Gravity conversion

Layth

Hello. I am a homeowner in Minneapolis with a 1940 original gravity boiler in my basement. When we bought the house in 92 a new addition had been added expanding the kitchen and converting an old porch to a sun room. For heat in the new kitchen and sun room resistance heat was added. what we discovered, ( besides a large electric utility bill ) was the kitchen and sun room were always cold. In 98 I tore the sun room down to the studs, insulated the walls with foam replaced all 7 windows with Andersen 400's, added pex tubing to the floor 13'x12' and connected it to the gravity system with a Taco pump for just the sun room loop, about 250'. I added a switch for the pump so I could manually control when I wanted to heat that room. The last two years I went into the crawl space below our kitchen ( created when the addition was added before we moved in ) and dug around the perimeter footings and insulated all the walls with 4" of foam board and covered the sand floor with poly and 4" of foam over that. The next thing I did was place 6" x 48" extruded 1/16th inch thick aluminum heat transfer plates in the ceiling of the crawl space. because the joists are 16"OC the plates pretty much cover the entire ceiling with two runs of plates in each bay and snapped 1/2" pex ( 250' ) into the plates. I did the same in the rest of the basement that was under the old kitchen, another 200' of pex. Good bye all resistance heating.
Because I am remodeling the basement I will be taking out the old boiler and the 3" supply pipes that hang down from the ceiling and run the entire perimeter of the basement. I got a cupule quotes for this project that included a wall hung mod con, three zones ( one for the radiant heat with a mixing valve ) and a perimeter run of 3/4" pex for the 14 radiators, all home runs for around $$$$$. My wife and I are retired and on a fixed income so this would be a huge stretch for us. My question is I know I can run the pex perimeter myself and build the boiler panel ( pumps, expansion tank, air separator, air vent, mixing valve, boiler feed and back flow preventor etc ) I would then hire to have it all installed pressure tested and set up. Does this sound reasonable? I have other questions but this is my baseline so far. Sorry for the length!

Layth

EBEBRATT-Ed

@Layth

Please remove the pricing on your post as we are not allowed to post pricing for many reasons.

Your plan sounds fine as long as you can find a competent person to do the start up. I don't know how permits are handled in your area so that may be a concern.

Most important is to do an accurate heat loss of the house. Download the Slant Finn app for that.

1. Heat loss
2. size and place heat emitters.
3. determine zones and pipe size based on flow needed. The more emitters you install the lower the water temperature you can run which cost more $$$ to install but saves fuel. Below 130 degrees return water will keep the boiler in condensing mode which is what you want if possible.


There is a lot to know to install a mod con properly:

wiring & controls
gas piping
water make-up and backflow preventer/PRV
expansion tank and pump locations
venting and air intake
startup testing and set up

In addition to the radiation and piping loops

Layth

I have begun to string 3/4" pex around the perimeter of the basement. Four runs for hot and cold for two zones. I am drilling 1 1/8" holes in the center of my 9 1/2" joists spaced 2" apart. Because I have 14 radiators ( These are steel finned and I think they called them convectors back then. ) I would like to combine them by geography to cut down on the number of manifolds and loops to the manifold to lower my costs. I will combine no more than three and mostly two radiators at a time. How should I combine them.
At first I was thinking run hot to the first radiator then run a separate pex from the cold of the 1st rad to the hot of the 2nd rad and then from the cold of the 2nd rad to the main cold pex run.
Then I thought why not just run a tee from the main hot to the hot on the 1st rad and then another tee from the hot main to the cold on the 1st rad then another tee from the main hot to the hot on the 2nd rad and finally a tee from the cold main to the cold of the second rad. Maybe I should just send a diagram. Is this ok to combine radiators like this? It would bring me to four loops for the main floor zone to three for the upstairs zone vs 14 home runs to every radiator. By the way the tee's from the original supply ( 4" ) to the radiators are all 3/4" and I will continue this with pex.

Thanks, Layth

Layth

Follow up. I know I am in for a battle when I try to loosen the old black iron (cast?) fittings. any suggestions on how to handle this?

Layth

Jamie Hall

You will get the most even heating -- and much better control and balancing! -- by piping the radiators in parallel -- that is, each one having its own feed off the hot main, and each one having its own return. That way they will all get equally hot water. If you run them in series (cold of the first to hot of the second and so on) the radiators downstream will get cooler and cooler water, and just won't heat as well. Further, if they are in parallel, you can control them individually -- turning one off or down won't affect (much...) the next one, and so on.

As to getting the black iron apart. Good luck. Sometimes it will relent to two BIG pipe wrenches and two strong people. Sometimes you simply have to get destructive. If the fittings are, in fact, cast, they can sometimes be broken using a sledge with a backup on the other side. Sometimes... well, Sawzall blades aren't all that expensive.

mattmia2

You can tee off the mains and feed radiators individually. You should have some sort of a balancing valve at each convector so you can balance the system. Your mains may need to be more than 3/4" depending on how much heat they need to carry or you may need more than 2. Make sure the pex is oxygen barrier. 3/4" pex varies in actual size by manufacturer and is usually smaller than 3/4" copper so be careful of that when figuring out the required flow.

Removal of the fittings can be done by cutting a slot or 2 nearly to the threads with a grinder or reciprocating saw and splitting it with a cold chisel or some fittings can be shattered by hitting them with a pair of hammers, hold one fist maul behind the fitting as a backup and hit the fitting with the other. My wrists would go the grinder or saw route.

hot_rod

Do you know what the heat load is for the home?
You have two 3/4” loops for the 14 radiators?

Layth

The last time I had a company come out for a quote the guess was for an 80000 btu boiler. Since then I have replaced almost all the windows with double glazed and I will be adding another 12" of cellulose in the attic this year. As to the supply runs, one hot one cold and double that for a different zone. I am remodeling the basement at the same time so there will be a third zone with pex going down ( another five loops ) but that will be off the mixing valve with its own pump. I plan on assembling my own boiler panel, see attachment I will be adding a third pump to this.
Doing this myself saves over half from purchasing from BlueRidge. I asked Dan the owner if I could copy the image and he was Ok with it. I really would like to use 3/4" Pex for the supply runs because when I replaced all the galvanized water pipes two years ago with pex and a Manabloc distribution system( I use Uponor expansion fittings and it went very quick) I struggled with the 3/4". Just getting it into the elbows was no fun. Can't imagine what 1" would be like. I'm guessing lots of tee's and elbows and my trusty heat gun. I'm at the drilling holes in the joists for the supply runs point so far, so I can still choose the diameter of the pex. I will be using Uponor's manifolds for all the loops. If I have to go the parallel radiators route that's two seven loop manifolds for 14 radiators. That would be the hot water 140 to 160 degrees run, Another 7 loop manifold for the radiant portion 100 degree run. Thank you for all your responses!

Layth

mattmia2

You can probably use half inch or maybe even 3/8 if you home run everything to a manifold.
There are rack type supports for pex that will let you run a bunch of tubes in parallel.


Building a manifold out of copper or iron fittings and valves will cost less than buying a manifold if you have lots of time and less money.

The first step is do your own heat loss, that will tell you how much heat you need from each emitter. From that you can figure out the flow each emitter needs to provide that heat and that will tell you the minimum pipe size.

Layth

Mattmia2, part of the remodel is to get all the pipes out of sight so I will be drilling 1"holes ( 4 ) through my joists to string the pex through. As for manifolds I notice all the ones I see at Supply House have built in flow meters that can be used for balancing. Building my own might be a consideration but where do I get the flow meters? I would need 14 altogether. Plus could I build the manifolds out of Pex? I downloaded a heat loss calculator from US Boiler so I am working on it.

mattmia2

Be careful you look at what the flow meters can measure. There is a minimum and your individual runs may be below that minimum. Flow meters are expensive weather they are built in to a manifold or a standalone fitting. You can probably balance the system without them.

Pex fittings generally are quite a bit more expensive than copper or iron fittings so you could build a manifold out of pex but the cost is likely to be similar to buying one pre-made.

NoelAnderson

Instead of building manifolds with flow meters, why not try replacing your radiators valves with TRVs to control the flow and balance out the system. Then you can use 1/2 pex from the radiators to a simple copper manifold. Also use an Alpha 2 pump to create a simple but very comfortable radiator zone. All the parts are available at supplyhouse.com.

NoelAnderson

After reading over your post again, I see what you are calling radiators is acutely fin tube convectors which would be hard to connect TRVs to. You are also thinking you need less than an 80,000 Btu boiler to run 14 convectors plus a radiant floor zone. How big is your house? It sounds small, which you would want to limit the number of zones so you don't short cycle your boiler. I would personally try to connect some of your convectors in series to minimize piping and cost. In a small house, there will be some balancing of heat moving from one room to another and you can balance convectors using the damper or by covering up the fin with aluminum foil. Remember a 1" pipe can handle 80,000 BTUs and 3/4" can handle 40,000 and you will be dividing this into at least two zones because the radiant floor and convector will have different water temperatures and ramping times. If the 14 convectors were to use the full 80,000 BTUs, that would equal out to about a .5 GPM in each one and as mattmia2 said, you need to be careful what flow meters you use.

Layth

I am still working on my heat loss calculations, ( almost done ) which will give me I assume a much better picture of supply piping size needed. I was looking at uponor manifolds because I am using their tubing and pipe fittings ( expansion type ) but then discovered that uponor makes reasonably priced manifolds with adjustable flow meters, which I will use. I do like the idea of putting some of the radiators in series because they are so close to each other which would reduce the number of loops used at the manifold. Also I will be using the Grundfos Alpha pumps, three of them for three zones. This is a two level colonial with a basement, about 2100 sf. Please be aware that I am only running the pex and connecting the radiators to the supply, connecting to the manifolds and building the boiler panel and creating a path for the condensate drain. also the venting portion for the modcon. The actual boiler setup, pressure testing and balancing will be professionally done, including all gas connections.

Layth

All of my Radiator to supply pipe are 3/4" . So I will be removing ( or trying to remove ) 3/4" pipe from a threaded elbow fitting. My strategy is to cut the pipe away from the supply which will then let me begin the struggle of removal from the threaded fitting. I read from an older thread that the plumber had used an impact tool with a 7/8" bolt extractor to go over the 3/4" pipe ( with a backing wrench applied) to remove the pipe with success. I have a 1/2" drive impact wrench and 28 fittings to get loose. Has anyone else tried this?

mattmia2

If you have the clearance to get in there, a pair of 24" pipe wrenches seated properly should have no problem getting 3/4" nipple out of a fitting on a closed system like a hydronic heating system. I thought you were dealing with something larger. Choose your transition point where you have room to work on it. I recommend aluminum wrenches and an assortment, both 18" and 24" and 2 24" one wya or the other, wither a steel and an aluminum wrench or 2 aluminum wrenches. You can use the 24" to back up the 18" when tightening things. A little 10" or so wrench cna com in handy in tight places as well as a larger pair of channelocks. I have not found a pair of knockoff of channelocks that work properly, all i have tried don't grip properly.

You can also cut the fitting almost to the threads and split it with a chisel but that should be unnecessary with pipe that small especially in a closed system where it shouldn't have corroded much.

Layth

Thanks Mattmia2. The supply pipes start out at 3" ( I think ) and keep getting smaller as they make their way around the perimeter of the basement but all the radiator ( I should say convectors ) runs to the the supply are 3/4" . most of the fittings I want to attach my pex to are inside the floor joists, so I already know a couple of them are going to be a bear to get wrenches on. That's why I was considering the impact wrench. It would allow me to get into very tight spaces. But I think I can get most of the others with wrenches.

retiredguy

I may get a lot of "push-back" on this comment but if I since you and retired as you say like me, I would have a good contractor look at your heating system and fix only the real problems. Replacing everything is going to cost you a lot with no "pay back" ever on your investment. A good working gravity system is a nice way to heat. If you want to get a faster response on temperature control, you could add a small pump to the gravity system. Take the money you save and enjoy life. Take a cruise around the world, or buy a summer home in a warm climate and enjoy the fruits of your labor. Your kids will thank you as mine have.

Layth

No worries retiredguy. I am a pretty limber and healthy 76 year old and I enjoy most of the doing it yourself stuff. But price was definitely a concern here because I already have had two contractors give me quotes that would require a second mortgage! I can do the majority of this for just the cost of components, lets just say the cost of the latetest MacBook Pro or thereabout. Also a lot of my decisions are driven by my basement remodel that would include the removal of the supply and return pipes that hang down 9" from the ceiling. Oh yeah I don't like to travel. On another note, I have finished three heat calcs ( room by room with window measurements) that all say 50000 btu on the high side which kind of surprised me. I think I will spring for a blower door test as well and run it by the contractor I will be using for the final install. My new mantra, keep the brain engaged!

Layth

I have a question about my 82 year old convectors. As long as I am doing home runs to all my convectors should I do a recirculation clean out for each convector or would that be a waste of time? I'm thinking at least a pressure test.

Mike Krall

Hello Layth,

Was wondering where you are in your project... wondering what your decision on the convectors was.

Mike

Layth

Hi Mike. So far I have drilled holes in the floor joists for all the convectors, all home runs. I have managed to remove all the 1/2" feeder pipes from the convectors, ( with the help of an impact wrench with a bolt biter socket ) and fit in brass pex adapters. Thats two fittings for every convector ( fourteen in all ). I have pressure test all convectors with 65 psi of air. I found out I had used non oxygen barrier pex for my two underfloor radiant zones and am know in the process of replacing all my, pex runs. PITA! My plan is two cleanout all the convectors with city water pressure ( 65 psi ) and maybe run some 8 way boiler cleaner through them as well. I ordered my manifolds, two 5 loopers but I am still researching condensing high efficiency wall hung boilers. Thats it for now.

Layth

mattmia2

I would be more conservative with pressure testing those old convectors. Maybe 25 psig or so and let it sit a while. 60 may be more than their rating and may open up leaks that otherwise wouldn't have existed.

Layth

I have already pressure tested with air at 65 to 70psi. No leaks. I left it for 4hrs on each.

Layth

Layth

Next phase. I have cleaned all of my convectors, ( used 65psi city water to clean out sludge and then circulated 8 way boiler cleaner for two hours and then flushed with clean water ) Today I will be putting up 3/4" ply for my mounting wall, ( boiler, boiler panel, manifolds, water heater etc. ) . It's time to chose a boiler. I am thinking of using the Weil-McLain AquaBalance™ AB-80-H heat only no combi unit. Any problems I should know about?
I was also tinkering with the idea of using a condensing Takagi tankless water heater with the models that support radiant heat because they are half the cost of condensing boilers but no outdoor reset. But then I read a thread here that did not like the idea at all! If I did use the Takagi for dedicated heating I would lose all warranty protection. Still replacement parts are halve the cost of any condensing boiler. I thought if I kept up yearly maintenance it might work?

hot_rod

Just say NO to tankless heaters as boilers. Especially in your conversion, the tankless would need a high head circ and that may be an issue for the piping that was intended for low, slow flow.

Although even with a fire tube boiler, you may need a hydraulic sep or P/S piping. A low flow circ for the distribution, whatever the boiler requires for that side. The fire tube design has a minimum flow and the manual usually indicates pump options.

Layth

Thanks Bob. No tankless. I will be using two Grundfos ALPHA2 15-55F circulators, ( 19' head ) one for the convectors and one for the radiant ( three 250' loops ). Ten of the convectors are home runs and the other four are connected in series because they are physically next to each other. All runs are 1/2" Pex. They all will be going though 3 Blue fin manifolds. Two five loop manifolds are for the convectors ( upstairs and downstairs ) and one 7 loop for the radiant loops, Three loops for radiant with four to spare for the basement which is last on my list because after I finish the heating setup I will be able to continue the remodel, wiring, insulation etc.