Gravity hot water system--what do about a new addition? help.....!

islandhome

We have a 3 story 1880s house in New England with a lovely old gravity hot water system. All is well. For now.

But...we are about to embark on a renovation that will enlarge the kitchen from 12 x 18' ---to---> 17 x 23' AND add a mudroom/back entry that will be 120 square feet. We will be enhancing the insulation from pretty much non existent (back plastered walls) up to code and adding a few windows, though all the windows will be energy efficient.

The current kitchen has two radiators. The larger of the two we hope to simply move. The small radiator we would like to exchange for a different shaped radiator to fit under a banquette (I think the new-to-us squat radiator is actually bigger/will do more radiating but I admit I have not figured out how to calculate this).

Questions:
1. Can we just switch out one radiator for a larger one with the same basic piping and expect it all to continue working or is that hopelessly naive?

2. Are two radiators enough (bigger one will be just where the mudroom enters the kitchen, new to us squat radiator on same side in the eating area leaving the other side of the room without a radiator)? ie might the improved insulation offset the larger square footage? how do I calculate that?

3. Should I add a third radiator? Which is to say, can I just add additional first floor radiators without creating a problem?

4. Do I need to "zone this area"? nothing in our house is zoned. We just turn down the 3rd floor radiators to ensure it is not too hot upstairs and it all works pretty well.

Advice appreciated before we believe the first plumber who has a plan, whether or not he has sufficient experience to make this work.

JUGHNE

Your new addition will most likely have a better thermal envelope than the rest of the house.....you will be losing at least one low R-value wall and maybe a window or two.

What do you have for a boiler now? I assume you have no pumps at all?? Some old gravity systems had sloping pipe to aid the flow of hot upward and the return of cool water downward.
With the added length you may run out of that slope.
I am not sure how important the slope upward was to ensure the gravity flow.....just the water cooling in the radiator would create some flow. The upper floors for sure had gravity working in its favor.

A pump could be added to your system by someone who knows what he/she is doing. It actually involves reducing the piping size at the boiler when a pump is added. You could zone your new addition as the heating requirements would be less with new construction than with existing. IMO

Ironman

It will take a lot more info to properly answer your questions. Anything that's done to the piping must be done in the same manner that the system is currently piped. There were different ways that gravity flow systems were piped and knowing that will be necessary. Posting good pics of the boiler and piping is always helpful.

A load calculation needs to be done to determine how much heat the new rooms will need. Square footage is not sufficient.

I would not normally recommend trying to zone a gravity system.

The best thing would be to get a true hydronics pro on site to evaluate what can and should be done. Check the contractor locator on this site.

islandhome

Thanks. Photo of boiler and radiators attached.

Diameter of pipes going into and out of current radiators = 1.5 inches

Big radiator = 26 H x 6 W x 46" long
Smaller radiator = 20.5 x 3.25 x 40" long

Radiator we would like to use = 12 x 12 x 44" long

Kitchen currently has three external walls so a lot of heat loss. The thermal envelope should improve significantly.

Please let me know if there is any other information that would be helpful. We will definitely look up the plumbing contractors on this website--we have consulted with several plumbers to date and received highly contradictory information.

thanks again

Ironman

Can you post some more pics of the near boiler piping from behind the boiler? Also, a pic of the fittings on the main lines where the risers to the radiators connect?

Is there a circulator on the back of the boiler?

You can go to SlanFin's website and download a free heat loss calculator there. Do the entire house envelope and then do the kitchen as it is now and what it will be like after the renovations to see if there's much difference.

A cautionary note:
Any modifications done to the piping MUST be done in the same manner and using the same sizing technique as the original if this is still gravity.

I'm gonna try to attach a radiation table which is used to determine the output of radiators (EDR) based on their square footage. With that, and an accurate load calc, we can determine what size radiation is needed.

Your rads are probably over-sized (which is fine), but any new radiation MUST be proportionately sized with existing for balanced heating. In other words, if the calculations show that your present radiation is over-sized by 25%, then the new radiation should be over-sized by that amount also.

http://www.uticaboilers.com/sites/default/files/293.pdf

islandhome

Big radiator : 68 sq ft
Small radiator : 22 sq ft
"New" squat radiator : 45 sq ft per table provided in link

No circulator
Photos attached. Hope they are useful. Big radiator comes off boiler (I think) and small seems to come off from tubing from a second floor radiator (but I am new to this).

islandhome

SlantFin has a free iphone app!

This is just for the kitchen:

Heat loss current kitchen =6945
Heat loss new kitchen = 8627 (ie 1.24 x higher)

Current radiators: 68 + 22 = 90 sq ft of radiation
If we can fit all 3 radiators in kitchen (not sure where third one would fit) = 68 + 22 + 45 + 1.13 (ie 1.25 x current radiation)

So very simplistically the increase in kitchen size is incrementally balanced by the addition of the new squat radiator. But this does not take the mudroom into consideration (where I was planning on putting the big radiator). And I don't have wall space for the second radiator on the current plan.

The issue is that I don't think I have anywhere to fit 3 radiators into the space.

Yes--we briefly fantasized about radiant floor heat but hydro is too expensive to install and electric would be too expensive to run (though we might consider it for the mudroom, used sparingly).

Stuck!

Larry Weingarten

Hello: I see higher heat loss for the new kitchen than the old, and yes, it's bigger, but did you take into account the insulation, air sealing, and better windows? I'd have expected the heat loss to be less from a well insulated/sealed kitchen. That would be good!

Yours, Larry

islandhome

Hi Larry,

I used the SlantFin app which calculates load after taking into account size, exterior walls, insulation, windows, doors etc.

The new space is 1.8 x the size of the current space. The heat loss calculation suggests that the heat loss will be 1.24x higher so there is definitely a benefit to the insulation, but not only are we increasing square footage but we adding additional windows and a set of French doors.

Larry Weingarten

Hello: Thinking "whole house" it would be interesting to run the calculator for the entire house, with and without insulation. I think you said you planned on insulating everything, so it seems your boiler is likely to be oversized for the "new" house.

You might consider adding a layer of foam insulation outside the studs of the new kitchen. Seems you could reduce the load enough to eliminate the need for another radiator.

Another thing to look at is testing the home with a blower door. This is a diagnostic tool for measuring and finding air leaks. It's probably the single most important thing you can do to reduce the heating/cooling load.... more even than insulation, and it needs to be sealed up before the insulation is put in.

Yours, Larry

islandhome

We'll heavily insulate the exterior walls of the kitchen...but not the whole house. Blower test--yes--that is something we want to do

JUGHNE

Will new addition have basement or crawl space?
The foundation walls/rim joists/seal plates can be a major air infiltration point often over looked in new & old construction.

islandhome

Both....a 6 x 18 foot span will be over a crawl space and the rest will be over a basement. Architect assures me that there is no benefit of foundation over insulated crawl space for the 6' span. .

We do currently have some big leaks along a sill far as we can tell that will be resolved. But right now the kitchen is arctic so that is not a good basis for assessing.