Heated floors

mwags

I'm a big diy guy. I'm really new to hydronic heat. I am completely remodeling a bathroom and would like to add floor heat and eliminate the baseboard heater. What would I need to reduce the temperature for the floor heat? I might do the same for the kitchen next year and run it on the same zone.

Gordy

First thing would be to perform a heatloss calculation for the bathroom, and kitchen. This is to be sure that the btu requirement can be covered by the radiant floor alone. Since you will be removing the baseboard heat.

What type of radiant floor will you be installing?
Suspended tube
Staple up
Sandwich

If your electric rates are not astronomical. An electric Matt system would be a nice floor warming option. They come with timers, and or schedule thermostats. So you can program for mornings etc.

mwags

It's a pretty custom install. Floors have been built up to match the rest of the house. I am planning on sandwiching pex between the subfloor on the joists and the subfloor for the ceramic tile.

Gordy

What you have to be aware of if the bathroom is small is there may not be enough floor space to generate the same output your base board did.

Sandwich is good. With plates is better. 6-8 inches in center better yet.

Ironman

Yes, you would need lower water temp, plus there could be several other considerations that may need to be addressed, not the least of which is that the floor may not produce enough heat for the bathroom.

The key to getting a radiant floor that functions satisfactorily is PROPER design. Usually, just trying to tie in a small bath with a system that has high temp radiation like yours turns out to be disappointing to say the least. Tying it onto the same zone as the kitchen may not be the best route either since your connecting what's usually the coldest room (small bath) with what is the hottest room (the kitchen).

It can be done if you're willing to spend the $$ to do it right. Otherwise, it may be more profitable to use an electric floor grid in the bathroom. This is usually what we end up recommending for an older house with a small to medium size bathroom.

What type of boiler and piping do you have? Pics would help a lot.

SWEI

Given the limited amounts of usable floor space, bathroom floors are almost always a challenge. Radiant walls rock.

mwags

It's a small bathroom. Planning on running lines everywhere except where I need to drill and cut holes. If I insulate all walls (int/ext) would that help with heating?



On another note. How would a bigger boiler affect the systems efficency?

SWEI

mwags said:

It's a small bathroom. Planning on running lines everywhere except where I need to drill and cut holes.

Understood, but by the time you eliminate the floor areas covered by a vanity, a tub/shower, and a toilet there generally isn't a whole lot left. Throw in an exterior wall and a window and you almost always end up with an under-heated room. The answer is more tubing (think walls and/or ceiling) or a different heat source. Electric mats still provide toasty feet when the boiler is shut down for the season.

If I insulate all walls (int/ext) would that help with heating?

I cannot overemphasize the importance of insulating the exterior walls. Interior walls not so much, but sometimes for sound insulation.

How would a bigger boiler affect the systems efficiency?

Bigger than what?

mwags

Old boiler in the house is a dinosaur. I can pick up a 4 year old boiler pretty cheap from a family member who switched to forced air but it's noticeably larger.

Will pex hold up to boiler heat?

Gordy

Here is an example:

6x12 bath is 72 SF.

Deduct 12.5 SF for a 2'6"x5' tub shower.
Deduct 5 SF for a 2'6"X 2' vanity
Deduct 3 SF for toilet.
Deduct 4 SF for a linen closet.

That's 24 SF
That leaves 48 SF of usable radiant floor.

At 30 btus SF output for radiant floor your looking at 1440 btus.

How long is your existing base board, and what type?

Gordy

Your present boiler is most likley already oversized.

A larger boiler does nothing to increase the output of the floor.

Supply water temperature, and flow rates do that. You are limited as far as water temps because of comfort. With a sandwich type, tile floor,and being a bath you could get away with 87 degree floor surface temps. This would increase output slightly too.

Also keep the tubing away from the toilet flange about 6".

mwags

Existing base board is about 4 foot copper tube with fins. The tub is metal and I'm planning on running tubing under that as well. Would that make a difference?

Gordy

Depending on average water temp, and flow rate that 4' baseboard section could be putting out 2000 btus to 3000 btus.

So in my example how would your bath compare in size?

No the tubing under the tub may take the edge off the tub, but do little if anything to heat the bathroom.

mwags

Gordy, I was curious as to how the bigger boiler would affect my operating cost.

Gordy

By no means are we talking you out of a radiant floor. You have to do the math to avoid disappointment. As SWEI pointed out there are other possible radiant surfaces. Depends on extent of renovation.

Towel warmers are very elegant also adding to outputs.

If there are going to be other radiant spaces then a mixing valve at the boiler to service this and future loops is a good option.

Gordy

The bigger boiler will increase your operating cost due to cycling possibly. This pulls efficiency down in the weeds.

I would Highly recommend doing a total room by room heat loss of the whole house before making that jump.

Slant fin offers a free online calculator.

Gordy

We really know nothing of the old dinasour, or the 4 year old boiler at your disposal to make to many assumptions.

Some pics, boiler plate details of gross outputs. Boiler make, and model etc. helps a lot.

mwags

I'm going to turn it into a 3 zone system. The living room, bathroom, and bedrooms are far to warm in the winter with the fireplace going. In this stage it probably would not take much to add heat to the walls. Where can I find a good heat loss calculator?

mwags

I'm not sure if the old boiler could be brought back to safe operating condition or not. It's at least 30 years old. I'll do some research on the other boiler.

Gordy

If you have an iPad slant fin has a heatloss app.

mwags

Newer boiler is a Weil-McLain CGa-5.

Gordy

Cga5 has 117k output.

mwags

Thinking about adding a section of radiant wall behind the back wall of the tub surround. Would the surround for the tub affect the heating properties of the radiant wall?

Gordy

If there is an air space between the surround, and the wall it will reduce output. Most surrounds have depth to them.

If it were cement board, and tile different story. Those are conductive materials that add little r value to the assembly.

Let's not forget about using quality heat transfer plates.

Is the tub against an exterior wall?

mwags

Against an interior wall. Might tile the surround down the road but for now I'm just putting up a glue up surround to get the bathroom useable.

mwags

What heat transfer plates would you recommend?

Gordy

Stamped omega profile. Don't go for the thin gauge lose fitting type.

hot_rod

Is it a cast iron tub? Put the tube against the tub and you have a nice cast iron radiator.

The old rubber tube and construction adhesive worked

Gordy

hot rod said:

Is it a cast iron tub? Put the tube against the tub and you have a nice cast iron radiator.

The old rubber tube and construction adhesive worked

That would be a neat trick with an existing tub in place.

hot_rod

If it is a skirted tub, in place, it would be a tough go.

He mentioned a complete remodel,so maybe a new tub?

I not sure how many cast iron tubs get installed anymore. The homes we worked on usually had the large Kohler drop in cast tubs with a deck built around them.

mwags

Just a stamped steel type tub. Definitely looking into getting a smaller boiler. Any recommendations for a direct vent boiler?

mwags

Trying to size a boiler and I came up with a BTU requirement of 34,485. Does this seem right for a 1000 square foot home?

Gordy

Sounds close for 1k SF.

rick in Alaska

Sounds high to me. I am heating 2400 square feet for around 32000 btu's. ( if memory serves me right). But, I am also heavily insulated and all radiant, so that does factor in.
Rick

Gordy

Find a boiler that small.....

Danny Scully

@gordy, Burnham series 202?