[Scott F.]

The VRV/VRF condensing units are incompatible with a conventional furnace. The system is basically a heat pump that utilizes numerous cassettes or fan coils to distribute the conditioned air.

You need to go with a standard condensing unit that will mate to your existing furnace and coil.

[drphoto]

well, I was told I need 5 ton, and old was 4 (it didn't work very well, so maybe reason) and existing furnace blower couldn't handle. So I'd need whole new setup. If so, should I look at what you describe? Was quoted stunning price too ($10K)

[JLM]

It's really hard to give specific advice without inspecting your house.  We can't know all the variables that could rule out one solution versus another.  But you could ask local contractors about alternatives, including what's been mentioned.  Keep looking if they dismiss other options out of hand.  Many residential furnace guys also do commercial work so they should be well versed to other technologies.

In general dehumidifiers plus fans = air conditioning, so energy savings would be minimal.  If you open the house daily, it'd be worse than keeping the house closed with central air. 

[drphoto]

Yeah, I need to get some pro's in here. But thanks again for giving me something to consider.

[Scott F.]

$10k for a system isn't too far off for a residential contractor. Be sure the contractor you use is well versed in the local rebates from your utilities as there will be some available. The rebate won't be huge but it may pay for the next higher efficiency model up the line. And don't be afraid of an air to air heat pump. They can be incredibly efficient and are extremely reliable. That is the basis of the VRV/VRF design.

[drphoto]

The worst part of all this is homeowners wouldn't cover the loss. I'm inclined to go up on roof and pull out half the nails so next storm takes it off and let them pick up the tab. But then, they'd probably say it was too old. And cover next to nothing. I pay $2400/yr, premium, which I think is a lot, but dunno. Maybe that's average too if you say $10K not way high.

And no other insurance carriers will touch this place until I do some remodel/repairs.

[ctviggen]

The worst part of all this is homeowners wouldn't cover the loss. I'm inclined to go up on roof and pull out half the nails so next storm takes it off and let them pick up the tab. But then, they'd probably say it was too old. And cover next to nothing. I pay $2400/yr, premium, which I think is a lot, but dunno. Maybe that's average too if you say $10K not way high.

And no other insurance carriers will touch this place until I do some remodel/repairs.

We pay about $2,000/year for our insurance.  It behooves you (everyone) to change insurance every few years.  We did that this year and ended up paying less for more coverage.  Unfortunately, it's very time consuming.  My wife spent hours on the phone talking to multiple companies. 

For our AC units, I doubt anyone would steal them.  They're 20+ years old and use a different refrigerant.  (Although maybe that would make them more valuable?)  When we replace them, we're thinking of going to heat pumps and using our oil as backup heat.  It's just going to be expensive, because we'll probably have to replace basically the entire system, air handler, AC unit, lines, etc.  And if you're doing that, you might as well replace some/most/all of the ducting. 

[Atlplasma]

To the OP, whatever you do have a competent person calculate a Manual J (cooling) and/or a Manual D (heating) on your home before buying a system. A competent person is usually somebody like a RESNET rater or a HVAC engineer. (I used Optimal Building Solutions.) Do not trust whatever numbers the heating and air contractor may provide. Most don''t take the time to do a proper analysis, which means the systems they install are typically vastly oversized. If anything, you want a system that's a bit undersized (at least for cooling).

Split minis can provide heating and cooling without the need for ducts. (Ducts outside a conditioned space are a bad idea in any case.) Daikin is a premium brand, but there are many other manufacturers that are more affordable. With this type of system -- or any system, really -- proper design and installation is critical.

[drphoto]

thanks for advice. love this site!!

[Scott F.]

<snip> ....which means the systems they install are typically vastly oversized. If anything, you want a system that's a bit undersized (at least for cooling).

That statement may have some truth if you are buying the base model, single speed furnace and condensing unit but it isn't necessarily true for the top of the line, variable speed blower/compressor/condenser fan units. You have to really know what you are looking at when you pick manufacturers otherwise, the unit will not only not cool at peak load, it won't dehumidify either.

Every unit has a sweet spot in operational efficiency. Operating at their least efficient position on the operating curve is as full load, without exception, period. Undersized is not where you want to be. Think about it, you can equate it to your car. You could run balls out at living at the 7000 RPM red line much of the time. What happens? The motor wears out prematurely. Now flip that and keep the revs between 2500 and 3500 and you now get killer gas mileage and the car lives to see 300,000 miles. An air conditioning compressor lives under those same laws of physics.

A proficient HVAC designer looking to provide the highest efficiency at the highest number of operating hours may come up with a design that has the unit slightly oversized at peak loads but when operating for the other 70% of the time, the unit is at the sweet spot (for efficiency) on the curve. At these slower speeds, these units actually dehumidify better than at full speed. You have a better chance to wring the moisture out of the air when the air flows slower across the coil.

All of that comes with a cost. High Efficiency units cost more money. They have bigger condensing coils, more complex controls, more expensive motors and compressors, more technology. All that equates to more money. If you have a competent HVAC shop looking at your system (read=not the cheapest installer), they will run the calcs and show you how quickly the high efficiency unit will pay off the cost difference.

That typed, money always plays a factor in everyone's decision making process. I'm typically on the other end of the spectrum than most. I use, 'do it once, do it right, never regret' because ultimately, it was the right decision even thought it cost more money.

...if you haven't figured it out yet, I'm a mechanical engineer that specializes in energy retrofits for large commercial buildings.

[drphoto]

Thanks Scott. I'm also a do it once, not spec the cheapest sort. Hell I'll buy a Milwaukee power saw and use it once or twice a year. But just can't get junk, ya know.

BTW: I respect the hell out of engineers. I thought about ChemE, but my math chops are weak. Ok, I hacked though 3 semesters of calculus, but never hung on for DE or more advanced stuff.

I'll also have a ton of respect for skilled crafts people like electricians, plumbers etc. Seems like many look down their nose at people who use their hands and get dirty or don't have a BS. But those people have skills.

Hope that doesn't sound like a political message.

They're doing a major road project here....new OH river bridge. I'm amazed at the brainpower it takes to design that, and the logistics to implement while keeping traffic flowing at least semi normal. And then there's the dudes that have to go out when it's -5 and install rebar, or pave when it's 90. Impressive stuff.

[drphoto]

Wow, the net is scary. I just got a pop up ad for HVAC estimates. I guess based on our conversation here. creepy.

[Atlplasma]

I'm comfortable with Scott's answer and no doubt his mechanical engineering background makes him the more knowledgeable person to advise you. Ideally you want a system that is optimal for your heating and cooling loads. My house is very energy efficient (1.1 ACH/50), so we are able to condition 3,200 square feet with just two tons across three zones. Our system is a bit undersized for peak loads (Think a 95 degree day when the heat-pump clothes drier on the second floor is in use.). The system can keep the second floor at 78 degrees, but just barely. The solution here is to convince other parties to wash and dry clothes in the evening 

My air-source heat pump is 16 SEER and has a two-stage fan. (Update. Actually it is a 17 SEER.) I would have liked a a higher SEER and better components, but the mechanical engineer who evaluated our house advised against spending any more since we would never recoup the cost over the projected lifetime of a name brand system.

I'm planning a new house that will be smaller (1,500 square feet) and more energy efficient (.6 ACH/50, that is performing to the Passive House standard). I think we will be able to heat and cool it with a single fairly small split mini system since the loads will be low. I really like the Daikin systems, but it may make more economic sense to go with Mitsubishi.

One FWI to anyone contemplating a tight house. Ventilation is just as important as heating and cooling. Most homes have pretty lousy indoor air quality.

[ctviggen]

Wow, the net is scary. I just got a pop up ad for HVAC estimates. I guess based on our conversation here. creepy.

They're absolutely tracking you.  I clear my cookies when I can remember to.  If you want to see how well they're tracking you, go to Amazon, search for something, click on it.  Close the Amazon window.  Go somewhere else.  See what ads pop up.  The same can be said for any website. 

For us, we're having a "green" builder come in to add insulation in the attic and the basement.  He's a big believer in making a tight house.  We are going to use the heat/cooling contractor the green builder uses.  In fact, we used him to add Mitsubishi heat pumps/mini-splits to our in-law apartment.   The issue is that it's expensive.  We had the green builder in three years ago, and the estimate for the insulation/sealing was around 30k.  In the interim, I've done some stuff (super tight attic staircase, sealed a lot of the attic holes such as lights, etc.), but even with that, it'll be expensive.  And, we have a two zone heating/cooling system, with two air handlers.  We're going to try to change the attic air handler and AC unit into a heat pump, at least two stage system, but to add that to the insulation is quite expensive.  And, we still have another complete system to do later.

The other issue with insulation and sealing is that you can calculate approximate return on investment, but you can't gauge comfort.  Air sealing the house means more comfort.  For instance, we can keep the house a bit warmer in the winter.  I learned this winter (which was quite warm) that we were keeping our house quite cold in the winter.  It was nice to keep it at 70 sometimes instead of a high of 68 and much colder at other times. 

[Atlplasma]

ctviggen. $30K for air sealing and insulation sounds pricey. Before you spend those hard earned dollars, I suggest posting a question on the Q&A section at Green Building Advisor. Describe your objectives and your house (construction of exterior walls and attic/ceiling assembly) and indicate where you live. You will receive a ton of useful advice. The worst that can happen is the contributors will confirm the contractor's approach and budget.

You're absolutely right about the comfort issue. High efficiency allows us to keep our house around 76 degrees year round.

[WGH]

For comfort, the Low E3 windows are amazing. Summers in the Southwest can get brutal and the E3 glass minimizes heat gain and as a bonus there are no winter drafts with new windows.

When I remodeled my 750 sq. ft. house had to balance insulation with A/C cost (cost of unit + monthly bill) so ceiling has an R40, the existing concrete block house was outsulated with high density foam and stuccoed, and new windows all around. A 14 SEER Tempstar A/C-Heating unit is on the reinforced roof. During the last billing cycle Tucson had 24 days over 100 degrees, when I'm home I keep the temperature at 77 degrees. Last months electric bill was $91.00.

During the winter my body temperature, cooking, refrigerator and plasma TV pretty much heats the house.

[Atlplasma]

It can be hard to recoup your investment on replacement windows. High quality storm windows are often a better choice.

[JLM]

Yeah scary how easily most HVAC contractors literally use a couple simple rules of thumb to size residential equipment.

[WGH]

It can be hard to recoup your investment on replacement windows. High quality storm windows are often a better choice.

Probably true but you can do a lot of nice stuff to a small house without spending a lot.
My entire house has 7 windows. I went with the Marvin Integrity glider with LoE 366 w/Argon - total cost $3352.27
Replacing the windows was a no-brainer. Did I mention new windows are quiet? You wouldn't believe how low the ambient sound level is with new windows (think music room).

[Scott F.]

If you are looking to do insulation, you may want to consider this product rather than traditional OC pink.

http://www.insolcorp.com/

InifinteR is a phase change material that has some amazing qualities. We're getting ready to do a major addition to our house adding almost 1000 square feet. I've currently got a 3 ton, 21 SEER variable speed Carrier heat pump. With the properties of InfinateR, I'm estimating I'll be oversized after I add a few VAV dampers to the system and play with diversity a bit.

On their website, watch this video in particular;
https://vimeo.com/157063495

If you are an engineering geek in the building industry, this stuff is uber cool. I've got one of my commercial customers ready to install 120K sf on their buildings.

This stuff runs $2/sf in quantities under 5000sf and $1.50/sf in quantities over.

I'm wrapping as much of my house, garage, barn and condo as I can with it.