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Comment by Mvandenbergh | Hacker News Reader

Nobody will build a heat-pump system with an on/off control system like that because the performance will be awful. Certainly not an air-to-water system.

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It already exists. Check out Mr. Cool Universal and Gree Flexx. Heat pumps that work with a normal thermostat exist.

Most of the info about this stuff online is trash because HVAC is the most toxic online community compared to any other contracting profession. One of the reasons highly efficient mini splits haven’t took off in the USA- the self proclaimed experts want to charge $2000 to drill a hole and charge a line set, so most people DIY.

I've often wondered why this is. My best guess is that the EPA cert (not actually hard to get) has been turned into some sort of weird quasi-guild-membership thing.

I can walk right in to a "to the trade" electrical or plumbing supply and they'll deal with me, no problem, no questions asked. With HVAC.. they won't even talk to you without an EPA number, even if you're not buying refrigerant.

DTC for whole house systems, if they can make the regulatory side work and provide a good customer experience, is the most important part of this.

I'm a potential customer for DTC/DIY installation, but I think that's a pretty small slice of the market. Many of my friends are entirely willing to drop $4-5K for a single zone mini-split install (that's $1-1.5K of equipment and 2 hours of labor) and wouldn't dream of drilling a hole in the side of their house to save $3K.

I recently got quoted $17k for 2 zone mini split. I bought the tools, instructions, and watched youtube and spent $4500 total. At that savings, I don't need a warranty. I can just buy and install another system if it fails.

Can you explain a little more what you did? Just a little bit, like what brand, did you replace an existing home system. Who did the electrical, did you need duct work? I already have a forced gas system, you can just connect it up? If I only had say 4-5 rooms on one story it would be a lot easier.

Lots of good YouTube videos and good DIY HVAC content on garagejournal.com (the latter will have good discussion on brands as well as DIY installs).

For a case where you have a ducted gas furnace, you are probably better off with a traditional A coil evaporator, especially if you want invisible in the living area of the house. Those are not as DIY-friendly (but anything is DIY-able if you're skilled and bold enough, willing to learn, and willing [or eager] to buy some tools :) ).

Durastar 36k Dual head unit from ACwholesalers, buy 2 stage harbor freight vacuum pump, micron gauge from amazon, a bunch of manifolds, and fittings and adaptors from amazon, some NICE shredder core extraction tools, a NICE line set flaring tool, a pipe cutter, pre-insulated line set, 14/4 cable from outdoor unit to indoor units, 5/8 AC condensate pipe from indoor units outside, lots of zip ties, pipe wrap, and line hide. I pre-provisioned a 40amp breaker and an outdoor disconnect/breaker panel (and an extra 120v GFCI plug so i could easily run the vacuum pump). Sub-panels are your friend.

I used all Aluminum SER cable to run the sub panel and a copper whip from the outdoor unit to the breaker (terminals on the AC unit are rated for copper wire).

If you had a forced air gas system, you can get a heat pump coil and condenser to replace the AC unit. ACwholesalers has those too. If you are able to, you can add one to your system and run "dual fuel" where the heat pump runs down to about freezing, and only kicks on the gas for heat when it is outside the efficiency range of the heat pump (model dependent).

My house is annoying to condition. It was built in 1987 by people who had interesting notions about efficiency, space usage, and material selection. As a result, the surface area to volume ratio is pretty poor and it is not very efficient. the duct design is...TERRIBLE...and so a lot of the house wasn't served well by the HVAC.

I added a mini split to address the considerable heat load on the southern side of the house, and am working to replace the air handler and duct work entirely for the rest of the house.

Central air can do several things mini splits can't do, and that's why I want to keep it instead of just adding 4-8 more zones of minis splits, which would be WAY easier. 1. Air filtration, 2. Fresh air intake 3. Humidification 4. air mixing. it also seems to be the cheapest way to solve heat/cool + the things I just mentioned. Even with ducting. Design/Sizing/install is worse and harder. Leaking/poorly insulated ductwork can also cost a lot of energy and so takes a lot of effort to prevent.

HVAC as a mechanical system in homes is pretty awful, and the load calculations are frequently not well in line with the "theory" of system capabilities. Static pressure, air exchanges, etc all play Major roles in system sizing and make it very hard for technicians who do not live in a house to accurately evaluate the "real" load vs the theorized one.

when dealing with HVAC you either have to have a friend on the inside who has a license for mechanical or you have to buy everything on eBay... because you're right most of the supply houses won't talk to you unless you have an HVAC license of some sort, That's why most of the stuff I get is on eBay.... things like capacitors, blower motors, heat strips, R410A refrigerant etc either eBay or Facebook marketplace is the best place for it.... and then being in the house rental business I'm constantly buying this equipment and then just having people install it because it's just cheaper that way.... I save about 5 to $7,000 on average per install doing it that way

Here in Japan, every home store and electronics/appliance store sells mini-split HVAC systems directly to consumers. It's no different than buying a washing machine.

Yup, and a vanilla install will cost say 150$. Non vanilla installs still exist on the price list.

Mini splits transform HVAC into Lego, and a competitive market for install is the future.

This is different problem though: contractors just don't want to do small jobs since it doesn't make economic sense to them. Try to hire someone to paint single room or install single outlet, etc. and you'll see it is nearly impossible.

Thus the bill for the small job is outrageously high.

$50 says their units are the same units that the Mr. Cool and Gree Flexx units come out of, just with a fancy panel.

As a backup option, the incumbents already make this. Carrier Infinity is a good example. Proprietary protocol (RS-485 based, so it can run over existing thermostat wiring) between the smart thermostat and the furnace, and between the furnace and outside condenser unit. Even with all these smarts, there is still a fallback mode provided with a regular old dry-contacts control wires that can hook to any standard thermostat. Yeah, the system won't operate at peak performance, but it will operate, and that's very important when every HVAC tech carries a standard thermostat with them, or even uses basic jumper wires, in an emergency until they can return with correct parts.

Heatpumps are essentially pretty dumb devices at core. They use 24v AC for control, there's a reversing valve contactor to control if it's heating or cooling, there's a contactor for the fan, and one for each stage of the pump. Maybe there's another contactor for the emergency heating element. If you are fancy you might have contactors for UV sterilization, humidification, and/or dehumidification.

Literally the 'smartest' part of my HVAC system, beyond the thermostat, is the blower fan. It's a variable speed motor and has a speed controller integrated into the motor housing with multiple 'taps' that let you control the fan speed in steps. It's configurable if you have the programming hardware.

My Carrier wall unit has a button for manual operation:

> MANUAL CONTROL is intended for testing purposes and emergency operation only.

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