I am renovating four (New Jersey) apartments, 2 over 2.  The lower two have gutted ceilings.   I was looking at a btwn joist radiant install to heat the upper apartment.   The floors are nice so I don't want to go over them, and it's not practical to go under the joists of 1st floor.

Question:
Would it be possible to heat both top and bottom apartments with radiant tubing between the joists (1st floor has radiant ceiling, 2nd floor has radiant floor)? 

2nd question:
The whole reason I'm trying to find a way toward radiant, is that I'm interested in solar supplement.  Am I right in assuming solar better assists radiant than say, 140 degree baseboard?  I'm making rental units and want to find the greenest path...

Thank you!!

as long as your radiant is lower temperature than you indicate, it would be better for solar. Beware though. Solar heating is expensive. Solar DHW is usually more cost effective.

you can do joist above and ceiling below, just be aware that you are talking about 2 radiant layers with insulation between in that case. You can't do up and down from the same tubing... too hard to control.

Have you actually seen this kind of "double" install?   I'm interested in radiant mainly as a means of achieving a more efficient heating system that could better be integrated with solar.  Environmental stuff is a priority -- within my budget limits.   I probably could swing a diy install with a high degree of concentration; I couldn't afford to have the tubing professionally installed.  If I'm not convinced radiant will either, one, be comparable in price if I install the tubing myself, or two be significantly more efficient and environmentally friendly, I'll probably go with baseboard run at lower temps... 

About solar dhw -- by my calc a 6 unit 30 evac array, proposed by a local installer, will only save me 650 a year on dhw.    Not sure about how many more 30 tube evac I'd need to supplement radiant, but it seems like that would be the only way I'd get any real payback.   In this scheme I'd be paying heat and hw for the apt units.   

That backstory, which you've probably seen here and there on this forum, is that I'm trying to figure out the  best heating system for my renovation of a 6 unit building in nj - the two lower stores will probably be on forced air hvac.  The upper four units are apts.  The building is 75% gutted.   A very steep learning curve, with professional plumbers giving me totally conflicting info!! 

Low temperature baseboard is a contradiction in terms. Perhaps a professional design is in order. Free estimates are worth what they cost, thus the contradictory information.

Solar space heating in cold climates nearly always requires storage and 100% redundant fossil fuel backup...hardly green.

True low temperature hydronic distribution systems (operating below 140°F at design conditions) are really only achievable with radiant floors, walls or ceiling and with great care European wall panels. If you have natural gas, look to the condensing boiler (cleanest and most efficient form of fossil fuel conversion) with an indirect water heater (uses the same clean burner) and get a designer/installer experienced (perhaps even RPA certified) in radiant panels.

Of course it all starts with a heat load analysis from which viable panels and design water temperature are deduced.

strongly disagree with morgen on several fronts. I design 120 degree max temp baseboard systems regularly. radiant ceiling is cheaper, though, and more comfortable, for regular flat ceiling heights. and I would question what makes a mod/con boiler "green" when a "fossil fuel backup" isn't? would using fossil fuel only for backup be more green than using it for primary heat?

that said, without gigantic tax credits solar thermal is not a very viable heating source for most buildings. If you do a great job getting the envelope right, it can make more sense.

a 6 unit building trying to "go green" should absolutely consider solar thermal for DHW. for heating though I would guess... which is all anyone is doing without a more serious evaluation... that geo system may make sense, with rad ceiling or panel radiators. cheap zoning, max temps limited by water temp, larger upfront cost but greatly reduced operating costs. massive tax credits available for geo right now as well, I believe.

mod/cons are great if you're going with natural gas. but they are hardly the pinnacle of green design. Geo has issues too, but at a COP of 4+ you'd be doing pretty good.

what's the deal with panel rads needing 'great care'? do you mean that they have to be sized larger to emit enough heat from lower design temps?
i thought the panel rads were easy to slap in. what am i missing?

yes, you have to size them properly.

morgen is the German name for morning. I generally go my Morgan when not in Germany.

I have designed many systems using "existing" fin-tube baseboard, but admit I have never specified fin-tube, as it is technically not a radiant panel, (it is the cheapest form of hydronic emitter better suited to mobile rental properties). At low temperatures it is a very poor value as it takes a great deal of it to heat the same space, it takes up wall space like nothing else, it lose output (system efficiency) as it gets dirty (nearly impossible to clean), but it is cheap.

A ModCon is the Greenest of all fossil fuel appliances (and also the most efficient both in combustion efficiency and system efficiency) producing half the carbon footprint of coal (used to make the majority of electricity in these United States) with NOx and SOx so low that the State of California standard are still too low for the ModCon.

Domestic hot water is about 25% of the typical energy cost for a family of 4, ModCons cost less to operate that a Geo with resistance "backup".

with a COP of 4, then geo would have half the carbon footprint of gas, using your numbers.

cost of operation can only be determined with cost of fuels. There are many, many cases where mod/cons do not cost less to operate than a well designed and implemented geo system. Especially if you live in a cooling climate.

If we speak to the issue of return on investment the subject is moot.

I am quite familiar with the "magic" of ground source heat pump technology. As for a COP of 4. The vast majority of Geo will never see it. I am a mechanical contractor and chose more insulation and better windows over wholesale DIY heat pumps. It made more sense and fewer dollars; "free" cooling notwithstanding.

The cost of fuel and the distribution system (whether electric, coal, wood, natural gas, or propane) determines the final fuel bills.

If one looks at the capital investment and the footprint of heavy machinery, refrigeration, etc., GREEN becomes a relative term. I fully admit that “Geo” is the latest GREEN fad for the wealthy.

It is true that real radiant panels - properly sized and applied - will result in improved, perhaps even optimum, system efficiency.
But baseboard? Give it up man.

If you can run baseboard at the same temp as radiant, where was that downside again?

typically it's a second tier choice, but nearly every home in america with baseboard radiation installed could run 140 right now simply by going downstairs and turning their temp down and condense all year with no further adjustments. Getting to 120 is not *that* hard.... a little high output here, more footage there. Most panel radiators are 2/3rds convection or greater. Radiant floors themselves are 50%. Saying baseboard cannot be handled in a green manner is simply wrong.

again though, radiant ceiling is typically cheaper than 120 baseboard. and more comfortable, and it will run lower temps more of the time. we agree on that. But sometimes it's just not feasible. and baseboard works behind a couch and under tall windows with very little vertical clearance. not so great for panel radiators.

I never met a DIY heat pump, so I don't know what you're talking about there. well executed geo can definitely hit COP of 4. either way though, break even for COP 3 is 9x the cost of electricity per CCF of natural gas, and for COP 4 is 7x, and that's assuming real world 94% efficiency for the natural gas. Some markets go one way and others go the other way. While there are poor geo systems (and poor modcon systems) out there, I know contractors MEASURING COPs of 5+ seasonally on geo systems. That's not "fad math".

it's expensive. but on large loads, say a 6 unit apartment building for example, the economics can be quite attractive in many cases. even moreso if cooling is in the picture. Let's not forget there is more to mechanical bliss than just heat.

I'm with ya Rob, there's no magic or rocket science in getting baseboard to run at low temp- getting the heat out of the baseboard and in the room has a fairly linear delta-T (above room temp) & length function between ~120-180F input water, only steepening significantly when the delta-T between radiation water & room temp is under 25F. (If it weren't linear outdoor reset control would be very difficult to set up for baseboards, yet empirical evidence strongly suggests that its pretty easy.)

Systems that were (over) designed for 180F water in uninsulated drafty houses OFTEN deliver design-day heat at 140F or lower, once the basic the envelope insulation & infiltration issues have cut the heat load down to size. Such systems were often set to run higher simply to PREVENT condensing in the (cast iron/steel/other) boiler. I'm sure I've tweaked but a tiny fraction of the heating systems you or Morgan have, but even I've seen this movie multiple times.

<!--[if gte mso 9]> Normal 0 <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> <!--[if gte mso 9]> You're kidding right?

Baseboard output drops dramatically with average water temperature and is certainly not "linear" (perhaps a review of the manufacturer's data is in order).

The definition of radiant panel is "more than 50% of the output is by radiant rather than convective heat. No imagination can make fin-tube a radiator or an efficient emitter for that matter, unless are talking high temperature/cost of installation efficiency...cheap,cheap,cheap.

I don't think our friend is thinking multi-family.

I use outdoor reset (built in to all available ModCons) with all kinds of existing BB systems, but it is not ideal, it's just there. Making the best of a bad deal is not the same as good design.

Movies are obviously not real life. I have tweaked, added to, reset, and explained the shortcomings of hundreds of fin-tube baseboard systems. I have even torn out a few dozen and replaced them with more efficient and comfortable radiant panels. If you design a true radiant panel to high temperature you MAY get 2/3rds convective output (depending on the panel), but at low temperatures they turn into nearly pure radiant panels, i.e. high efficiency and high comfort. None of the many hydronic books in my library -dating back to the turn of the century- and particularly referring to fin-tube design - refer "PREVENT condensing" (in the trade we call it protecting). A simple bypass has always been the common method of keeping the boiler hot.

From his statements, it is clear that Rob has not seen many either. I am not even sure what he's selling today. The all high-and-mighty thing is getting a little old.

I'm all high and mighty when I disagree with your evaluation of mod/con boilers and baseboard's green-ness? getting a little touchy are we?

I sell high performance hydronic systems. typically not baseboard. but when baseboard fits the bill, it is used. low temp baseboard doesn't stratify that much, and quite simply it works. it's not as good as radiant ceiling or panel radiators for comfort, but it can run low temperature, it can do so efficiently, and in a good envelope especially the comfort downgrade is not huge. it is not a linear output relationship, but with 100 degree start temp on a reset curve it works just fine. Of course, many of my systems are designed for 110 max, and it's pretty hard to make baseboard work there. But 120 is not that hard. 130 is a walk in the park. Panel radiators cost significantly more initially, sized to run at those low temps.

But rad ceiling... it's often cheaper. and better. that's primarily why I prefer it, when it's an option. Rad ceiling doesn't seem to work all that well under 100 degrees either though. so I consider them both, practically, 100 to 120 degree range emitters when I'm designing in that ballpark. and radiant ceiling stratifies at least as much as low temp baseboard does. so you go ahead and tell me again about all those shortcomings of low temp baseboard compared to "radiant walls, ceilings, and panels". Make sure you compare to backloss while you do so.

I've never even vacuumed the baseboard in my leaky farmhouse, and it runs at 145 max, untouched from the day I moved in except for the mod/con boiler powering it. that's series BB... I haven't even home-runned the rooms yet.How' that for high and mighty? I have a leaky farmhouse, with dustry baseboard! Don't buy old buildings, that's all I have to say about that. I dream of gut rehabs. luckily our new shop is waaaaaaay better. and I spend more time there anyway...

I design around all kinds of heat sources, including geo and mod/cons. and geo works. In some markets it makes no sense at all. In some it makes a lot of sense. for small homes, it makes no sense. for larger homes/buildings, it can. But the answer is not always "mod con boiler" as you seem to pretend it is. the fact is a good geo system will use less energy than a good gas system, even factoring in production inefficiency and line losses. it will produce less CO2, not that I pay much attention to that, but some do. the only questions are whether the upfront cost is justified in cost savings or not, and how to design a distribution system that will harness those low temps, preferably without eating up some of your savings with big old fans blowing through hydrocoils. That question has different answers in different areas and different buildings.

rigid thinking: always the first mistake.

Nothing rigid about my thinking.

The ModCon is the finest, Greenest, gas-fired appliance and we generally agree on it's application and installation (I admire you for not selling them on the Internet). I just can't justify fin-tube...obviously, even though their thermal performance can be enhanced by outdoor reset and condensing technology, they are the very lowest of the hydronic emitters. I have consulted on several ModCon driven designs where fin-tube was the only emitter. When you can't heat the great room in Seattle you have a poor design and a poor application. We also agree on Geo and Solar. Everybody wants it, but few can afford it.

I am not arguing with the science of ground source heat pump, just the panacea. I considered installing one in my own house (DIY heat pump or Geo) the numbers didn't work for me and closed-cell foam did. I design a lot of solid fuel systems and back them up with ModCons and even electric boilers, but they all work for the customer.

In the east your options are more limited with high oil, high electric, heck high everything! Less flexibility, natural gas and cold weather. Guess I'm just spoiled.

Nothing rigid about my thinking.

The ModCon is the finest, Greenest, gas-fired appliance and we generally agree on it's application and installation (I admire you for not selling them on the Internet). I just can't justify fin-tube...obviously, even though their thermal performance can be enhanced by outdoor reset and condensing technology, they are the very lowest of the hydronic emitters. I have consulted on several ModCon driven designs where fin-tube was the only emitter. When you can't heat the great room in Seattle you have a poor design and a poor application. We also agree on Geo and Solar. Everybody wants it, but few can afford it.

I am not arguing with the science of ground source heat pump, just the panacea. I considered installing one in my own house (DIY heat pump or Geo) the numbers didn't work for me and closed-cell foam did. I design a lot of solid fuel systems and back them up with ModCons and even electric boilers, but they all work for the customer.

In the east your options are more limited with high oil, high electric, heck high everything! Less flexibility, natural gas and cold weather. Guess I'm just spoiled.

> Baseboard output drops dramatically with average water temperature and is certainly not "linear" (perhaps a review of the manufacturer's data is in order).

This sounds like a misrepresentation of the statement that it is fairly linear with respect to delta-T in the 120F-180F range or at over 25F delta-T.

Even low temperature radiant floors don't come close to being "nearly pure radiant".

Heat output for common fin-tube is not linear at any temperature or delta T.

It was designed as a high temperature emitter to replace "real", heavy, cast iron baseboard and radiators, giving up the radiant factor, high mass and most of the comfort. Fin tube baseboard "radiation" is not; it IS very nearly a "pure" convector, giving off the vast majority of its energy by moving air. From a comfort and output standpoint - using low temperature heat sources - it is the worst.

It is better than forced air, but they put that in mobile homes.

We have to deal with fin-tube every day, but don't have to specify it and the consumer should know what he is getting.

Unfortunately many "experts" don't know what it is.

All hydronic heat sources are better served by low temperature emitters, such as floors, walls and ceilings. Where large panels are not possible an oversized Euro panel will serve nicely at low water temperatures and radiant output above 50% making them true radiant panels.

Taking Morgan's advice, and consulting Slantfin's lit for some very run of the mill fintube    indicates ~20% reduction in BTU/foot/hour/degree delta-T (water temp against  the 65F air specified) dropping from 180F to 140F.  Not a perfectly linear constant ratio, but consistent, predictable, not ridiculously steep trend.

Take the top line (1gpm flow on their BL-75):
 
180F delivers 570BTU/ft (4.9BTU/ft for every degree above 65F air)...
170F delivers 500BTU/ft (4.76BTU/degree-delta)...
160F delivers 430BTU/ft (4.5BTU/degree-delta)...
150F delivers 360BTU/ft (4.25BTU/degree-delta) ...
140F delivers 300BTU/ft (4.0BTU/degree at 140F) 

You have a 0.65 difference in the delta-T above 65F at 140F that you have at 180F (75F instead of 115F) but it's delivering only 0.60 of the heat (300BTU/ft instead of 570F/ft.)  Not perfectly linear, but not a gia-normous divergence either.

I don't believe their calculated numbers at 120F, which show an INCREASE, where I would expect it to be starting to fall more steeply, but it's probably not off by 50% or anything like it.  Their calculated number at 140F may be slightly optimistic (mayhaps a bit too close to the BTU per degree-delta number they have as a hard-spec at 150F), but it's not likely to have suddenly hit a huge dog-leg in the performance curve.

I'd expect it's performance at 100F to be HIGHLY dependent on how recently they'd vacuumed out the dust-kittens, but 120-140F performance should be reasonably consistent- as consistent as it is at 180F.

Yes, convectors are never as cozy as radiators, and the low mass of fin tube makes for bigger more rapid temperature swings etc, I get that.  But deliver the heat with baseboards at low temp, dat kan.

that's cherry picking a bit, dana. for the intents of anyone in this thread, the sub-140 numbers are more relevant, and the curve does steepen there. Practically speaking, ballpark terms, you double your baseboard length (or equivalent output) from 180 to 140.. it doubles again, roughly, by 120. Doubles again, roughly, by 110. I consider 120 a practical limit to any baseboard system max temp as a primary heat driver (though for supplemental, you can go lower) because below that radiators start to make more sense very quickly and you're looking at radiant floor style costs... even if you had enough wall area for it all.

I'm not plotting charts on that, but that's the experience I've had with seigenthaler's sizing equations for fin tube, which I would certainly consider 'accurate enough'.