Hi, New to the forums, in the Monadnock area, NH

I've a triplex and put in two radiant under floor systems about 14 years ago for my upstairs units since I rebuilt the lower unit and had all ceilings open.  Both are fired by ordinary oil fired water heaters.  One uses a homemade copper tube in tube heat exchanger system, low pressure, isolated loop.  I used 7/8" partially crosslinked poly (I think) tubing with aluminum spreader fins from Radiantec.  The other is high pressure (heating loop uses potable water and runs through the water heater) (~45lbs psi) that runs through a separate oil fired hot water heater (purge on hot water use to avoid Legionairre bacteria) and also has worked fine though I developed a tiny leak (made a ~6" spot on the ceiling below and never became an "active" drip) which leaked one season and oddly, did not leak the second season.  I'm planning on changing this to an isolated loop also hoping that by dropping the pressure to ~3lbs psi it'll keep the stopped leak stopped.  It's easy enough to cut a section out and replace a few feet but I don't want to have to redo my living room ceiling!   People laughed at my systems 14 years ago but my tenants love them! (each about 650SF)  My only real hassle has been to change out the mixing valves every 6 years or so.

I want to change the downstairs unit (which I live in currently) and which has nice steam radiator heat but an old circa 1960 slant fin boiler (which I was told in 1982 would "definately not last one more year) which hums along and will for another twenty years but I cringe at its efficency.

My power company has a $1000 rebate for AFUE 90 and a $1500 for a 95.  I've heard so much bad for so long about 95's that I simply don't want the extra $500.  There must be some reliable, long lasting oil-fired units that would let me do a tube in tube (hey they are cheap to make and last forever, and never clog) exchanger and run 3 or four loops with a hot water take off of some sort. (storage tank?)  I'll likely use Radiantec's 7/8" again, it works, it's cheap, easy to install and from my cellar it's pretty easy to install.

Can anyone recommend an AFUE 90 oil fired unit and suggest the best way to take off hot water for a 1200SF fairly well insulated unit?  I also wonder about a larger oil fired ordinary hot water heater to run the whole busines, that's what the two small units have and it works beautifully but I imagine the efficiency is not great.  I just replaced both water heaters after 14 years, heck $800 every 14 years works for me (note I replace anode rods every 4 years!) as we do have chlorine here.  12-14 years on a water heater thrills me.

Have things gotten to where the AFUE 95's are worth it?  I want something that'll last 20+ years.

Thanks.

there is no benefit to 7/8"... it's not as cheap as 1/2" and it's nowhere near as easy to install and contrary to the marketing BS surrounding the product, output is not significantly improved with the larger pipe. go small and smile at all the benefits.

I suggest you get off oil if at all possible... If that's not feasible, then with the size you're talking about, you're talking tank heater, like a Bock. with heat exchange, of course. If you do a boiler with indirect tank with most models you'll waste about a tank of oil a year in wasted heat from DHW cycles in the non heating season. that'll eat up your $1000 rebate pretty quick. Also they just don't make boilers this small, and if you want to skip the tank of waste a year you'd need purge controls on the boiler. I would use a combined reset and purge control like tekmar offers in that case.

I'm not even aware of any 90's in oil that people consider reliable... but I'd love to hear experiences to the contrary.

A 1200' well insulated house in the Monandock region of NH can be heated with a 1 ton mini-split air source heat pump (Fujitsu AOU-12RLS2-H, or Mitsubishi MSZ-FE12NA, either of which are designed to run at -13F or lower), at less than half the operating cost of an oil fired HW heater. It's not as cushy as radiant floors, but it's far more comfortable than heating with ducted forced hot air. The installed cost of either of those mini-splits is usually under $4K for the whole shebang. If your actual heat load calls for the 3/4 ton versions in those series you're looking at under $3500. If it's actually a bit higher than 1 ton, there's a -15RLS2-H, or a -FE15NA available to fill the bill which runs about $4.5K installed.

You'd likely need some resistance auxilliary heat such as radiant cove heaters or electric panel radiators for rooms doored off from the common areas with convective-air access to the mini-split head, but used judiciously (or with set-back or learning thermostats) won't have much impact on the total power bill, as long as you "set and forget" the mini-split and let it modulate with load, maybe even setting a bit higher than you would a radiant heated room to let it conductively heat the doored of adajcent areas. Done right your net seasonal average coefficient of performance ( COP) on the the mini-split will run 2.5 or better, and your shoulder season COPs will beat all but the very best geothermal heat pump systems.

Download the policy piece on this page, for how/why this is a good idea when oil, propane, or electricity are your primary options:

http://www.rmi.org/Knowledge-Center/Library/2013-05_HeatPumps

See also:

http://fergusonhvacchicago.com/wp-content/uploads/2013/03/9-12-15RLS2H-Sell-Sheet.pdf

http://www.mitsubishicomfort.com/media/359053/m-series%20brochure%203_11-r_pages.pdf

Most 600-700' apartments in this area could can be heated primarily or solely with a 3/4-ton to 1-ton cool-climate mini-split like these. Radiant is super-nice from a comfort point of view but more expensive to install. Mini-splits don't suck on comfort, and since they also provide quiet very high efficiency air conditioning, might be a real plus in a rental unit come July (or a coupla weeks ago when it was bumping on 90F or a bit higher.)

Without a lossy steam boiler heating up the basement, air-sealing & insulating foundation will make it more comfortable down there, keep the first-story floors more comfortable in winter, and lower the overall heat load on the building, while limiting the summertime mold potential. Insulating foundations isn't like the rest and needs to be done right, but need not be expensive or complicated. If you go that route, check back for details (or reasearch it carefully on sites like this one, Building Science Corporation's archives, or greenbulidingadvisor, etc.) (There's a rigid foam insulation reclaimer operating near you in Winchendon MA that could make it a VERY cheap DIY- cheaper than virgin stock batts in studwalls.)