Which Boiler do I need?

silvermonte · 2026-09-02T11:42:59-0400

Heres the back story, self built place. 80'x50' post frame building, 2500 of it is garage and 1500 of it is house, the place is tall enough for a second floor but for now its just a single floor. The concrete slab is just poured on grade, has r20 pink board insulation all the way around the slab 3' down and r10 under the concrete. The walls are r29 and the attic is r60 and Im located in east central Iowa. The garage has 2 zones and the house has its own zone, id like to plan ahead and have the option for a 4th zone for the second floor when that becomes a reality.

Editing for more information- 1/2" pex and i tried really hard to make all the lines as close to 290', the one that is off the most is just 10' shorter compared to the others. There are 2 zones in the garage with 5 runs apiece, and the house has 5 runs for the 3 zones. If a 4th zone went in for the second floor it would probably only have 4 runs at most. The house has 2 1/2 baths in it.

Heres where I would like some help. Are there better options for the money then the items listed? I have propane and electric is just silly expensive where im at so thats not an option really.

boiler- https://www.menards.com/main/plumbi...ler/rmcbh-l199i/p-1642874299838873-c-8519.htm

https://media.richmondwaterheaters.com/blobazrheem/wp-content/uploads/sites/43/2023/07/T-TK-RMCBH-L-Rev-1-Richmond-Combi-ssindd.pdf

Panels- https://www.menards.com/main/plumbi...ete-system/6959775/p-1471978652594-c-8521.htm

HS1T4ZPMP - 1 Temp, 4 Zone by Pump Zoning Panel

This Zoning Panel works with various Master Panels and is utilized when more than one thermostat zones is required in the system. The Zone Panel extracts the processed heated fluid from the Master Panel and redistributes to each thermostat emitter zone. The emitter circuit has hydraulic...

www.hydro-smart.com

https://www.hydro-smart.com/products/hsps120lt?_pos=1&_psq=hsps&_psid=70f6e9ef1&_ss=e

fitter30 · 2026-09-02T12:46:03-0400

Size of pex ,lenght of loops and number of them. Mernards thinks im a bot.

kj_mustang · 2026-09-02T13:40:26-0400

Boiler spec write up is not very thorough. Since it is a Combi boiler you really need to know the max DHW flow rate and how much DHW flow you and the house occupants potentially will be using at the same time.

Sumboodie · 2026-09-02T13:44:43-0400

Need to do a manual J calc.

Boiler link doesnt work, says I need security.

Sumboodie · 2026-09-02T13:45:30-0400

kj_mustang said:
Boiler spec write up is not very thorough. Since it is a Combi boiler you really need to know the max DHW flow rate and how much DHW flow you and the house occupants potentially will be using at the same time.

And cold water temp.

kj_mustang · 2026-09-02T13:50:10-0400

Found the boiler info on their website. These are made by Rheem. 199,000 BTU model has a 5 gallon a minute DHW flow rate at 67 degree rise.
https://files.myrheem.com/webpartners/ProductDocuments/BB95E591-FC47-408F-921F-62E12F00A4DD.pdf

PoorUB · 2026-09-02T14:11:44-0400

How many feet of tubing? Roughly 30 BTU per foot, so no sense in putting i a larger boiler than the tubing can handle.

Sumboodie said:
Need to do a manual J calc.

Yes and no. The manual J might come out higher than the floor tubing can use. If the building needs 100,000 BTU, but he has only 50,000 BTU of tubing a larger boiler is a waste.

silvermonte · 2026-09-02T14:59:47-0400

PoorUB said:
How many feet of tubing? Roughly 30 BTU per foot, so no sense in putting i a larger boiler than the tubing can handle.

Yes and no. The manual J might come out higher than the floor tubing can use. If the building needs 100,000 BTU, but he has only 50,000 BTU of tubing a larger boiler is a waste.

I have roughly 4350' of 1/2" tubing in the floor between the 3 zones.

silvermonte · 2026-09-02T15:02:15-0400

fitter30 said:
Size of pex ,lenght of loops and number of them. Mernards thinks im a bot.

1/2" pex, roughly 290' apiece and 15 runs total , 2 zones in the garage and one in the house that are 5 runs apiece.

silvermonte · 2026-09-02T15:03:44-0400

kj_mustang said:
Boiler spec write up is not very thorough. Since it is a Combi boiler you really need to know the max DHW flow rate and how much DHW flow you and the house occupants potentially will be using at the same time.

I put a new link up that hopefully helps.

PoorUB · 2026-09-02T15:21:35-0400

silvermonte said:
I have roughly 4350' of 1/2" tubing in the floor between the 3 zones.

4350 feet x 30 BTU gets you 130,000 BTU. So for the existing you need 130,000 BTU. Then add any anticipated additions, or the second floor in your case. Also you 50x80 comes to 4,000 sqft. Most of the time, for floor tubing in normal situations we always ended up with I foot of tubing per 1 sqft of floor, 4250 feet is a bit more, but pretty close to the 1 ft per 1 sqft. So if the anticipated second floor is 1,000 sqft, you will need another 30,000 BTU. In reality you probably don't need that much heat for the space. the 199,000 boiler is not out of line, 150,000 would probably do it.

Are you looking for a combi boiler, for domestic hot water too? If you are then you will want to size it for your domestic hot water requirements.

silvermonte · 2026-09-02T15:57:32-0400

PoorUB said:
Are you looking for a combi boiler, for domestic hot water too? If you are then you will want to size it for your domestic hot water requirements

That particular boiler is a combi boiler, which I wanted for domestic use also, if its feasible. I have room for a standard water heater, but why use one if I can get away with a combi boiler and call it a day. Im out of my element with this stuff which is why Im asking for suggestions. The house would be 2 1/2 bathrooms and a 4 bedroom house. I dont know what a standard amount for domestic water would use.

fitter30 · 2026-09-02T20:07:52-0400

silvermonte said:
1/2" pex, roughly 290' apiece and 15 runs total , 2 zones in the garage and one in the house that are 5 runs apiece.

147,900 btu's total
each zone 49,300 btu's
Flow through each loop 1 gpm
Head .03X300= .9' then add 2' for piping around the boiler.
In the house any wood floor coverings or vinyl check with flooring manufacturer for temp limit for water temp most 80-85°. Boiler glycol 30% minimum 50% max. 30Glycol manufacturers list total freeze protection and slush. Slush might have to go to web site or call customer service.

jlv03 · 2026-09-03T07:59:07-0400

If you have the space in your utility room, I would put some thought into an 80 gallon heat pump water heater (HPWH). Then either skip the combi boiler or use the combi to back up/complement the HPWH.

silvermonte · 2026-09-03T09:13:38-0400

jlv03 said:
If you have the space in your utility room, I would put some thought into an 80 gallon heat pump water heater (HPWH). Then either skip the combi boiler or use the combi to back up/complement the HPWH.

What is the advantage of that heat pump so I can look into them? Im not aware of them.

jlv03 · 2026-09-03T10:17:13-0400

Biggest advantage of the heat pump water heater is low cost to operate. As a side benefit it cools and dehumidifies the space in which it is located.

Sumboodie · 2026-09-03T10:45:17-0400

I have a combi.

You should put a small water heater in line. There's quite a delay between opening a kitchen or bathroom spigot and having hot water. And that happens everytime. Can't close the water and open 30 secs later and expect hot water.
Takes a good 30-45 seconds for it to fire and make hit water and the water pipe to clear. Not quite as bad if it's already heating for the floors.
Even just a under sink 2-3 gallon tank would be fine as a buffer tank.

As far as boiler size, again, DO A MANUAL J. That's the correct way to know.

Sumboodie · 2026-09-03T10:47:51-0400

I

fitter30 said:
147,900 btu's total
each zone 49,300 btu's
Flow through each loop 1 gpm
Head .03X300= .9' then add 2' for piping around the boiler.
In the house any wood floor coverings or vinyl check with flooring manufacturer for temp limit for water temp most 80-85°. Boiler glycol 30% minimum 50% max. 30Glycol manufacturers list total freeze protection and slush. Slush might have to go to web site or call customer service.

If that was true, any house in the south would ruined floors. 80* is a "nice day" haha

danski0224 · 2026-09-03T12:33:40-0400

Sumboodie said:
As far as boiler size, again, DO A MANUAL J. That's the correct way to know.

Should have been done before the tubing was installed...

But, you know.

caleb383 · 2026-09-03T12:33:51-0400

silvermonte said:
Heres the back story, self built place. 80'x50' post frame building, 2500 of it is garage and 1500 of it is house, the place is tall enough for a second floor but for now its just a single floor. The concrete slab is just poured on grade, has r20 pink board insulation all the way around the slab 3' down and r10 under the concrete. The walls are r29 and the attic is r60 and Im located in east central Iowa. The garage has 2 zones and the house has its own zone, id like to plan ahead and have the option for a 4th zone for the second floor when that becomes a reality.

Editing for more information- 1/2" pex and i tried really hard to make all the lines as close to 290', the one that is off the most is just 10' shorter compared to the others. There are 2 zones in the garage with 5 runs apiece, and the house has 5 runs for the 3 zones. If a 4th zone went in for the second floor it would probably only have 4 runs at most. The house has 2 1/2 baths in it.

Heres where I would like some help. Are there better options for the money then the items listed? I have propane and electric is just silly expensive where im at so thats not an option really.

boiler- https://www.menards.com/main/plumbi...ler/rmcbh-l199i/p-1642874299838873-c-8519.htm

https://media.richmondwaterheaters.com/blobazrheem/wp-content/uploads/sites/43/2023/07/T-TK-RMCBH-L-Rev-1-Richmond-Combi-ssindd.pdf

Panels- https://www.menards.com/main/plumbi...ete-system/6959775/p-1471978652594-c-8521.htm

HS1T4ZPMP - 1 Temp, 4 Zone by Pump Zoning Panel

This Zoning Panel works with various Master Panels and is utilized when more than one thermostat zones is required in the system. The Zone Panel extracts the processed heated fluid from the Master Panel and redistributes to each thermostat emitter zone. The emitter circuit has hydraulic...

www.hydro-smart.com

https://www.hydro-smart.com/products/hsps120lt?_pos=1&_psq=hsps&_psid=70f6e9ef1&_ss=e

That is a pretty big space to heat, so zoning it properly from the start is definitely the right move. Skipping electric and propane makes total sense given the local costs, though balancing those long line lengths for the radiant panels will take some careful planning.

Sumboodie · 2026-09-03T12:56:38-0400

danski0224 said:
Should have been done before the tubing was installed...

But, you know.

I doubt mine was.

It's 1250 sq ft on 3 loops. The pex is run with not much planning, least that I can figure. It's not even O2 barrier pex.

It heats though. Got lucky I guess. (I bought it 10 years after built)

silvermonte · 2026-09-03T14:22:27-0400

danski0224 said:
Should have been done before the tubing was installed...

But, you know.

I started looking into that and it was over my head. I just kinda winged it and copied off of videos I watched that had a place that was similar to my place. I learned enough to get the tubing laid out to get them as close to the same length as possible and drew up a few plans until i had it right. Admittedly not the smartest way to do things.

silvermonte · 2026-09-03T14:24:16-0400

caleb383 said:
balancing those long line lengths for the radiant panels will take some careful planning.

my manifolds have a little pressure gauge, or flow gauge of some sort that you adjust for each run to get them all to match

silvermonte · 2026-09-03T14:29:41-0400

jlv03 said:
Biggest advantage of the heat pump water heater is low cost to operate. As a side benefit it cools and dehumidifies the space in which it is located.

I started doing some reading , pretty neat stuff. I pay 27 cents a kw/h so I worry about the running cost of one of them.

Which Boiler do I need?

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