. (also, we don't qualify for the tax credits since we already took the max on our other system).

Refrigerant lines will be flushed as there is no access to replace, but sizing is not an issue according to dealer as our previous system was 2.5 ton.

Media Air Filter is included with both quotes.

I have been happy with the HP on our lower level and like the duel fuel option since we expect to live in this house for a long time. Gas prices fluctuate here and it's my understanding that electric prices are set to rise soon, so I'm hedging my bets and keeping my options open.

I was intrigued by the Rheem system, but not sure it makes sense at this point.

Can you tell what exactly is demand defrost (I don't think we need it here, but I'm curious). Also, what specific items would affect the load calculation?

Thanks again for your comments and expertise.

    Bookmark   December 1, 2011 at 2:32PM
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Heat pumps operate by moving heat from one place to another. In the summer, they move heat from outside to inside and the indoor coil gets cold with the outdoor coil getting hotter than the outside temperature.

In winter, it moves heat from outside to inside with the indoor coil getting hot and the outdoor coil getting cooler than the outdoor temperature. When the outdoor coil gets this cold, condensation can freeze on it blocking it up. Systems solve this by having what is called a 'defrost cycle'. Carrier uses a system with a timer which activates the defrost cycle whether you need it or not. Others, like Trane (I think) use a 'demand defrost' system which activates the defrost cycle based on perceived load.

The defrost system uses more power, hence a 'demand defrost' system is more efficient in that it only activates when necessary.

You mentioned something about dealing with hotspots upstairs. Were these hotspots in the summer or winter?

On your old system, did the AC run continuously on hot days or did it cycle on/off? If it ran continously with the temp set at 78f then a slightly larger unit might not be bad. But if it cycled, then going larger would be a bad idea.

    Bookmark   December 1, 2011 at 4:26PM
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To your last question.

Without going into technical jargon, electronic demand defrost is a feature on heat pumps that eliminate unnecessary, nuisance, and costly defrost calls. It is found only on a few brand/models of heat pumps including Trane/AmStd, York, and Rudd/Rheem. It is much more desirable over the cheap time/temp method of defrost.

I don't think I said 2 ton was oversized. since this is upstairs system, I would probably stick to a 2 1/2 ton assuming you have has no cooling and/or humidity issues.

Here is the Rheem system I would consider.

3879236 Active Systems RHEEM RPQL SERIES RHEEM MANUFACTURING COMPANY RPQL-030JEZ � RCFL-H*3617 RGPE-05?BMK? 29800 12.50 15.00 29200 9.00 18400

Existing lineset size will need to be verified. You would need a good two stg thermostat suitable for DF operation along with outdoor sensor.

The heat pump would offer about 29 KBTUs and the two stg furnace would have a low stg of 35 KBTUs and high stage of 40 KBTUs which should be more than adequate for 1000 sq ft upstairs living space.


    Bookmark   December 1, 2011 at 4:28PM
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Thanks for the explanation.

The hotspots are during the summer, as we have several South/West facing windows with minimal window coverings that allow in a lot of heat. In the winter we have an area that gets cold on the opposite side. I think the solution is to re-work and adequately seal the duct work and to evaluate the placement of supplies and returns in the room that gets the temperature fluctuation.

For the most part, the upper floor is comfortable and we don't find ourselves changing clothes as we change floors. Our old system did not run constantly or cycle on and off a lot until the end...

    Bookmark   December 1, 2011 at 4:44PM
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tigerdunes--we crossposted. I'm sorry I mis-read your original post--you were specifically referring to the furnace with your comment, not the HP.

I'll review your recommendation on the Rheem system, thanks.

If I went with the Carrier system, which furnace would you recommend with the HP listed?

I am currently leaning toward the Carrier since the company is one who has done maintenance for me for a number of years and we have a solid history. It doesn't hurt that they are currently running a customer loyalty program that will save me close to $700.00 on top of power company and manufacturer rebates right now. I have to at least consider this in the mix.

Thanks again for comments.

    Bookmark   December 1, 2011 at 5:35PM
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The Carrier Infinity furnace you have posted is very nice. It would match nicely with the Infinty heat pump.

A 70,000 BTU furnace may be a little oversized. Assuming your duct work can handle the air flow, the only other concern with be short cycling. I don't think you would experience much of this. I assume you will lock out the furnace at temperatures above 30 degrees, so the furnace will only operate at low temperatures. In addition the furnace will use the low stage which will lenghthen the time the furnace is in operation.

    Bookmark   December 1, 2011 at 7:47PM
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Could I pair a less robust furnace with the HP listed above? If so, what?

I would probably lock out the furnace at around 35-40 degrees as that is what is suggested for our area and I really like gas heat better, but wanted the option to use electric if gas prices move up like they have in the past. We will be putting new duct work so it should be designed to handle whatever is being put out.

    Bookmark   December 1, 2011 at 8:53PM
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Just wanted to be clear about this point.

For me it is all about quality and correct siziing.

I recommended the Rheem because their RGPE mdl furnace has a smaller size that I feel is a better choice than The Carrier. I would ask Carrier dealer what are your options on a two stg var speed 80% eff furnace that is smaller that the Infinity 80 they quoted. Not certain there is one. Oversizing s never good and only costs you more to operate each month sometimes with less comfort due to short cycling.

With new ductwork, you want R8 insulation both trunk lines, supply, and returns.


    Bookmark   December 2, 2011 at 8:57AM
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I did a quick look at the AHRI directory. It looks like your choices are very limited with the Infinity heat pump paired with a 80% AFUE furnace. There may be a discountinued furnace which would be an approved match, but you may have trouble finding it.

You could move to the Performance heat pump. Some models come with 2 stages. You should be able to save some money and not give up much in features and efficiency.

    Bookmark   December 2, 2011 at 8:58AM
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You are making this very complicated chances are you won't be satisfied with anything.

    Bookmark   December 2, 2011 at 10:00AM
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The fact that your old unit was cycling 'normally' would lead me to say that you do not need to go up in size. Rather, you have some duct issues where you need more cooling in one place during the summer and a bit more heating in another place in the winter.

    Bookmark   December 2, 2011 at 4:10PM
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Just a suggestion. Be careful about oversizing the AC, because it will reduce your comfort.

    Bookmark   December 2, 2011 at 5:50PM
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