Navien Ch 240 NG question

[Landcrabmech]

First off, I am a multi certified trades-person in Canada (4 Red Seal) designations. Plumbing is NOT one of them, hence I am here to ask a couple questions to the knowledgeable plumbers on here.

I am removing my HW tank and Mini Super Hot boiler and replacing with a Navien CH240. I have 2 zones in my home, 1 upstairs and 1 main floor of radiant floor heating. Both floors are approx 600sqft.

Question 1- Do I need a Navien manifold for the floor heat?
Question 2- Can I just have the internal pump supply the water to the floor heating loops or do I need a separate external pump?
Question 3- Relates to question 2, I have 1 thermostat down stairs and 1 upstairs to control temperatures. So I guess my question is if Zone 1 upstairs calls for heat, will the Navien kick on to supply heat to the upstairs floor? And same for downstairs.

I have 2 thermostatically controlled valves with the SuperHot boiler, so I kind of want the same set up.

One reason I am installing myself is that the first plumbing company quoted almost $10,000.00 for the install and now the second has quoted 45-5500.00. Seems quite high since I already Own the Navien, Have it hung where I want it, Have the intake and exhaust pipes already run and hooked to the unit. All that needs to be done is to hook up the floor heat part of the process and the DHW part of the process. The NG is already in the room where the boiler is so there is no modifications needed to the 1/2" gas piping. I will be using "Gastight" hose to run from the gas valve to the unit.

I have installed and am certified to hook up natural gas and do natural gas conversions on vehicles and I know the household is very similar.

Cheers and thanks in advance for any advice you might share.
If you post negative things about what I am doing, that is your own prerogative. I will not judge you.

Thank again.

Scott
Vancouver Canada

 

[Landcrabmech]

Sorry, couple more things:

Do I need an accumulator (red pressure tank) for the Navien? Currently mine is on the cold water inlet between the fill valve and the boiler so the pipes to it get quite warm, and is charged at 12psi and has a working pressure of up to 70psi. the fill valve is set between 10 and 20psi. My SuperHot MiniGas boiler has an optional circulation pump attached to the side since it does not have an internal pump.

 

[Sponsor]

 

[Plumber69]

did you use the grey exhaust pipe

 

[Dana]

First off, I am a multi certified trades-person in Canada (4 Red Seal) designations. Plumbing is NOT one of them, hence I am here to ask a couple questions to the knowledgeable plumbers on here.

I am removing my HW tank and Mini Super Hot boiler and replacing with a Navien CH240. I have 2 zones in my home, 1 upstairs and 1 main floor of radiant floor heating. Both floors are approx 600sqft.

Question 1- Do I need a Navien manifold for the floor heat?

If not Navien's manifold, it will need some other type of hydraulic separator.

Question 2- Can I just have the internal pump supply the water to the floor heating loops or do I need a separate external pump?

It's unlikely that the internal pump would be able to provide sufficient flow to the zone radiation- it's designed to work for the primary side of the hydraulic separator over a limited length of plumbing.

Question 3- Relates to question 2, I have 1 thermostat down stairs and 1 upstairs to control temperatures. So I guess my question is if Zone 1 upstairs calls for heat, will the Navien kick on to supply heat to the upstairs floor? And same for downstairs.

I have 2 thermostatically controlled valves with the SuperHot boiler, so I kind of want the same set up.

Get at zone controller for the zone valves. The zone controller will call the boiler when either or both of the zone thermostats are calling for heat.

One reason I am installing myself is that the first plumbing company quoted almost $10,000.00 for the install and now the second has quoted 45-5500.00. Seems quite high since I already Own the Navien, Have it hung where I want it, Have the intake and exhaust pipes already run and hooked to the unit. All that needs to be done is to hook up the floor heat part of the process and the DHW part of the process. The NG is already in the room where the boiler is so there is no modifications needed to the 1/2" gas piping. I will be using "Gastight" hose to run from the gas valve to the unit.

CDN$4500-$5500 seems only slightly high, if there is any system design issues to work around (and there are). CDN$10K feels like a gouge.

The design heat load of a stacked pair of 600' over 600' heating zones is probably less than the MINIMUM ~19,000 BTU/hr output of the CH240 at condensing temps and it may need some thermal mass (such as a thermally massive hydraulic separator) to keep it from short-cycling itself into low efficiency and an early grave. It's too much boiler. Since you have a heating history on the place, run this napkin math on wintertime-only gas bills to estimate the design heat load.

19,000 BTU/hr divided by 600' is 32 BTU/hr per square foot. The floor temp would need to be a smoking hot 8-9C warmer than the room temp for the floor to actually emit that much heat, even if none of that 600' was obstructed by cabinets or furniture. If it can't emit the full minimum output of the boiler, the boiler is going to cycle on/off (a lot) during a continuous call for heat, unless there is sufficient thermal mass in the system to establish a reasonable minimum burn time. Every burn cycle throws away some heat during the flue purge by blowing air through the already hot heat exchanger, and there is some unburned gas lost during every igntion cycle. If the minimum burn times can be raised to at least 3 minutes by adding a high volume hydraulic separator, with fewer than 10 burns per hour at 3+ minutes each it'll still do OK on efficiency, but it does wear out the boiler.