Combi

Alan (California Radiant) Forbes

Other than Bradford White's CombiCor, are there any tank-type water heaters with an internal heat exchanger for a small radiant zone and DHW?

Tom_133

Alan,

I have had a similar question, and between that and any good noncondensing wall hungs available? I get nowhere.

hot_rod

Rinnai has been promoting wall hung non condensing models. Are they just tankless DHW or combis?

HTP had an offering of coil in tank models for both in and output.

The Polaris was an inexpensive condenser tank, slap a FPHX on it for hydronics.

Really any tank with one of these HX modules would be a custom option. There are some options to having the HX external to the tank, sizing, repairs, etc.

I'd like to get my hands on one of these Rinnai RHS to experiment with. An 80 gallon tank would make for a sweet hydronic heater.

Seems they could add a top coil easily? Or the external HX module.

Tom_133

Similar to Alan, I have 34 apartments with OLD Baxi's in them, they are combi's. They are very limited on space and money. I know these water heaters with 35K btu's would work great, but they are not super price friendly. I guess a plate would work with a couple pumps on a gas fired, direct vent, but its getting pricey. Htp is nice but also too many dollars.

kcopp

Limited space...how limited? I just ran into a situation where I had to replace a Heatmaker and I opted to go w/ an IBC wall hung and got a Brad-White 30 gallon indirect under it. I suppose you could opt to use a 20 gallon Superstor w/ a mix valve on it.

Tom_133

Kcopp,

I mean no space, and no way to drain condensate, without massive remodeling. Hoping for a tank style direct vent with coil like that bradford white, but those babies are pricey

hot_rod

They don't exist probably because there is little market for them. Could be manufacturers tend to put a high price on small, unique run products if they do build them.

Rinnai has a few models of non-condensing wall mounts. Must be some way to morph them into a combi? Or add a plate HX for the heating side?

Le John

There is the Utica CUB or the Dunkirk DWB that’s a non condensing Combi

Zman

I really feel that as an industry heating was originally very complex compared to other technologies of the time. The old steam systems, particularly 2 pipe and vacuum systems still confuse most techs today.

Over the years, the industry has been dummied down and efficiency has been lost. People stopped using math and began grossly oversizing boilers and circulators.

Sure the new boilers occasionally have issues with gremlins, but compared to the computers we are using and the cars we are driving, they are pretty darn simple.

TAG

Funny -- was just looking at these. Have used these twice ... once for a kitchen floor and another for steam shower walls and towel warmers in the baths.

I no longer own either house -- but, did sell the one with the kitchen floor heat to a friend who is now concerned about the units age .... early 2000's. BW seems to be the only maker .. as was the case years ago.

They also don't seem to make as many sizes ...thought I used the 50g ... they only make a 42 and 70 something now in both single and double wall. I used the single ..

It was just the ticket for both projects -- simple tank and flue .. gave me the small amount of radiant I needed.

Tom_133

Hotrod, I think the issue with a Rinnai is water temp, this place needs 180 at design and no less than 150 most of the winter. Rinnai's for the most part stop at 140, correct?

motoguy128

They do make condensate pumps. No possible way to route pvc tubing to a drain?

DZoro

I have done a basic water heater with side taps to a plate H/E for the radiant. For duplexes that had comi-cores. Just up sized the water heater burners to handle the loads. Good option with limited venting options, and mostly budget.
D

hot_rod

Tom_133 said:

Hotrod, I think the issue with a Rinnai is water temp, this place needs 180 at design and no less than 150 most of the winter. Rinnai's for the most part stop at 140, correct?

That could be, sometimes the commercial versions go to 180F

TAG

Think there may be some confusion -- I believe the "combi" Alan is speaking of is a regular water heater with an internal heat exchanger for a small amount of radiant. It looks like a regular tank type Bradford White water heater. I think the early ones had a 90k burner

It's had a couple of upgrades.

It would give you around 120 water ...

hot_rod

TAG said:

Think there may be some confusion -- I believe the "combi" Alan is speaking of is a regular water heater with an internal heat exchanger for a small amount of radiant. It looks like a regular tank type Bradford White water heater. I think the early ones had a 90k burner

It's had a couple of upgrades.

It would give you around 120 water ...

Makes me wonder what the definition of a combi is. I think it could be a tank with a coil for the radiant, a tankless with a HX for radiant or really any combination?

The EK boilers come with a DHW option with a plate HX and storage tank, I suppose that could be a combi also?

So any dual purpose device where the potable and heating are separate.

Alan (California Radiant) Forbes

TAG said:

Think there may be some confusion -- I believe the "combi" Alan is speaking of is a regular water heater with an internal heat exchanger for a small amount of radiant. It looks like a regular tank type Bradford White water heater. I think the early ones had a 90k burner

It's had a couple of upgrades.

It would give you around 120 water ...

Yes, those old CombiCor's were great except for the heat exchangers that failed after only a few years.

This particular job that I'm looking at has an open system: a tank-type water heater serving DHW and radiant; no separation.

The water heater enclosure is small and there's only a 1/2" gas line. The best bet is a Taco X-Pump Block, but like others have said, it's quite expensive.

I would think that a product like the CombiCor would be very popular, especially in large cities where housing is getting smaller and smaller. Around here, jurisdictions have promoted alternative dwelling unit construction, typically under 1,000 square feet and a tank-style combi unit would be ideal.

TAG

Alan -- I'm reading about all the failures !!

Guess I was lucky !! I'm going to tell my friend to replace. I think they came with a 10 year warranty .. they were not cheap.

hot_rod

Does BW not longer offer the Combi2, they are still on the website.

The Combi 2 had this HX, 1-1/2" tube, glass coated. Same coil we use for the upper in out solar tanks. It should outlast the tank.

motoguy128

> @hot_rod said:
> (Quote)
> That could be, sometimes the commercial versions go to 180F

Outlet temp might go to 180f. But some are limited to as low as 120f on return depending on flow rate. I know Navien water heaters need return water below 110f. It’s not published. But tech support confirmed it when trying to use one as a booster in a kitchen application where the unit was far away from the Main DHW supply in a large community college and the recirc didn’t work to that building. Had to install a mixing valve on the inlet and it worked fine.

hot_rod

motoguy128 said:

> @hot_rod said:

> (Quote)

> That could be, sometimes the commercial versions go to 180F



Outlet temp might go to 180f. But some are limited to as low as 120f on return depending on flow rate. I know Navien water heaters need return water below 110f. It’s not published. But tech support confirmed it when trying to use one as a booster in a kitchen application where the unit was far away from the Main DHW supply in a large community college and the recirc didn’t work to that building. Had to install a mixing valve on the inlet and it worked fine.

Good point, I don't have much experience with the different operating conditions.

I suppose the non condensing versions would control and operate differently, not needing condensing return temperatures?