I'm adding a zone to heat a room over my garage. 16' X 24' with 9' ceilings. I have room on one wall for the baseboard heat (hot water). The rest of the house has Haydon units, I plan on using Slant Fin, opinions?
The local supplier has an 8" high output unit or I can use two 5' units. I have room for 10' on the wall. Would two 5' units be better than one 8' high output. Your help is appreciated. I'll watch this thread closely for your input and to answers any additional questions.

 

Plymouth, MA, eh? How very seasonal. You size the baseboard by the heat loss. Need to know how much insulation in floor, walls ceiling, what kind and square footage of windows, doors, etc. There are simple programs on the web for this small a job. See

http://www.crownboiler.com/educate/heatloss.asp

for one example. Or you could get a whole package at

www.slantfin.com/he2/

For Plymouth, I'd suggest a design temp of 5F.

 

Just offhand, from my limited knowledge, that doesn't seem like enough baseboard to me... figuring 10 feet at what, 550 btu/ft ? How much glass, and how well insulated ?

Wow! 171 Mbyte download on the Slantfin ? yikes!

I think the slantfin you get at the big box stores is "consumer" grade stuff, lighter gauge cabinets mostly I would think. You can find better baseboards, and I'd like to hear the other guys opinion as to what b/b to buy ... that said, it's been working fine in my place for quite a few years now.

 

The room is very well insulated and has two windows both high quatity Low e.............. and again insulated well. There is a knee wall on the outisde wall that I'm installing insulation and a vapor barrier tonight. There also two ceiling fan to help move heat from the ceiling down.

 

Talking about that high output unit ... you sed 8" ... you meant eight feet, right ? Do you have btu numbers on that unit ?

If I was gonna use slant fin again, I'd bite the bullet and go with the multi-pak 80, especially if the baseboard was going to be exposed in an active area. If you were hiding stuff behind furniture, then the lower end stuff is probly gonna stand up over the years. It's also higher output.

There's no way you can run at least the length of one outside wall ?

 

Numbers man we need numbers. You're probably on the edge of being underheated, esp. over a garage. R-values in floor and ceiling. Sizes of windows. Size of door(s). How many walls exposed to the world, how many attached to any existing structure.

Multipak80 goes nominally 840 BTU/hr/ft at 4 gpm so call it 800 after piping losses, etc. on the way there. 800*8 = 6400 BTU/hr if you go with an 8-footer, 8000 BTU/hr if you get a 10-footer.

For reference, I have a 24x13 room, 9'6" ceilings, similar design temp. R13 walls, R38 ceiling, located over heated space, Low E windows. Needs about 8200 BTU/hr at design. Your heat loss will likely be greater.

I suggest doing the heat loss and if you end up at 8k or greater, either find more wall space for baseboard or go with a different form factor (cabinet rad or panel rad).

 

If I calculated correctly I get 7419 for heat loss. I only have one option for placement of the baseboard. The only reason I was going to use Slant Fin was because of quality. If there's a better unit at a higher cost I'll do that. I'm not trying to cut corners. The local plunbing supply house (not a big box) said baseboard units only come in 8' lenghts not ten. He suggested using two 5' baseboards. Any suggestions??
Again , thanks for all the help.

 

DIYJohn:

The numbers don't add up; you're going to end up freezing over a garage in Plymouth if you don't do one of the heat loss calculations, as suggested.

Even the simplest HLC sites below are calling for 15,000 btu/hr to 20,000 btu/hr for this over the garage deal.

The internet forums are replete with people complaining they're living over a garage & can't figure out why the baseboard isn't doing the job.

The high-output baseboard @ 800 btu/ft by Heatrim, Slantfin & others are calling for 18 to 25 ft. to keep the room warm & cozy.

You're over a freezing garage, brother; do the HLC's. & save yourself some grief.

http://www.burnham.com/heatloss1.cfm
http://www.heatload.com
http://www.crownboiler.com/educate/heatloss

 

DIYJohn, I'm just over the bridge from you. About a third of my first floor is over the garage. It's the still the coldest part of the house (especially the outboard end over the garage doors) and I've insulated/sealed the heck out of it. I think 7419 might be an underestimate unless you've got 2x6 walls with max rated insulation, 2x12 floor joists with max rated insulation and a very thorough infiltration/sealing job, and R50 in the attic. I'm a big fan of insulation because it's basically fuel you pay for just once. But there's only so much you can do without going nuts, then you need to make sure you have adequate radiation.

Jack Horner's estimates seem a bit high. I would guess around 9-11k BTU/hr would be in the ballpark without knowing the details of the construction and location/orientation.

Options might include panel radiators. I'm currently looking at these: http://www.mysoninc.com/Pages/Radiators/Select.html but so far they have not responded to my email asking for technical install info and I'm not sure there's a local dealer.

 

Jack, thanks for the input (again). I did another heat loss calculation from Heatload.com and got 7249btu with a 9' baseboard recommended. The garage is very well insulated and even in the coldest winter day never gets below 40-45 degrees. This room was planned when the house was built 5 years ago. Looking at the way the coppper pipe is run to this room I CAN move the pipe to allow for up tp 15' of baseboard. Thoughts??
also, what is the best supplier of baseboard units?

 

Hey, if it's 7500 then it's 7500. If you post what you're using as input, I'd be happy to run the numbers as well in a separate heat load program. Still seems low to me for a space that size over unheated space.

I have one room with Slantfin Fineline30. It's fine. No frills, works as advertised. I assume multipak80 would be the same deal, just higher output and heavier gauge material. No real experience with other brands.

There is not a huge downside to having more radiation than needed. If you don't have a thermostat in the room, then close the damper to reduce output. But I can tell you from experience that being under-radiated is a real downer. There are actually ways to exploit over-radiation to increase heating efficiency, but that's more of a whole-house issue and gets into boiler control strategies, etc. Probably not what you want to focus on if you're just finishing out a simple room.

 

If you can get the slantfin easily enough through your supplier, and don't mind the added cost, you should be good to go with the multipak stuff. I think it's available in lengths longer than 8', but then the transportation is more difficult. I usually try to put the splices in the b/b's out of sight if possible. Like on a long exposed wall, if you could do it with 2 five footers... and a splice right in the middle ... I might opt to use a longer piece in the middle, and two shorter ones on either end, or perhaps an 8 and a 2, and put the splice near a corner.

I've got one under-radiated room, and I kick myself in the a$$ every winter for not installing enough. I will probably end up with a kicker under a cabinet (one of these years...)

 

You guys have been a great help. I've decided to install two 5" Slant Fin high output baseboards with a thermostat on a zone by itself. If this does not supply enought heat I'll have to do some re-engineering of the wall and an access door that goes into a storage room behind this bonus room (not really a big deal) move the supply lines and add another 5' baseboard to the two I'm installing now. That would give me 15 feet and keep the room toasty. The storage room behind the bonus room is just over 7' wide and about 22' long. I't was just wasted space over a breezeway, so I put in a floor, insulated the whole area and I'm building some shelves for storage. I plan to put in a hidden access door from a bedroom adjacent to this room. A bookcase/door that will open into this room. (I hope the next person to own this house has some boys, it would make a great hiddden fort.) Sorry, my point is now I plan to run the 10' baseboard in the bonus room and then run the return line thru the wall into this storage room and put a 6' baseboard in there to help keep the temperature reasonable. Overkill, maybe, but it just seemed like a perfect fit. I don't know of any reasons not to do it, any thoughts???

 

Overkill maybe... but think of it this way, running a little heat in there might keep the storage area a bit dryer too... I did the same sorta thing, instead of running a straight pipe through the closets, I put a 1' section of baseboard in each one. might also help to eliminate cold drafts.

Keep the pet hair and dust out of them baseboards and as long as you are confident with your heat loss, you might just make it with 10' . Post back when it gets real cold out and let us know!

 

10 ft of high output is ~8000 BTU/hr. Another 6 ft in the closet adds another 4800 BTU/hr. That's about 13,000 BTU/hr new output. I assume you have the boiler capacity to handle that additional load?

If this is it's own zone, then I also assume you are doing the proper near-boiler piping and zoning (valve or pump) and have made sure you have enough pump (if zone valves) or the right pump (if zoning with circulators) to ensure adequate flow through the system.

 

Xiphias:

[QUOTE: Jack Horner's estimate seems a bit high. QUOTE]

Didn't your folks ever teach you how to be polite in mixed company; or maybe you're just looking for a confrontation.

It's insulting of you to assume no one else knows anything about these issues except you; try spending 35 years out there where the rubber meets the road doing hydronic installations & you might change your mind.

Anyone experienced will tell you the HLC's often don't factor in sub-freezing radiational cold coming into the building from concrete slabs; as a result they get it wrong for above garage units, as well as basement apts, etc.

Another area they flub is in calculating bathroom convector sizing; they rarely take into account the tile & stone hard surfaces & the way people feel much colder immediately after a shower or bath.

 

Jack. My sincere apologies. I certainly did not intend to come across as impolite, and in absolutely no way be confrontational.

That said, this is all a discussion and if we were sitting over beers talking this subject I would have put it to you in much the same way: "That seems a bit high. How did you arrive at that number?" And you might have said something like "In my long experience, there's a radiative cooling aspect to this, and here's how I adjust for it." I would have said "Hey, neat. I hadn't thought about that before" and our discussion continues on.

I will be the first to admit that I'm quite low on the learning curve. Heating issues like this have essentially become a hobby for me over the past 18 months. I have a bit of knowledge and every week I learn more.

I had not considered the radiational cooling from a concrete slab. That's new info to me, very educational, and makes a lot of sense. Thanks for that. I can certainly understand how that might contribute to higher than normal heat losses in a space above.

Since I have a similar situation, and am rethinking my radiation in the rooms over the garage, I should probably post a similar thread. I'd value your input.

 

Xiphias:

My apologies as well.

Disregard my last post; it was the Thanksgiving vino talking; after a re-reading, it, doesn't come across too well.

Truth be told, I find your posts & comments on a wide range of hydronic subjects here great reading, informative; please continue contributing.