Building a residential monolithic dome assemblage totaling 7000 square feet consisting of the following 4 concrete domes: 1) main living area dome of 3000 square feet with second story used throughout the day 2) game room dome (center of residence) of 1000 square feet used one hour a day 3) garage dome of 1660 square feet used 10 hours a week at two intervals of 5 hours each 4) covered patio dome used an hour a day (probably no radiant floor heating to this dome) All domes will have 5" concrete floors. Construction has not begun. The building is in the permitting phase. Electricity is available at the property, and propane is readily available from several distributors in town. Location is Rochester, WA, in the pacific northwest - two season climate with a lot of rain (usually, although this year was an anomaly). I want to nail down the heating method now. I want to be as green as possible and am willing to pay up front for reduced on-going bills. Solar is not a good ROI in this part of the country so that is out. I am leaning radiant floor heating, 1/2" pex-al-pex with a tankless/on-demand propane water heater. One zone for the main 3000 sq ft dome, one for the game room, and one for the garage. I would like the water heater to provide both hot water to the floor via pex in the slab and to the fixtures. The above is what I have come up with, but I fully recognize and acknowledge that I am not an expert on architecting radiant floor heating systems. I wanted to ask those here with more experience... what type of system would you spec for this type of situation? The layout of the house can be seen here: http://loraxhomes.com/projects/rochester/ Respectfully, Scott

Ductless air source heat pumps work great in your climate, and would be dramatically cheaper than heating with a radiant floor & propane fired boiler. It's possible to do hydronic radiant floors with air-water "reversible chiller" heat pump, such as a Chiltrix (http://www.chiltrix.com/ ) or Daikin Altherma (http://www.mechanicalairservice.com/images/pdf/Altherma%20Brochure.pdf ) Technical support and design for that type of equipment may be hard to find though, and there are 1001 ways for a DIYer to really screw it up buying more hardware than needed, while taking a hit in efficiency. Hire a pro. Century Heating in Portland OR has experience with the Altherma, don't know if they would travel as far as Rochester- it's a bit of a drive, but they do cross the river for the nearby WA counties.

Until and unless you've done the heat load math, it's not really possible to specify the equipment. With less conventional construction methods & shapes getting accurate load numbers can be more difficult- hard to just plug them in to a standard Manual-J load calculation program. Hopefully you have an archictect/engineer that is fully up to speed on that (?). But knowing the load is really a firm prerequisite for choosing the heating method & equipment.

With spaces that only need to be heated intermittently radiant slabs are a terrible choice, due to the high thermal mass of the slab and the time delay incurred, and the total BTUs abandoned just to cover a short term demand.

Tankless propane water heaters have higher up-front & maintenance costs that could make it more expensive than a plain old electric tank on a lifecycle basis. Your grid is pretty green in WA (greener than a condensing fossil-burner), and unless you're insisting on propane for some other reason, all-electric is the way to go. Using a tankless propane water heater as a BOILER for a radiant floor is an even weirder can of worms. It can be done, but you're better off by far going with a condensing propane boiler, since it is designed for the application. (That said, have been heating my own multi-zoned house with a tankless water heater for the better part of a decade without problems, in part because I did all the math first. Most of one size fits all tankless radiant designs available from web stores are pathetic pieces of junk, not to be emulated!)

There may be tankless combi-boilers that would work OK in your application, but without the load numbers and some sense of your domestic hot water heaters it's impossible to make the call.

Even so, it's far greener to use modulating heat pumps, which will also have a substantially lower operating cost in your climate. I have relatives in Kitsap County and others on Whidbey Island heating with ductless mini-splits. The folks on Whidbey claim laugh every time they pass a propane truck now, since they used to heat with high-priced island propane.

I second what Dana wrote. I think all electric would be the way to go. If you truly want HR floor heating, I think the Daikin Altherma would be my preference. An electric boiler might make sense too if you are willing to trade electric boiler simplicity, lower acquisition cost and higher operational cost for the heat pump lower operational cost. If so, you might be able to use NextGen appliance to truly simplify your HR installation and operation:

NextGen

As Dana indicated, you will first need to accomplish a proper room-by-room heat loss analysis before designing your heating system. We have free DIY software on our website to accomplish that if desired:

Borst Heat Loss Analysis Software

sailawayrb: Have you ever run the load calculations on a dome? Calculating the surface areas accurately on intersecting domes can be somewhat complicated.

We don't know if these are going to be cast concrete vs. some other method, insulated on the exterior, interior or both or to what level, and the insulating value of the air films won't be the same as for planar walls & roofs. But figuring it out would be a fun enough project for a bored enginerd! :-)

With preliminary load numbers it'll be possible to zoom in a bit on what heating options make sense (financially or otherwise) and which don't. Before then it's just idle armchair speculation.

Yes, you just have to get the exposed area and working in spherical coordinates is best way to handle the intersecting dome and such. Seems like more and more folks are doing domes in our neck of the woods. Some of these are even underground...like one of our neighbors. Their biggest complaint is everything that goes on the walls must be customized...like the kitchen cabinets... I have never been a big fan of domes in general and especially living below ground, however, they do have a very nice place and they seem to like it. We are actually care taking their place right now as they are away on vacation.

Thank you both for your answers. I'm working on getting a heat loss calculation. This is really difficult, as none of the traditional heat loss calculators factor everything about this dome in (room shape, materials, etc), and this is actually 4 domes. I mean, how to calculate square feet of wall area? I know... hire a professional to do this. Your replies have given me enough to conclude that the right way to heat the garage (when I am working in it) is probably just a plain old space heater. Same for the game room. Both will be just large empty dome rooms. So it has allowed me to narrow my focus to heating the 62' dome which is the real living area, that will get used just about evenly all around, as far as time spent in each area. Sailawayrb... I really like that NextGen boiler! I will still take any additional input and ideas on this topic. The only reason I originally leaned towards propane is because that is what someone else I know with a dome in the same area here is using to heat their radiant floor hydronics system.

Well, I wouldn’t totally dismiss condensing propane boilers without first doing the ROI calculation using your actual fuel cost numbers...but I think I know how this will go... BTW, we also have free DIY software on our website that will calculate the various operational costs for the various heating sources and fuel options:

Borst Integrated Heating System Performance Software

I will also add and perhaps even suggest...if you think you will need/want AC...even in WA, man-made global warming is coming...ductless ASHP mini-splits are a very attractive solution. And maybe look at radiant cove heaters for those not so often heated areas...quick heat for short period it is needed.