Hi all. This is a repost from the piping & plumbing subforum since I didn't get any replies there. I'm wrapping up a massive foundation project & remodel in which we've built an in-law apartment on the ground floor, are adding a boiler for heating, and am replacing/upgrading all of the plumbing. With the walls open, this would be a great time to add plumbing for a solar water panel on the roof. Below is a pretty basic diagram of our setup: a 3-story house with the boiler / utility room on the ground floor, and bath & laundry in the main living spaces on both the ground and 3rd floors. My questions: 1. Being a line pressure system (no pumps), I imagine I'd want the largest diameter practical to the roof to maintain head pressure? 2. The distance back down for the solar heated hot water will be approximately 40 feet. How do I size this line properly? - if I go for a large diameter, I'll be storing a lot of water in the line and losing heat between cycles. - if I go for a 1/2" line, that will decrease heat loss, but will it restrict head pressure (since this pressure is feeding the DHW supply for the whole house)? 3. I've read "COPPER ONLY / NO PEX" for a number of the installation instructions for passive solar water panels. But PEX offers some insulating properties that copper doesn't. If I'm using PEX elsewhere for 180° heating loops, why can't it be used on the return from the solar panel? 4. Note that I drew in a small water heater in the attic for "instant" hot water in the upstairs bathrooms, which are a 50' run from the ground floor water heater. Is it plausible to incorporate a feed from the solar panel directly into this area? Maybe a mixer valve just after the small water heater? I'm having trouble envisioning what possibilities exist here, including the deletion of the small water heater? [COLOR="Navy"] * I've done some digging around since I originally posted this, and am thoroughly confused how to temper this water. Mixing valves have a "hot" and a "cold", but how does one handle a situation where the supply from the solar panels may be as hot as 200°+, or as cool as 50°? Would I plumb it to the inlet side of the water heater, let it mix in the tank, then temper it with cold on the outlet side?[/COLOR] [IMG]http://www.booboodog.net/images/house/hot-water.jpg[/IMG]

My home has oil heat (hot water baseboard with furnace in basement) and an oil fired hot water heater. The water heater has its own burner to heat the water in the tank. My best guess is that the water heater is about 15 years old, based on the Energy Guide sticker on the tank that quotes 1994 oil prices. I have 2 questions: 1. Should I think about replacing the water heater? I have no idea how efficient it is, given its probable age, and I am also concerned about how much longer it will hold up. It works fine for now, and it checked out when inspected and serviced by a technician recently, but I feel like it's nearing the end of its expected lifetime. 2. If I replace, is it better to go with another oil fired tank, or a hybrid electric like the GE GeoSpring? I live in Southeast PA, and the water heater resides in the basement next to the furnace. I feel like the hybrid electric could be less expensive to run, and I think it's cheaper to install after tax credits and rebates. The house is just my wife and I (for now), and even in the future I don't expect that the demand for hot water will be extreme. I appreciate any help. Please let me know if you need additional information. Thanks.