The majority of small two stroke engines do not have an intake valve. They are piston ported. The piston passing the intake port functions as the valve. During the compression stroke, the piston rises creating a partial vacuum in the crankcase. As piston continues to rise it uncovers the intake port, drawing air-fuel mix into the crankcase. Above the piston, as it rises, the air-fuel mix is compressed, until it is ignited at or near TDC. The piston now starts down in power/scavenge stroke. As the piston moves down, it covers the intake port, preventing backflow of air-fuel into the carburetor. Pressure is also building in the crankcase as the piston falls. Also the piston also uncovers the transfer port, which causes air-fuel mix to flow into the combustion chamber and forces the previously burned mix out the exhaust port and into the muffler. Reed valves are used in higher performance engines (karts, some chain saws) to allow more aggressive porting and timing designs and eliminate backflow to the carburetor. Rotary valves are also used to achieve the same high performance. Rotary valves are more expensive and tend to be used in high performance motorcycles. Kawasaki was a big believer.

Wow! A rare case where the aesthetics part of the performance-aesthetics-economy: pick-any-two limitation is not a factor in hood selection. But first, given a sealed household, I would strongly recommend obtaining a furnace kit to use outside air. This will avoid the possibility of the MUA system not working perfectly and the hood causing negative house pressure and hence backdrafting of the combustion appliance. I know that such devices exist for Beckett burners, and would guess that there are adapters for other burners. As the OP correctly notes, a 200 cfm ERV is not going to cope with a 1200 cfm vent hood. (Actually, what would happen with a sealed house is that at full power, the hood would pull the cfm the ERV would let through into the now minus a couple of inches w.c. house pressure.) So MUA is essential, and in the mid-Atlantic region would be pretty uncomfortable in winter if unheated. Depending on one's tolerance for heat and humidity, cooling in summer might be optional or not. We are starting to get into the realm where performance-economy, pick any two is applicable. MUA can be roughly characterized as passive or active. By passive is meant no fan in the circuit. Active uses a booster fan to keep the house pressure stable. No-fan only works for simple ducting with a vent hood air flow controlled damper. (A recent post here provided some sources for these.) If a filter is used at 1200 cfm (or whatever flow actually could be pulled with all the doors and windows open, then the house pressure will drop. One can see on websites selling filter packs that the pressure drop at such flow rates is too large for combustion appliance safety, which require negative pressures not be greater than 0.03 to 0.06 inches depending on appliance type. Active is needed to overcome the filter restriction. It may be needed to overcome heating heat exchanger restriction and/or air conditioning heat exchanger (expander) restriction. The difficulty with active is balancing the MUA air flow rate against the variable hood flow rate such that the house pressure is near zero. This usually requires a control system of some sort, and can be a "project." What to do? What to do? Only one free-of-processing-controllers active MUA has occurred to me. In the simplest embodiment, the hood control is connected to two parallel wired identical fans, one in the hood exhaust path and one in the MUA path. Then the two will (try to) operate at nearly the same flow rate at every control setting, and one only needs to adjust the MUA duct restriction until it matches that of the hood path. More exactly, adjust the MUA path so that house pressure falls very little as the hood is turned on. Note that this doesn't account for bathroom fans, fireplaces, or other exhaust flows not due to the hood. In such cases, PID control of the MUA fan would be needed. In my case, due to a 1500 cfm hood, 1000 cfm over-oven vent, fireplace, and three bathroom fan household, I am building an active MUA that will use an axial blower in the 2000 cfm regime. It has to overcome the pressure loss of its intake vent, its filter, and its heat exchanger (which is hot water pumped from my oil burner). Control is via a Fuji PID controller operating from a BAPF differential pressure sensor. The motor power control is not yet selected, and a lot of sheet metal action is still needed, along with further attic revisions that I seem to have trouble getting to at the needed rate. I recommend the OP and/or his HVAC person read the "Kitchen Ventilation Systems Application & Design Guide" that may be found at Greenheck's web site. It periodically moves around, URL-wise, so a Google search by name may be fastest. Greenheck or one of its competitors may be able to provide what you need for considerably less agony than a do-it-yourself HVAC project would. kas

Short cycling occurs when the AC has much more capacity than the heat load of the house. The AC turns on and cools the house very quickly. Quickly could mean 10 - 20 minutes. The short amount of time does not allow the AC to lower the indoor humidity. You feel cool but your are still sweating. It becomes a problem if you live in an area which has high humidity. The 5 ton capacity refers the size of the condenser. The blower in the air handler is adjusted to work with various condenser sizes. Your handler may be able to work with a smaller condenser. I don't have a good feeling about the installation contractor. He has done a poor installation and appears to be avoiding you. What type of warranty does he provide? Make sure you document the problems and stay on top of him.

gb85, Most, if not all, horror stories you found in your research were posted by people who didn't know what they were doing and proved it. For reference... SADDLE VALVE = BAD PE (polyethylene) TUBING = NO PROBLEM Any appliance that can use PE tubing can use copper tubing but will/may require different fittings. All one needs to do anything is the knowledge and the tools. Lacking either and considering the expensive damage a mistake can bring you should consider a plumber and think of the cost as tuition. That said, what don't you like about your water? Are you on a well or water system? what are you wanting to filter for? Additional faucet at the kitchen sink or ice maker/water dispenser in the fridge also? Is your water softened?