Sizing of a radiator for a bath remodel

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Old 05-05-16, 01:49 PM
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Sizing of a radiator for a bath remodel

WE're in a pissing match with the contractor on a bathroom remodel. can you take a shot at this?

Trying to see how much radiator we need in the bathroom.

We’re getting our bathroom redone. The room is 10’x8’
Ceiling has at least r30 in the attic above
3 ¾ of the walls are interior. No more than ¼ of one of the 10' walls is an outer wall. There’s fiberglass insulation in all the walls including the ¼ of 1 wall that’s an exterior (what fits in 2x4 spaces? R11)

Care to very rough ballpark the amount of radiator for a hot water heating system as a minimum / maximum?

Some background / rant:

There was a radiator heating the toilet / shower area (4' x 8') which was seperate from the sink area (6x8). we made it a single area and talked of making the radiator longer.

The plumber didn't make the changes for the longer radiator before the plywood went down, now he's saying you don't need the longer length. we insisted so he ran the long radiator, andName:  2016-05-05 15.46.18.jpg
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Old 05-05-16, 02:25 PM
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Who designed the remodel & who coordinated the contractors? It sounds like poor planning to me. Except for the chip in the tile, it looks okay.
 
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Old 05-05-16, 02:48 PM
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I cant see the whole baseboard from your pics..

How many ft of element in total? Thats the finned part under the covers...

10x8 = 80 sq ft.
80 x 25 btu = 2000 btu average insulation
80x15 btu = 1200 btu well insulated newer homes.

Looks like slant fin 30 there.. Even if base 1200 the ratings are 600 btu per ft @ 180f boiler temp.

So...

2000btu/600btu = 3.3 ft of baseboard element
2000/600 = 2 ft of baseboard element

http://www.slantfin.com/wp-content/u...30-Ratings.pdf

Looks like an ok job to me...

Instead of the escutcheon I may fill with grout.. But it dont look too bad if your fixtures are oiled bronze...
 
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Old 05-05-16, 02:54 PM
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They also make high output stuff.. 840 btus per ft...

The covers are taller... I put this in when there is not enough wall space for convention length baseboard to heat the room from the load calculation...



http://www.slantfin.com/wp-content/u...80-Ratings.pdf
 
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Old 05-05-16, 08:03 PM
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lawrosa: I spoke to slant fin and the tech said their multi 80 is 730btu? your number is higher? but thanks to your link, I see there's loads of variables? Part of the choices is tied to the flow rate? see the picture of the pump. Doesn't have a flow rate. would you know what it would be?

The original radiator was 3' 3" foot long. It was in an area of 4x8 that only had the toilet and shower and we didn't have any complaints of too hot / too cold.

the area is now 8x 10. your math below - you are saying the 8x10 area only needs 2 to 3.3 feet?! Again, based on the numbers I told slant fin, they said I'd need something a little over 4' (of fineline 30).

Right now, there's 5' 6" of radiator (fin area is 47" (lots of pipe with no fins).



Also, this:

Baseboard Calculator - SupplyHouse.com

says we need 5 feet of fineline 30 or 4 feet of multi 80. more than your numbers and more than we have if we try to put in a radiator using the same end points as before (3' 3")

2 issues:

1) I'd like to know how much radiator I need for the 8 x10 room. Just my thinking - if 3'3" previously wasn't overly hot / cold and you more than double the room space, you need more radiator?

2) My wife especially, is upset after spending all this money on this room, has a pipe coming out of the floor in the middle of a radiator run. This started when the plumber said he was going to put in a longer radiator / we woudl be without heat for a couple weeks on the 2nd floor but 1st floor would keep us warm now in late spring (yeah, I realize now, he could have temp connected the radiator once he moved the stub to accomodate the new radiator to be put in after plywood / tiling.). THen either he forgot / didn't wnat to bother or something, but as carpenter was putting down plywood with old radiator still in place, he came to me and said 'oh, you don't need a longer radiator'. me insisting on that, he says he'd give us the longer radiator and loop back to the existing stub. I don't have the people skills to know how to say 'No, do it the right way' without going overboard / having them just leave (shame on me?). now he's defending the pipe in the middle of the run with 'you don't need the longer radiator', disregarding how it looks like he screwed up / didn't want to move the stub coming out of floor early.

Yeah, I thought about a higher output radiator and called slant fin but they had the 730 btu number which for 3' doesn't give us as much heat as we'd have now?

I thought about lowering / get a wider front to the radiator but that would block the flow of air along the bottom and slant fin says they don't have that.

Also am thinking - put 2 radiator end caps over that (so it looks like 2 radiators next to each other so we get something to cover the pipe / hole in tile? something like this:Name:  s-l225[1].jpg
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Old 05-05-16, 08:06 PM
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here's the pump. I google that model - 007-F4 and don't find anything? and for the f5, the chart shows head vs. flow rate. Am I wrong? some pumps run at a set flow rate? how do you tell what the system flow rate is now, short of putting a flow meter in line?

thanks!
 
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Old 05-06-16, 04:01 AM
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Your fine.. your over thinking this... The slant fin charts are accurate so not sure what slant fin is telling you.. With that pump most likely your getting 5 GPM..

Remove the extention and covers and install the multipack.. with the H1 element..

2000/840 =2.3 ft..

Since without the ext you have 3.3 ft youll be overratiated for that room.. Youll have plenty of heat..

Youd also be fine with the standard 30 baseboard..

2000/600 = 3.33

The rough estimate of heat loss I gave you is pretty accurate.. I been doing this 30 plus years..


10x8 = 80 sq ft.
80 x 25 btu = 2000 btu average insulation
80x15 btu = 1200 btu well insulated newer homes.

If the home is real drafty I use 35 as the x number......

Anyway you look at it on average a 10x8 room needs 2000 btu of radiation..


Example ... How many sq ft is your home?

Say its 1500 sq ft.. 1500x25 = 37500 btu... Now go add up all your baseboard in the whole home. I bet youl be close to your #..

Let us know...
 
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Old 05-06-16, 06:15 AM
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law: thanks for the info, but part of this that (we don't feel) is overthinking is that there's this pipe in the middle of the radiator run.

you're saying with the multi 80 (and h1 element?) between the wall and existing pipe going into floor (3'3"), we'll have enough heat!?

But again, the 3'3" run was giving off the 'correct' amount of heat for years in an area that was 4x8. that and your recommendation that we can use those same end points with a beefier unit (the multi 80) and it'll work just seems (to an OCD / compulsive) to not jive? the multi 80 isn't going to give off more than double the old radiator's heat? is it?

(am I wrong? if the room more than doubles square footage (from 4x8 to 10x8), you need (more than) double the heat going into the room? the volume of air to heat increases by that same factor? most all of the walls are interior before and after (yeah, what do you think of the kraft paper insulation on an inside wall? I questioned it and he said the paper is not stapled in place so moisture isn't an issue) How much babysitting / questioning should you have to do for a contractor

heres a picture of the old radiator - its not like it has only 2" of fins.
 
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Old 05-06-16, 12:22 PM
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you're saying with the multi 80 (and h1 element?) between the wall and existing pipe going into floor (3'3"), we'll have enough heat!?
Yes with that size room and the multipack with H1 element you only need 2.3 ft.. But put 3.3 ft of multipack and you'll have an extra ft of radiation...

But again, the 3'3" run was giving off the 'correct' amount of heat for years in an area that was 4x8. that and your recommendation that we can use those same end points with a beefier unit (the multi 80) and it'll work just seems (to an OCD / compulsive) to not jive? the multi 80 isn't going to give off more than double the old radiator's heat? is it?
Yes 3.3 ft of your old baseboard was giving 1800 btu of heat.
3.3 of the multi pack will give of 2520 btu of heat.

This all according to a 10x8 room.. (2000 btus)

A 4x8 room is 32 sq ft and requires only 800 btus...
 
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Old 05-06-16, 12:45 PM
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Again, thanks for all your time with this and with everyone else you help here : )

And I really don't mean to belabor all this, but....

any thoughts on why that 4x8 room with about 3' of fins wasn't sweltering? your saying the 4x8 room needed just 800 BTUs but the 3' or so of fins was putting 1800 / 3.3 * 3' = about 1600 BTUs into the room - it would seem to be way more than needed... but we never thought it was hot / cold before. That's why keeping the same length radiator in a room that is more than 2x as large just seems too hard to grasp.

We have the wall and the pipe coming out of the floor is 3.3' from it. There needs to be some bare pipe for connections, etc... So when you say: '3.3 of the multi pack will give of 2520 btu of heat.', is that a measure of the wall to the outside of the end cap of the covering? or 3.3' of finned area? I'm thinking you mean the latter : ( and it's not really 3.3 feet, it's 3'3" or 3.25. Take out the bare pipe length needed for connections and the finned area drops more. Still going to be more than 2.3 you say wee need, but...

OH! Another question - this radiator will be right next to the toilet - it'd be running along your left side as you still on the toilet. I like to read in there : ) is that concentrated heat of the multi 80 too much to sit next to? Figuring where to put the toilet paper holder, I measured 7" from outer part of my thigh to the wall when sitting on the toilet.
 
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Old 05-06-16, 01:11 PM
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Many reasons... Bent and dusty fins on the baseboard = less heat output..

Boiler not really reaching 180f too.. Maybe you have a nod con boiler or the actual boiler temp is set lower then the average 180f.

Or that baseboard may be last on the line/loop.. 180 boiler temps out but that last baseboard only receives 160f temps..

When I size a home for baseboard I take the last on the line into account and over size often..

So a room that needs 1 ft of baseboard @ 180f I will calculate it for 160f.

So at 160f = 480 btu per ft



or 3.3' of finned area?
Finned area...

OH! Another question - this radiator will be right next to the toilet - it'd be running along your left side as you still on the toilet. I like to read in there : ) is that concentrated heat of the multi 80 too much to sit next to?
IDK.. Im only giving you that calculations...

If it were my home I calculate lower on baseboard and use 550btu per ft.. If I had a 10x8 bath I would want 4 ft of baseboard in there at least to accommodate the 2000 btu I need for a room of that size..

Its hard to say why that baseboard did not overheat the bath.. How was the bath expanded?
 

Last edited by lawrosa; 05-06-16 at 04:26 PM. Reason: spelling
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Old 05-06-16, 02:20 PM
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(am I wrong? if the room more than doubles square footage (from 4x8 to 10x8), you need (more than) double the heat going into the room? the volume of air to heat increases by that same factor? most all of the walls are interior before and after (yeah, what do you think of the kraft paper insulation on an inside wall?
Yes, you are wrong. The heat loss is primarily through the outside wall and also the ceiling. Doubling the area does NOT double the required heat input. In the first post you stated that no more than 1/4 of the ten foot wall was outside wall, which would mean about 2-1/2 feet of outside wall.

Mike has given you excellent advice, I suggest that you follow that advice.

The Kraft paper on the inside wall insulation is not necessary but neither will it harm anything.
 
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Old 05-06-16, 07:57 PM
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Furd hit it right on the head. How much area has been added to the exposed area only. Inside walls, ceiling and floor area does not matter, only exterior exposure or what they call unconditioned space. This is a wall surface not exposed to the outside but an unconditioned room.Is there better insulation?
What part of the country do you live. What temperature do you keep your home.
If you want I will run a quick heat loss for the area at no charge.
PM me if interested.
 
 

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