HVAC Guys - Need Some Advice Please

[Ranman]

I'm trying to get an idea of what size AC unit to install in my house. My HVAC guy is offering either a 4 ton and 5 ton unit by Comfortmaker (10 SEER leftovers). Without getting into a complex cooling load calculation, can someone offer an opinion based on the information provided below? Thanks for the replys.

House built in 2005
3000-3100 sqft Colonial
All 4 bedrooms are upstairs
Fiberglass roll insulation in all exterior walls and a single layer in ceiling
Philips Marquee Contractor grade windows
Avg U-value is .49
Avg Solar Heat Gain is .62
All windows face North (Rront) or south (Rear)
Single Carrier 80% furnace in basement with 5-ton blower
Dark exterior brick and siding with black shingles

[Greg K]

I'm assuming you're only talking about the condensing unit and coil to be matched with the furnace in the basement and the upper and lower levels are not zoned.

Plain and simple...go with the 5 ton unit.

[tamburello]

Hi Randy, I just started working for the biggest HVAC distributor in the state a few months ago. I'm just getting a handle on all the products we sell and I am far from knowing enough to recommend sizing on new installations.

However, I do know that it would be worthwhile to look into getting a heat pump instead of the typical condenser. A heat pump is basically a condenser with a reversing valve. It will heat your home in milder weather above 35 degrees or so and your furnace takes over when the temp drops below the level that the heat pump can effectively heat your home. With todays prices of natural gas and electricity the payback is fairly short on the extra $300 or $400 you'll pay for a heat pump over the standard condenser. Heat pumps are installed much less frequently than standard condensers so finding a 10 SEER heat pump might be a trick.

- Jeff

[Greg K]

Then again..as suggested...go dual fuel...use the heat pump in milder weather and with an outdoor air sensor it'll lockout the condensing unit and switch over to gas for heat below a certain temp. Still 5 tons though.

[TuxedoPk]

Randy- 18 months ago I had (2) 5 ton and (1) 3 ton 13 Seer Carrier systems installed that provide both cooling and heating (via heating coils attached to the blowers).

If budget isn't extremely tight and you're planning on staying in the home a few years I'd really look at the Infinity System from Carrier; I believe it is still considered top of the line. Aside from the greater efficiency from the 13 Seer, the contol system is terrific and can interface also control humidity.

I think you will find that a 5 ton system will best meet your needs, but I'd be hesitant to hire an HVAC company to design your system that doesn't do the full calculation.

http://www.residential.carrier.com/systems/infinity.shtml

[half shell]

3100sq ft two floors one or two zones? If two zones it must be with dampers and I would have some concerns about air flow over the coil you could have an icing problem when only one zone calls.

Amust have is an attic ventilator to cool the attic as much as possible to help the bedroom area on second floor cooldown.

If house is on one zone keep the attic ventilator and add a thermostat to the second floor for cooling only and lock out the t stat on the first floor during summer months.Also turn down dampers or grillwork on first floor and keep second floor wide open during summer months.

I have just purchased a home with the same set up only a little smaller and am looking to do the same thing.

House was built in the 40's and I am about to start a full renovation while I live in my current home.

I am a plb/hvac contractor feel free to ask any further questions.

Regards Bob

[half shell]

PS to answer your first question 5T.

Regards Bob

[Ranman]

One furnace one zone. For the 3 main coolng months 13 SEER does not appear to be worth the money $500-$600 and only saves ~$15/mo (12 years to reach break even).

Can you elaborate on the attic ventilator? Electric? Automatic? How much $$??

I may have to figure out how to manage the T-stat situation. I have a Honeywell VisionPro tat can accept multiple remote temp sensors so there may be some versatility there.


I do plan to adjust the 1st floor dampers in the summer

I'm a bit surprised in that my HVAC guy is only recommending a 4 ton system. (this person is a family friend and the pricing is verrry competitive). He did my last house, my parents house, my fathers business and all have been fine. His basis for the 4 ton over the 5 ton is that too big a unit may not adequatly remove moisture and could potentially contribute to and/or facilitate mold issues. He said that the new homes with improved windows, insulation and the fact that I have no windows facing east or west should allow us to go down 1 step. Any thoughts on this?

I have a call into my guy to inquire on the heat pump setup. I don't know of anyone around here who has one, but the concept is clearly interesting.

[TuxedoPk]

I'm a bit surprised in that my HVAC guy is only recommending a 4 ton system. ... His basis for the 4 ton over the 5 ton is that too big a unit may not adequatly remove moisture and could potentially contribute to and/or facilitate mold issues. He said that the new homes with improved windows, insulation and the fact that I have no windows facing east or west should allow us to go down 1 step.
Any thoughts on this?


If I remember correctly, I used a variable speed blower with my Carriers to allow for better moisture control. Your HVAC guy is correct in that bigger isn't better- install the system that is sized appropriately for your use. I was wrong- the system was 17 Seer.

Does Michigan offer you any $ incentives to install more energy efficient systems?

[KRAVEN]

Randy,Don,t go with the heat pump not well suited for are area.Upstairs will be hard to cool ,what about a airhandler with seperate condensor located on second floor? You mat want to ask your contractor about this option.Without zoning you will not be happy with only 1 blower to distribute a/c in home.Make sure ducting is of adequate size for blower tonnage.

[half shell]

I agree on not over sizing however basic sizing in my climate would be approx. 500 sq ft per ton ie 2500 sq = 5t you are at 3000 sq ft so a little under is ok.

However since you will close the first floor dampers 4t for 2nd flr with some going to 1st floor will most likely be ok.

Go with the local knowledge on this one.

Forget the 13seer you will most likely throw the unit out before it has paid for itself.

Forget the heat pump too.

My current home dads home and my sisters home all have 10 seer and no e bill complaints.

Attic ventilators 100 or so to purchase plus install with built in t stat.

Do not run with out it you will not be happy with the cooling without it.

Regards Bob

[half shell]

Kraven that scorpion avatar is too cool!!!!!

Regards Bob

[motorcity]

Get a interupted service electric meter installed for the A/C system. Detriot Edison rarely shuts off the power on these and most times it is in the middle of the day at peak use, when most people are not home. This saves alot of money on your electric bill for the A/C. Well worth the cost.