DHW - What is best with Boiler setup

drivenserb

Hi, I’m in the process of replacing my boiler and power vented water heater.

I’ve received 3 quotes I’m being told 3 different things will be the best for my home.

All company’s are quoting me viessman B1HA or B1KA

Option 1 B1HA and for DHW tankless water heater.

Option 2 B1KA only 3.6 GPM

Option 3 B1HA and 42G indirect tank.

I have another guy coming tomorrow to quote me a Navien combi boiler saying he can add a resivoir tank to the combi to bump me to 5GPM but sounds fishy to me and I do not want any pressure issues either.

It’s a 2 story home with basement rental. 2 bath, 2 kitchen 2 Laundry. The problem I’m having is everyone is contradicting each other as to what the best solution is for DHW. From what I’ve read Indirect tank should be the best but is 42G tank really big enough? I’m being told yes but I don’t think it is.

What are disadvantages to going indirect? I do not want to have hot water shortage issues and I can’t rely on what these contractors are telling me.

I’m quoting with very large well known contractors in Toronto, Ontario.

Thank you in advance!

psb75

One thing you didn't mention was "the number of people" living in this dwelling. That would be key info for DHW sizing. Did you provide this info to the folks quoting you?

EzzyT

I would go with the indirect tank option. Tankless and wall hung combi units can’t deliver high gpm demands you’ll definitely see once in awhile and it will be frustrating. Plus the wall hung combi’s most likely on the heating side will be oversized for your home all depending on the Heatloss which is what’s needed to determine what size boiler you’ll need in your home.

Zman

The rental is the great unknown. I would oversize to be sure they don't leave you with cold water.
With option 1, you will likely need 2 units to cover the load. Is your gas piping large enough?
Option 2 will not work, the combi with 150k will not keep up.
I like option 3 but would go with a larger indirect with a mixing valve to maximize storage. 60-80 gal minimum.
Do you have any big tubs or high flow showerheads?

drivenserb

> @psb75 said:
> One thing you didn't mention was "the number of people" living in this dwelling. That would be key info for DHW sizing. Did you provide this info to the folks quoting you?

There will be my family of 3 and possibly 1 tennant since it’s a bachelor apt that’s what I’m aiming for.

Yes I have told them 4 people and they’re aware the basement will be rented.

drivenserb

> @EzzyT said:
> I would go with the indirect tank option. Tankless and wall hung combi units can’t deliver high gpm demands you’ll definitely see once in awhile and it will be frustrating. Plus the wall hung combi’s most likely on the heating side will be oversized for your home all depending on the Heatloss which is what’s needed to determine what size boiler you’ll need in your home.

Thank you I think indirect tank is the winner here but these contractors don’t get it. I now have 2 more contractors telling me to go Navian combi boiler. I won’t have incredible heat loss in the home anymore I’m switching to triple pane windows And doing some insulation around the house. I was previously told I only need 80,000btu to heat my home.

drivenserb

> @Zman said:
> The rental is the great unknown. I would oversize to be sure they don't leave you with cold water.
> With option 1, you will likely need 2 units to cover the load. Is your gas piping large enough?
> Option 2 will not work, the combi with 150k will not keep up.
> I like option 3 but would go with a larger indirect with a mixing valve to maximize storage. 60-80 gal minimum.
> Do you have any big tubs or high flow showerheads?


That’s the thing and these guys don’t seem to understand that it’s an unknown with the rental. I really don’t want to sacrifice pressure or temperature with a combi I think I’m going to have to push for indirect tank and go bigger that 40-42g that I’m being recommended. I do have a very deep tub in my bathroom but it never gets filled. The basement shower however has a rain head and has a waterfall it’s pretty high flow. It’s one of those large units that mounts to the wall so unfortunately I don’t plan on changing it.

drivenserb

Sorry for getting back to everyone so slow but I appreciate all the responses. Your feedback has been helpful!

hot_rod

It always comes down to how much is enough, DHW. I suppose somewhat it depends on who is paying the DHW bill.

I've been on both sides, my opinion is the rental building owner gets to decide how much DHW is available. I've lived with 30 gallon electric tanks in a rental apt with 6 ski bums one winter, we made it work.

Pretty much the rest of the world survives on tankless or combis, very rare to find a tank type DHW source in Europe, maybe some hotels.

If you have 2.5 gpm of continuous DHW available you adjust to that supply. If you give them 80 gallons of tank supplied DHW, guess what

ChrisJ

My sister and her husband just had a Weil Mclain combi installed and their claims are sometimes it's hot and more often than not it's barely warm and they cannot see any reasoning behind it. I.E. it's only one person taking a shower etc.


Their heating guy said it's typical for such a unit to behave this way so now they're planning on using a hybrid tank heater in series with it.


Sadly, that's all I've heard.

icy78

> @ChrisJ said:
> My sister and her husband just had a Weil Mclain combi installed and their claims are sometimes it's hot and more often than not it's barely warm and they cannot see any reasoning behind it. I.E. it's only one person taking a shower etc.
>
>
> Their heating guy said it's typical for such a unit to behave this way so now they're planning on using a hybrid tank heater in series with it.
>
>
> Sadly, that's all I've heard.

Sounds like it's not set up right.
It has to be...too much flow (incorrectly sized), or fuel input too low, (gas line size), or a mixing valve was piped in and is set too cold.
The pitfall of combis is that, to supply "enough" hot water, one often needs twice the btu capacity than is actually needed for the building heating requirements.

ChrisJ

icy78 said:

> @ChrisJ said:

> My sister and her husband just had a Weil Mclain combi installed and their claims are sometimes it's hot and more often than not it's barely warm and they cannot see any reasoning behind it. I.E. it's only one person taking a shower etc.

>

>

> Their heating guy said it's typical for such a unit to behave this way so now they're planning on using a hybrid tank heater in series with it.

>

>

> Sadly, that's all I've heard.



Sounds like it's not set up right.

It has to be...too much flow (incorrectly sized), or fuel input too low, (gas line size), or a mixing valve was piped in and is set too cold.

The pitfall of combis is that, to supply "enough" hot water, one often needs twice the btu capacity than is actually needed for the building heating requirements.

I don't know.
As far as I know, hearing all of this remotely, the mixingvalve is set as high as it can go and the boiler's DHW is set to 131, also maxed out.

It's a WM ab-155c which sure is oversized for the house IMO but doesn't explain the domestic HW issue. A single shower shouldn't overload it sometimes and not others?

You know how it is hearing all of this second hand though.

Perhaps I need to start a thread and get them some help.
I assumed what they were told was the truth "it's just the way it is".

hot_rod

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

ChrisJ

hot_rod said:

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

It's max setting is 131F.
So if that's true, the hottest water you can theoretically get from it is 113F best case scenario?

How is that practical!?

hot_rod

ChrisJ said:

hot_rod said:

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

It's max setting is 131F.
So if that's true, the hottest water you can theoretically get from it is 113F best case scenario?

How is that practical!?

What temperature do they want the DHW? If they want plumbing code specified 120F, set the DHW setting at 120F and eliminate the mix valve.

The new ASSE 1084 was developed as manufacturers claim their heaters or tankless, combos, etc can regulate as accurately as a mixing valve. I believe that is possible, and if the heater is listed to the standard then a mix valve is a moot point.

I'll check at AHR this years to see how many manufacturers are listing to that 1084, they asked for it and developed the standard

Seems odd Weil would pick an arbitrary number like 131F? With all the Legionella hysteria you think they would allow 140F operation.

Do they have it in ECO mode? That mode slows delivery and seems to cause issues with temperature stability, it did in my Lochinvar Combis.

ChrisJ

hot_rod said:

ChrisJ said:

hot_rod said:

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

It's max setting is 131F.
So if that's true, the hottest water you can theoretically get from it is 113F best case scenario?

How is that practical!?

What temperature do they want the DHW? If they want plumbing code specified 120F, set the DHW setting at 120F and eliminate the mix valve.

The new ASSE 1084 was developed as manufacturers claim their heaters or tankless, combos, etc can regulate as accurately as a mixing valve. I believe that is possible, and if the heater is listed to the standard then a mix valve is a moot point.

I'll check at AHR this years to see how many manufacturers are listing to that 1084, they asked for it and developed the standard

Seems odd Weil would pick an arbitrary number like 131F? With all the Legionella hysteria you think they would allow 140F operation.

Do they have it in ECO mode? That mode slows delivery and seems to cause issues with temperature stability, it did in my Lochinvar Combis.

They would like 120+ if it'll do it, 130 is even fine.
I agree the 131 is an odd number but I'm sure there's a reason somewhere. 55C?

I had asked about the Eco Vs Comfort mode last night but never got an answer back. I'll ask again.

ChrisJ

ChrisJ said:

hot_rod said:

ChrisJ said:

hot_rod said:

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

It's max setting is 131F.
So if that's true, the hottest water you can theoretically get from it is 113F best case scenario?

How is that practical!?

What temperature do they want the DHW? If they want plumbing code specified 120F, set the DHW setting at 120F and eliminate the mix valve.

The new ASSE 1084 was developed as manufacturers claim their heaters or tankless, combos, etc can regulate as accurately as a mixing valve. I believe that is possible, and if the heater is listed to the standard then a mix valve is a moot point.

I'll check at AHR this years to see how many manufacturers are listing to that 1084, they asked for it and developed the standard

Seems odd Weil would pick an arbitrary number like 131F? With all the Legionella hysteria you think they would allow 140F operation.

Do they have it in ECO mode? That mode slows delivery and seems to cause issues with temperature stability, it did in my Lochinvar Combis.

They would like 120+ if it'll do it, 130 is even fine.
I agree the 131 is an odd number but I'm sure there's a reason somewhere. 55C?

I had asked about the Eco Vs Comfort mode last night but never got an answer back. I'll ask again.

So I've been informed that since they maxed the mixing valve out, the problem is pretty much gone.

And it's in comfort mode.


Shame to hear their boiler is grossly oversized tho. There's no fixing that. I bet that house would do fine with 40-50K.

hot_rod

ChrisJ said:

ChrisJ said:

hot_rod said:

ChrisJ said:

hot_rod said:

A thermostatic mix valve needs at least 18° hotter supply than the mixed outlet to regulate accurately. Some brands ask for 22- 27°.

If the DHW is at 130 and the mix valve at 120, you do not have enough temperature delta for the mix valve to regulate accurately. So the mixed outlet will vary as the valve hunts for the set temperature.

Try increasing the DHW temperature, it should be able to reach 140F?

Or reduce the outlet from the mixer to 105F so you get more delta.

Also the mix valve should be at least 12" from the combis hot outlet to regulate best.

It's max setting is 131F.
So if that's true, the hottest water you can theoretically get from it is 113F best case scenario?

How is that practical!?

What temperature do they want the DHW? If they want plumbing code specified 120F, set the DHW setting at 120F and eliminate the mix valve.

The new ASSE 1084 was developed as manufacturers claim their heaters or tankless, combos, etc can regulate as accurately as a mixing valve. I believe that is possible, and if the heater is listed to the standard then a mix valve is a moot point.

I'll check at AHR this years to see how many manufacturers are listing to that 1084, they asked for it and developed the standard

Seems odd Weil would pick an arbitrary number like 131F? With all the Legionella hysteria you think they would allow 140F operation.

Do they have it in ECO mode? That mode slows delivery and seems to cause issues with temperature stability, it did in my Lochinvar Combis.

They would like 120+ if it'll do it, 130 is even fine.
I agree the 131 is an odd number but I'm sure there's a reason somewhere. 55C?

I had asked about the Eco Vs Comfort mode last night but never got an answer back. I'll ask again.

So I've been informed that since they maxed the mixing valve out, the problem is pretty much gone.

And it's in comfort mode.


Shame to hear their boiler is grossly oversized tho. There's no fixing that. I bet that house would do fine with 40-50K.

The boiler has a 15,000 BTU/hr minimum modulation. Does the control allow you to lock in a firing rate?
Some of the fire tube models allow you to lock them down, some allow ramp delay, one or both of those functions would help match the boiler to the heat load better.

Certainly the ODR function should be used and dialed in.

drivenserb

> @hot_rod said:
> It always comes down to how much is enough, DHW. I suppose somewhat it depends on who is paying the DHW bill.
>
> I've been on both sides, my opinion is the rental building owner gets to decide how much DHW is available. I've lived with 30 gallon electric tanks in a rental apt with 6 ski bums one winter, we made it work.
>
> Pretty much the rest of the world survives on tankless or combis, very rare to find a tank type DHW source in Europe, maybe some hotels.
>
> If you have 2.5 gpm of continuous DHW available you adjust to that supply. If you give them 80 gallons of tank supplied DHW, guess what

Yeah I understand what you mean however this is my primary residence. It’s not only going to effect the tennant it will effect my family Aswell.

drivenserb

I’ve narrowed it down and think I’m ready to settle on the following


High Efficiency Boiler
- Navien 150,000 BTU Model 150NHB

Indirect Storage Tank
- 50 Gallon Stainless Steel Trin & Stor

flat_twin

How big is your current power vented water heater? Does it keep up with DHW needs? FWIW, our 40 gallon indirect recovers in 10-12 minutes. We've had as many as five back to back showers and never run out of hot water. Indirect is set at 140 degrees, mixed down to 125. Boiler supply is set at 160 degrees for DHW.

The indirect allows you to use a right sized boiler for heating your home and rental so why go with a 150k btu boiler when you only need 80k?

psb75

This last question about a "right sized boiler" is a good one. You should consider it.

drivenserb

> @flat_twin said:
> How big is your current power vented water heater? Does it keep up with DHW needs? FWIW, our 40 gallon indirect recovers in 10-12 minutes. We've had as many as five back to back showers and never run out of hot water. Indirect is set at 140 degrees, mixed down to 125. Boiler supply is set at 160 degrees for DHW.
>
> The indirect allows you to use a right sized boiler for heating your home and rental so why go with a 150k btu boiler when you only need 80k?

My power vented is around 40 gallon not 100% sure but we run out of hot water in less than 2 showers. Yes I know there is a quick recovery with the indirect but I don’t want to chance loosing hot water. He quoted me a 110K btu unit but I asked for something bigger. Would it be an issue if I get a larger boiler or am I just loosing some efficiency. I’ve been told I need 100k BTU to heat my home. My current boiler is 150k BTU.

My house is a double brick 2 story home with zero insulation in the walls when it’s really cold I’m worried I won’t have enough power to heat the home. With the 110k btu unit.

flat_twin

First of all, does your current boiler keep the house warm all winter? You could do your own heat loss calculation with the Slant Fin app if you want some assurance that 100K btu is enough to heat your home on the coldest day. That app seems to have a 20% fudge factor built in. I found that to be true when I used it and compared against a fuel useage based heat loss. A more thorough assessment of your current heating system like exactly what boiler your have now, how many zones, the type of emitters, finned baseboard , cast iron radiators etc would help determine if you'll be able to take full advantage of a modcon boiler. At best, a right sized boiler will run very long cycles providing just enough btus to cover heat loss no matter the outdoor temperature. At worst, an oversized boiler will short cycle, starting and stopping frequently resulting in poor efficiency and excess wear and tear.

Likewise, a comparison of your current DHW system to the options you were given means you need to know specifics of your current system and how it is performing. You say you run out of hot water in two showers or less. That's very significant. Your current water heater either has problems, has always been a poor performer per lousy setup or was never a good match for your hot water needs. What is the btu output of your current water heater. Verify the temperature setting. Is it mixed down before going to the faucets? GPM rating of your shower heads was already mentioned as was big demands like a large tub, multiple showers going at one time. I think Zman's suggestion of a 60-80 gallon indirect is a good one per the details of the rental shower you say you'll be keeping plus whatever DHW needs your own residence may have at the same time.

motoguy128

Downside to a combi is whenever there is a call for DHW, you lose space heat for whatever delay is set. Default is 5 minutes I think. I set them to 1 minute. But the internal 3 way valve has to shift since there is no storage. So in the evening with cooking dishes, bathroom use, showers you will not have heat for all of those use periods plus the delay.

With in slab radiant floor heat or cast iron radiators , that’s not a big deal, it can catch up. But with Low mass fin tube or medium mass like under floor radiant or panel radiators it could be a problem.

But a combi is significantly cheaper in equipment cost and installation. But IMO don’t belong in some Heating applications.

On top of that, the flow rate on the internal pump is fixed.

On the Navien, min fire is almost the same on the 240 compared to the 210 or even 180 model so might as well go for the 240 for more DHW capacity.

motoguy128

On the flip side a 40 gallon indirect with a 80k output boiler will give you 2 gpm continuous evening with 77f temp rise mid winter. A single shower uses less than that.

One more side note, modern washer softer use on/off tempering (Pulse width modulation) of hot water not a modulating mixing valve so you get short bursts of hot water on any warm water setting. Not Efficient or ideal with a Tankless or combi.

tim smith

My .02 worth. 1st, verify heat loss, size boiler within 20% of heat loss. 2nd, based on the rain shower and largish tub I would probably go with 80 gallon indirect if I wanted to be pretty safe on sizing. My go to is lochinvar KHB/WHB model boiler with their SIT080 indirect. Sounds like it would either be a 110 or 155 size boiler. The KHB is floor model , WHB is wall mount.
Good luck

hot_rod

The boiler needs to size to the largest load.

In todays well insulated homes, the DHW load can far exceed the heating load. A 50K input boiler is probably on the small side of realistic DHW source.

Or a very large indirect to supply DHW as a dump load function and allow the small 35K boiler an hour or more to recover.

A BTU is a BTU and it takes a lot of them if you want fast heat transfer.

Henry

You are in Toronto and I in Montreal. While TO does not get as cold as Montreal, , you should be able to do a heat loss calculation using some of the programs available. The gas utility here uses 3.5 BTU per cubic feet of liveable space not including the basement. So that is a start for the heating load. A minimum of 10% extra for your area for domestic hot water indirect. Go with Lochinvar or HTP for boiler and indirect. Parts are easily available in TO and same here. BTW in Canada the minimum hot water temperature of the tank is 140F but the new plumbing codes requires max 120F at the faucet. You should put a tempering valve on the outlet of the tank.