Is my HVAC guy snowing me?

[Kent in KC]

I'm building a new home in Kansas City, and don't think I'm getting a good A/C recommendation. Before I go out and get a couple more bids, I thought I'd see if any of you fellows could give me some advice regarding the size of the unit I would need.
Now, I know there is the Bubba method and the correct method for sizing a unit and the correct method involves a lot of inputs and calculations.

So, here is the basic sketch: it is a ranch with full finished basement, 3500 sq ft, 4BR, 3.5 bath, south-southeast orientation, Andersen low-E casement windows, (83 sq ft of windows on the south, 5 sq ft of window on the west, 55 sq ft of windows on the north and no glass on the east). The walls are 6", insulated with Icynene foam, all exterior doors are good fiberglass TemperTru (?). The living room has a vaulted ceiling up to 14' and two 2x2 Velux skylights. The roof has 24" overhangs and the underside of the roof is insulated (with Icynene) instead of the attic, so we're keeping the heat out of the attic. Entry to the house is through a closed foyer, garage or back porch that all act as airlocks to prevent rapid loss of cooled air.

I had them install the A/C outlets in the ceiling instead of the floor for more effective destratification.

The house is only shaded along the west side in late afternoon and sits atop a breezy hill. My wife is a teacher so during the summer 'vacation' the home will need to be kept comfortable during the hot part of the day (no thermostat setback).

Based on all that, does a 3.5 ton, 13 SEER central air unit sound right? Sounds big to me and I do not want an oversized unit.

BTW, before you recommend a heat pump, it ain't in the budget. I blew too much on solar heat and radiant floors!

Any advice would be appreciated. Thanks, guys.

 

[Junkman]

I would recommend that you get a few more estimates for size and price. Too late to do it now, but had you asked this question before you insulated, I would have suggested that you have the ductwork sprayed also. A friend of mine did the, and it quieted the system immeasurably by comparison to the system operating prior to the home being insulated. They were building in the winter, and the heat was the first thing to be completed and turned on for the workers after the electric.
I trusted one HVAC contractor to give me advise when I built my home, only to find that the system was undersized for the house. After fighting with them for 6 years because the system wouldn't cool the home on very hot days, I finally had the manufacturer come to check it out. They said it was undersized and the installing dealer replaced it for free rather than fight me in court. If they think that the $$$ are going to effect them getting the job, then they will low ball the job and do a sub standard install to get the work. This wasn't the case with my job, because I paid a healthy amount for the job, but he dealer just scrimped on the job to make extra profit. Now, I always get 2 or 3 prices on any job first and make sure that I get the specs in writing along with the price. If I find discrepancies on the specs, then I get additional quotes and question the specs. You only want to do this job once and pay for it once.

 

[BoCRon]

Go check out www.hvac-talk.com. A forum all about hvac, whooda thunk?
Annette

 

[chaingang]

I'm building a new home in Kansas City, and don't think I'm getting a good A/C recommendation. Before I go out and get a couple more bids, I thought I'd see if any of you fellows could give me some advice regarding the size of the unit I would need.
Now, I know there is the Bubba method and the correct method for sizing a unit and the correct method involves a lot of inputs and calculations.

So, here is the basic sketch: it is a ranch with full finished basement, 3500 sq ft, 4BR, 3.5 bath, south-southeast orientation, Andersen low-E casement windows, (83 sq ft of windows on the south, 5 sq ft of window on the west, 55 sq ft of windows on the north and no glass on the east). The walls are 6", insulated with Icynene foam, all exterior doors are good fiberglass TemperTru (?). The living room has a vaulted ceiling up to 14' and two 2x2 Velux skylights. The roof has 24" overhangs and the underside of the roof is insulated (with Icynene) instead of the attic, so we're keeping the heat out of the attic. Entry to the house is through a closed foyer, garage or back porch that all act as airlocks to prevent rapid loss of cooled air.

I had them install the A/C outlets in the ceiling instead of the floor for more effective destratification.

The house is only shaded along the west side in late afternoon and sits atop a breezy hill. My wife is a teacher so during the summer 'vacation' the home will need to be kept comfortable during the hot part of the day (no thermostat setback).

Based on all that, does a 3.5 ton, 13 SEER central air unit sound right? Sounds big to me and I do not want an oversized unit.

BTW, before you recommend a heat pump, it ain't in the budget. I blew too much on solar heat and radiant floors!

Any advice would be appreciated. Thanks, guys.

A good rule of thumb is 500 square foot per ton. I have heard with foam insulation you can use less tonnage but don't know how much. I would strongly recomend doing two system, one for the basement and the other for upstairs. It is very hard to get one system to work effectively. To make it work moderately well, you need to set up zones(gets complicated and pricey) I have about 1900sqft on the main level of my ranch style with a 1300sqft daylight basement finished(built into the hillside). I have a 2.5 ton downstairs and 4 ton upstairs and it works great. My heating contractor would not do a single unit because he said they get to many complaints about hot and cold rooms. House is 4 years old R39 in the ceilings R19 in walls, Andersen low E double hung windows, 11SEER heatpumps and located in central GA. Paid 8K when I built the house. Have been very pleased with being able to keep the different levels comfortable.

 

[04 Navi]

I'm building a new home in Kansas City, and don't think I'm getting a good A/C recommendation. Before I go out and get a couple more bids, I thought I'd see if any of you fellows could give me some advice regarding the size of the unit I would need.
Now, I know there is the Bubba method and the correct method for sizing a unit and the correct method involves a lot of inputs and calculations.

So, here is the basic sketch: it is a ranch with full finished basement, 3500 sq ft, 4BR, 3.5 bath, south-southeast orientation, Andersen low-E casement windows, (83 sq ft of windows on the south, 5 sq ft of window on the west, 55 sq ft of windows on the north and no glass on the east). The walls are 6", insulated with Icynene foam, all exterior doors are good fiberglass TemperTru (?). The living room has a vaulted ceiling up to 14' and two 2x2 Velux skylights. The roof has 24" overhangs and the underside of the roof is insulated (with Icynene) instead of the attic, so we're keeping the heat out of the attic. Entry to the house is through a closed foyer, garage or back porch that all act as airlocks to prevent rapid loss of cooled air.

I had them install the A/C outlets in the ceiling instead of the floor for more effective destratification.

The house is only shaded along the west side in late afternoon and sits atop a breezy hill. My wife is a teacher so during the summer 'vacation' the home will need to be kept comfortable during the hot part of the day (no thermostat setback).

Based on all that, does a 3.5 ton, 13 SEER central air unit sound right? Sounds big to me and I do not want an oversized unit.

BTW, before you recommend a heat pump, it ain't in the budget. I blew too much on solar heat and radiant floors!

Any advice would be appreciated. Thanks, guys.

Sounds about right, maybe even on the small side. Our last house 2400sq ft up and 1200sq ft down , we had a four ton 10 seer and it nothing to spare on a hot 85 degree day. This was also located in the Pacific Northwest I might add.

Current house is 3500 down and 750 up and we have two systems for a total of six tons. Mind you the house has a bunch of 12ft ceilings and no shade. We were building during the summer so I can't say how it will be for living.

 

[carguy123]

I am in the same boat as you. I have gotten 12 different bids from AC guys and have 12 different suggestions with no/very few commonalities of bid. I have talked to Trane and Carrier direct and gotten a good load calculator (from their sites) and calc'd my required AC to 8.5-9 tons. Due to the way the units you buy are sized I will be happy with 10 tons. I have very similar insulation and window ratios and none of the AC guys wanted to take that into consideration cause "you'd be unhappy with me if it didn't cool right". I think it's just that they are all idiots.

What are you using for heat? I have natural gas which is quite a bit cheaper than a heat pump. If you have to buy propane then a heat pump might be a better idea since the cost of propane can vary wildly.

You can Zone the units which give you controls on the different floors for more comfort.

 

[fefarms]

If the basement is fully below grade (not daylighted) then it has a nearly negligible heat and cooling load. So your house may be only 1750 square feet, which makes the 3.5 ton unit possibly a bit on the large side. You don't need two units if half your square footage is a basement.

Just for the sake of comparison, I heat and cool 5800 square feet with ONE 4 ton heat pump, without zoning. This house has a 2000 sq foot basement, 2000 sq foot first floor, and an 1800 square foot second floor. This is in the Pacific Northwest, it is a two-stage ground source heat pump, and I spent a LOT of effort designing the ductwork and keeping it all within the conditioned space. The electricity to heat or cool the house runs about $60 in the coldest/warmest months.

 

[HoosierBuddy]

"you'd be unhappy with me if it didn't cool right". .

I think that's the issue. If they undersize the unit and it won't cool, they're going to be on the hook to come back and replace the unit. If they oversize it...at least it's going to work.

I don't know anything about 2-stage cooling, but that SOUNDS like the berries to me. I have a 2-stage furnace that ALMOST never gets off the low setting (70,000 BTU)...but when you need the honking heat, it'll jump up to 100,000 for as long as you need it to. Great concept. It makes the load sizing less critical, and it's QUIET at low as the DC variable speed fan slows down.

My boiler in the garage does the same thing. It modulates from 20,000 to 150,000 BTU's depending upon the load requried by the 3 zones it serves. If they've got a/c units that do the same thing, that sounds like a winner to me.

Regarding the HVAC forums and asking for advice? Don't bother. They don't give advice to homeowners over there. They berate you for daring to ask "professionals" questions. Do as search under my user name, and you'll see what I mean. What a bunch of pricks.

It's a shame too, because every other forum I'm aware of loves to answer questions about their topic of interest to anyone that asks. If they even SUSPECT you are going to THINK about doing something yourself over there they go Ape Do-Do.

Phil

 

[mike944]

You definitely don't want to over-size it. You'll end up with cold but damp.

 

[Kent in KC]

Danski, thanks but I have no can lights, stainless or granite in my home. I'm putting my money in energy efficient hvac, appliances, etc.

Phil, thanks for the insight about the hvac forums. One of my favorite boards by the way, is yesterdaystractor.com. A bunch of smart people, friendly and willing to share whatever expertise they have on any subject, tractors or otherwise.

 

[HoosierBuddy]

There is a huge difference between hacking in a HVAC system and installing it properly. Both may heat or cool, but only one way will deliver the efficiency and comfort you are paying for.

That's why I do my own HVAC work. Why let some over-booked, over-wrought, over-priced, contractor sell me the same unit he's installed in the last 6 jobs he did, then send his under-paid, over-worked, under-aged, over-medicated, crew out to put it in half-assed, when I can put the ONE GUY on the planet that really CARES if the job is done right on the job.

Me.

I'll have to start researching those multi speed systems. Those would likely match up well with the furnace I installed at my home.

Phil

p.s. I'm just b.s.ing you. Good HVAC guys are hard to find. If you get one, you better hang on to him. Mine died about 10 years ago, and I still miss him.

 

[MyDomain]

You will not get a better answer on HVAC-TALK unless you are a pro...even then you would get chastised for not knowing. I should know...I'm a pro member there.

You should definately get another pro to look at it; if not two. They will need to measure all rooms and windows, note your insulation values, note orientation of the home, etc. A proper calculation is your only answer.

 

[Kent in KC]

Update: The electric coop did the heating and cooling loading study for me (free). It used a computer program, was quite detailed and considered many things I had not thought of. They came up with a 2.65 ton A/C requirement, about 30% less then the A/C guy wanted to sell me.

 

[Kent in KC]

Update: The Electric coop did a study for me and ran it all trhough a computer program. Result: I need only 2.65 tons of A/C for my 3500 sq ft house. Big reasons: Icynene foam insulation, south-southeast orientation (passive solar) with 24" overhangs over the windows (to shade them in summer, low-E windows.

BTW guys, you really don't need to air condition the basement, the cool air settles there and it is naturally cool anyway. I have one A/C outlet in the basement and fresh air vents (and ceiling fans) in each BR.

We are doing other interesting things like the earth cooling tubes (drawing air through six 150' 4-inch PVC tubes buried 5 ft underground) for filtered fresh air at about 55-65 degrees year round. I doubt if the A/C will be used much.

 

[Innovate1]

Sounds a bit low to me. You sometimes have to pay for a real HVAC load calculation. If the utility will do it that's a big plus. Two speed systems are great in that they aren't as critical on sizing as others have noted. A lot depends on attention to detail on insulation and air sealing. A basement is still some load - think about the top of the foundation wall and the rim joist - both directly exposed to outside and inside air. We had the basement insulated when we did our house. I saw that they insulated the walls but not the rim joist so called them on it. They said if you would have paid for basement insulation we would have done that. I said I did pay - look at the basement walls are insulated. They said oops, our mistake, we will fix that. Seems odd that the workmen AND the supervisor both made the mistake. And overall the company was good. They did a great job air sealing all the wires into the attic and other things.

 

[Jim greengo]

Is the sq footage including basement also?
I normally dont figure the basement into the sq footage for sizing ac.
I normally figure about 600 sq ft of above ground area per ton.

 

[u3b3rg33k]

I'm building a new home in Kansas City, and don't think I'm getting a good A/C recommendation. Before I go out and get a couple more bids, I thought I'd see if any of you fellows could give me some advice regarding the size of the unit I would need.
Now, I know there is the Bubba method and the correct method for sizing a unit and the correct method involves a lot of inputs and calculations.

So, here is the basic sketch: it is a ranch with full finished basement, 3500 sq ft, 4BR, 3.5 bath, south-southeast orientation, Andersen low-E casement windows, (83 sq ft of windows on the south, 5 sq ft of window on the west, 55 sq ft of windows on the north and no glass on the east). The walls are 6", insulated with Icynene foam, all exterior doors are good fiberglass TemperTru (?). The living room has a vaulted ceiling up to 14' and two 2x2 Velux skylights. The roof has 24" overhangs and the underside of the roof is insulated (with Icynene) instead of the attic, so we're keeping the heat out of the attic. Entry to the house is through a closed foyer, garage or back porch that all act as airlocks to prevent rapid loss of cooled air.

I had them install the A/C outlets in the ceiling instead of the floor for more effective destratification.

The house is only shaded along the west side in late afternoon and sits atop a breezy hill. My wife is a teacher so during the summer 'vacation' the home will need to be kept comfortable during the hot part of the day (no thermostat setback).

Based on all that, does a 3.5 ton, 13 SEER central air unit sound right? Sounds big to me and I do not want an oversized unit.

BTW, before you recommend a heat pump, it ain't in the budget. I blew too much on solar heat and radiant floors!

Any advice would be appreciated. Thanks, guys.

shoot, a heat pump should add like $200 to the quote. reversing valves are pretty cheap.

 

[Snapped-off]

OP has been gone since March of '07 boys...

 

[yeldogt]

This is a very very old thread -- from 2007. Hope he built the house as the crash was about to start.

Traditional split HVAC was in the early 2 stage back then .... I had done a Carrier 2 speed just a couple years prior and that was cutting edge. Trane was making two speed with twin compressors in the top model. Mini splits were inverter by that time but only a few were hyper heat.

Getting a proper load done is so important and sad to say still not being done all these years later. When building new some states are mandating insulation code inspection ... but, in the states I live they don't have to combine with load calculations. Blower door tests get done for energy audits years after a house is built .... the best time to have one is after the insulation goes up and before the drywall.

I will also add that getting a load done when using spray foam is an additional problem as it seems the programs just don't capture everything ..... My last couple projects have been done by a guy in another state who checked all the numbers for me off of rather detailed plans. W/ foam in the mid-atlantic the numbers are always over 1k SF Per Ton of AC ... my last was almost 4kSF with 36k of cooling.

Humidity is a big driver of comfort. That's the great thing about the multi speed equipment .. ability to control the humidity w/o over cooling. We have a house in PA that we mostly use in the winter. It has a multi speed heat pump that I keep on 78 when not there and set the humidity to 52% (most of the time). When we get there 78 is actually quite comfortable w/ low humidity. The system has the traditional Home/ Away setting and the home brings the temp to 75. With low humidity bringing the temp down is quick.

 

[fitter30]

What are doing for heating? Coop use a manual j for their load calculation? 3500 sq. ft. house not separating the bedrooms from the rest of the house is a mistake. Having two loads will have instead of one will be easier to control and energy efficient. The contractor is more important than the brand of equipment. Ceiling diffusers for stratification? There are ceiling fans that do a better job. Need to sit down hvac mechanical engineer that designs homes.

 

[welder4956]

Deleted - old thread.

 

[welder4956]

OP has been gone since March of '07 boys...

LOL - I should look at the dates more often when somebody replies to an old thread.