Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The TFTN340 and TFTN399 are the two largest TFTN wall models and share everything but depth and ceiling: both are rated 95.4% thermal efficiency, weigh 250 lb with water, measure 25 1/4 by 36 1/2 inches, use 1 1/2" NPT connections and 4" venting. The 399 fires to 399 MBH and is 2 3/8 inches deeper.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | NTI Trinity TFTN340 | NTI Trinity TFTN399 |
|---|---|---|
| Input, minimum | 39.9 MBH | 39.9 MBH |
| Input, maximum | 340 MBH | 399 MBH |
| Weight | 250 lb | 250 lb |
| Width | 25.25 in | 25.25 in |
| Height | 36.5 in | 36.5 in |
| Depth | 18.875 in | 21.25 in |
| Max. equivalent vent length | 150 ft | 150 ft |
| CH water connections | 1 1/2" NPT | 1 1/2" NPT |
| Gas connection | 3/4" NPT | 3/4" NPT |
| Domestic hot water | Heating-only; pair with an indirect tank or separate water heater | Heating-only; pair with an indirect tank or separate water heater |
NTI publishes the 340 at 39.9 to 340 MBH and the 399 at 39.9 to 399 MBH — the same 39.9 MBH minimum fire and the same 95.4% thermal-efficiency rating. Both weigh 250 lb with water, measure 25 1/4 inches wide and 36 1/2 inches high, and connect on 1 1/2" NPT CH pipe with 4" venting to 150 ft per side.
The only physical difference NTI's table shows is depth: 18 7/8 inches for the 340 against 21 1/4 inches for the 399, which houses the larger input. Both minimum fires are identical at 39.9 MBH, so the 399 costs nothing in low-fire behaviour over the 340.
Both are heating-only wall models at the top of the TFTN wall range. The 399 earns its extra 59 MBH of ceiling when the heat-loss or plant-demand calculation approaches 399 MBH; below that the 340 delivers the same low-fire behaviour, weight and venting at a smaller input.
NTI Boilers
The NTI Trinity TFTN340 is the first of the two largest TFTN wall models: 39.9 to 340 MBH input, rated 95.4% thermal efficiency rather than AFUE, at 250 lb with water in a 25 1/4 inch-wide cabinet with 4" venting to 150 ft.
NTI Boilers
The NTI Trinity TFTN399 is the largest TFTN wall model: 39.9 to 399 MBH input at 95.4% thermal efficiency, 250 lb with water, on 1 1/2" NPT CH connections with 4" venting to 150 ft — the wall-hung option NTI positions against its floor-mounted 500–850 sizes.
Almost. Both are 25 1/4 inches wide and 36 1/2 inches high at 250 lb with water; the 399 is 21 1/4 inches deep against the 340's 18 7/8 inches.
Yes — both fire down to 39.9 MBH, so the 399's extra ceiling comes without raising the low-fire floor.
When the calculated load or plant demand exceeds 340 MBH. With identical low-fire behaviour, the only reasons not to choose the 399 are its 2 3/8 inches of extra depth and the capacity you would not use.
A consultation includes a heat-loss review so the size is right the first time.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.