The long axis of the house runs East West with bedrooms and bath at the East end; the great room at the West end.

The one company we asked bids from recommended 5 - 9,000 Btu heads. Two heads to be located in the great room and one head in each of the bed rooms. Thus, he's recommending a 3 3/4 ton system! Isn't that a bid over kill? The bed rooms need 3,000 Btu each and the great room needs 10.000 Btu so how does the system work to compensate for overloading in some areas? And what does that do for efficiency?

Posted By agagent3 on 14 Apr 2015 05:09 PM
The one company we asked bids from recommended 5 - 9,000 Btu heads. Two heads to be located in the great room and one head in each of the bed rooms. Thus, he's recommending a 3 3/4 ton system! Isn't that a bid over kill? The bed rooms need 3,000 Btu each and the great room needs 10.000 Btu so how does the system work to compensate for overloading in some areas? And what does that do for efficiency?

The guy is completely fug-nutz, and you would be too if you followed his plan!  The turn down ratios are not infinite, and the standby losses are non-zero.

He's a hack- run away! This may solve his boat payment arrears problem, but it's not something to heat & cool your house with.  Four tons of compressor for a heat load that would have margin with 2-2.5lbs of compressor is simply ridiculous.

A single 3/4 ton Fujitsu 9RLS2 (or RLS2H, or the new RLS3H series- which is significantly more efficient)  can deliver 14,000 BTU/hr @ -5F (11,000BTU/hr @ -15F).  But it's minimum modulated output at your average winter temp is still over 2000 BTU/hr, and way more than the average load in a room with a peak load of 3000 BTU/hr.   The  12RLS3-H or even the 15RLS3H wouldn't be overkill for the great room, and both of the bigger units will modulate just as low as the 9RLS3H, despite their higher maximum output capacity. The 12RLS3H  is probably the right choice for the great room if your outside design temp is under -5F, the 9RLS3H if it's closer to 0F.

A single 3/4 ton Mitsubishi FH9NA will deliver over 9000 BTU/hr @ -5F, but has enough at 0F to have you covered for the family room if that's your outside design temp.   Even the 1.25 ton FH15NA would not be overkill.  If the design heat load is 10K and your outside design temp is under -5F, go with the FH15.  If your design temp is 0F, go with the FH12.

The three bedrooms can be heated with a single 1.5 ton  Fujitsu 18RLFCD mini-duct cassette on it's own compressor serving of them. Use a home-run duct configuration to the cassette rather than plenum & branch, with the flows designed for the relative calculated heat loads  (they're  different enough- it looks like BR3 needs about half the flow of BR1.)  There will be some flow tweaking to achieve good temperature balance, but this is fairly standard fare for duct designers.  Unfortunately the Mitsubishi mini-duct cassettes crap out on capacity by +5F, and probably wouldn't cut it at low temp.

Dana1 you are the greatest! And we're running away from this guy fast. By the way he is the HVAC Manager. This type of company recommendation is all to familiar to me. My son and I have attempted to screen and look for the better HVAC people. I'm just flabbergasted! What happens to the consumer that doesn't wish to educate themselves? We Americans must be spending WAY more than we have to on building systems than we have to.

Great thread. Great Info. Thanks...

I had a similar experience with an HVAC contractor that told me what size system I needed over the phone! Without seeing the house, and completely ignoring my description of the construction, he confidently told me I would need a system that was 300% of what I actually needed.

This raises the point that evidently manufacturers are eventually going to have to produce smaller systems to handle the reduced loads of very efficient homes. The 9K in our master suite is way overkill, and we don't use it often. I would have bought something in the 4K range if I could have.

Thus the Manual 'J'.

I really dislike hammering on this point but where is the professionalism? Or is it just ignorance? I would think that giving the best advise and system possible is just good business. Or have we come to the point where we all need to hire an engineer for every major home system build/upgrade?

One last question for Dana1; what would home-run duct configuration to the cassette look like? Would one be using the space between trusses as a duct?

Basically the duct runs to the rooms are all individual, hooking up to a fatter duct plenum just before they hook up to the mini-duct cassette. This isolates the room-to-room sound transmission through the ducts, and also makes flow balancing much easier. The Fujitsu mini-duct cassettes can be installed in any orientation- sometime it's easier to install them vertically in a slightly thicker section of wall rather than horizontally.

Don't use panned joists as ducts (is that even allowed anymore?) At the flow rates you'll need you can probably get away with 5" or 6" round hard-piping as long as the runs are relatively short & straight. Even an insulated 8" round makes it between 2x10 joists. Unlike panned joists, hard pipe ducts are easily sealed & insulated.

So think about where the mini-duct cassette might live such that it keeps the duct runs short and fully inside conditions space, not penetrating the insulation or air barrier/pressure boundaries of the house.

I just received the quote for a 4 ton minisplit with 5 heads installed...$16,552.36! Whoa! And again that's for an exceptionally well insulated, tight new build of 1518 square feet in zone 5.

I've been paying $3-4,000 for single Mitsubishi Hyper Heat units, so it sounds in line with those prices. haven't yet priced the multi-head.

Welcome to GREEN living! The prices are in line with our own.

Like one of my contractor clients said about the cost of the, then new, condensing boilers; that will buy a lot of gas! or electricity in this case.

Sometimes the potential savings realized in good insulation can justify less investment in high efficiency equipment.

OTOH
IF the home including foundation and slab floor is insulated to Building Science Corporation's suggested R values (R40 walls, R60 roof, TG windows etc), and is very tight - under 1 ACH50 - we would typically use two units in a 1400 Sf home; one in the great room and one in the bedroom wing. An alternative would be three - add one in the master BR and one in the hall outside the other bedrooms. We do not feel that a separate unit is needed in every bedroom in the houses we build. Since we are not building your home, we cannot say that this would be ideal.

Thus the room-by-room ACCA Manual 'J'.

The plan is to build it tight and highly insulated. It will be on an insulated slab. From the research that I have done, two smaller units seem to be the norm for well designed homes.

The cost of going green reminds me of a discussion I had with a Monsanto rep years ago. At the time Round-up was selling for $40 a gallon in the US and $10 in Brazil. I asked the rep why, her reply, "it's what the market will bare". Recently I had a young man come out to service the air conditioner. We were talking about minisplits and their efficiency. He related to me a rich guy wanted one with a head in each room. The young man said that "it was unnecessary but hey, we'll sell him what ever he wants". Since the poor folks can't afford it seems it's a case of sticking it to those who can or to those who really care about the environment. I often wonder about the ethics or lack there of our business people, politicians and institutional leaders.

If giving people what they want is "sticking it to them"

I guess we are all lost. Is there a difference between a contractor charging a premium for more-than-standard equipment and the government using general funds to subsidize GREEN industries?

If you are in saving energy and or the environment you must be willing to pay the price without protest.

I am not protesting paying a premium for excellence whether it's a product or good sound advice. What I would hope for is honesty. Honesty is a cornerstone for building trust (and repeat business by the way).

I’m not certain I know the true mission and purpose of this forum. The name Green Building Talk connotes a sense of environmentalism. I view it as a forum in which ideas may be exchanged with the purpose of overall improvement in technique and building systems. I have picked up that same notion from the various discussions that have taken place. I would like to think that there are builders and building system professionals who truly want to save energy and lower carbon footprint; and yes, make a profit. Not a thing wrong with that. I’m uncomfortable with what I view as “deceptive business practices.”

As far as government subsidies go the fossil fuel industry is a HUGE recipient of tax dollars. Subsidies are useful to help get new industries going where the private sector is unwilling to take the risk and then end. The fossil fuel industry is long of tooth and should be weaned by now. I believe it was during the time of Lincoln when the railroad companies were heavily subsidize at the tune of $3,000 (1865 dollars) per mile on the flat plains and lot’s more once they hit the mountains.

9K mini splits are about $1200, they are so simple to install any one can put them in in 2 hours, but hvac contractors typically charge $3,000.

no question that if you want to build your own house you can save a fortune by keeping the huge profits the electricians, lumber yards and drywallers are pocketing and doing all the work your self. Should only take you a few weeks and all it is is nailing together a bunch of boards and stringing wires and pipes. Simple. If everyone did that the prices of houses would drop dramatically. And you can buy everything on the internet, delivered by drone.

Posted By gosolar on 16 Apr 2015 06:08 PM
9K mini splits are about $1200, they are so simple to install any one can put them in in 2 hours, but hvac contractors typically charge $3,000.

I would disagree with that on numerous points. First, they are not, "simple to install anyone can put them in in 2 hours" because it is not simple. Second, most manufacturers will NOT warranty a DIY minisplit install. Especially an unlicensed, untrained, DIY person. Thirdly, whatever "money" you think you saved will be lost because a qualified installer carries a 7-10 year warranty on the minis but a DIY carries with it a 0 day warranty, maybe a 90 day if you are lucky. Finally, if you can install a mini split in 2 hours then you are not a DIY person and even professional people who puts them in every day CANNOT install them in 2 hours, impossible.